diff options
Diffstat (limited to 'Documentation/i2c')
23 files changed, 2422 insertions, 678 deletions
diff --git a/Documentation/i2c/busses/i2c-i801.rst b/Documentation/i2c/busses/i2c-i801.rst index b83da0e94184..10eced6c2e46 100644 --- a/Documentation/i2c/busses/i2c-i801.rst +++ b/Documentation/i2c/busses/i2c-i801.rst @@ -43,6 +43,11 @@ Supported adapters: * Intel Elkhart Lake (PCH) * Intel Tiger Lake (PCH) * Intel Jasper Lake (SOC) + * Intel Emmitsburg (PCH) + * Intel Alder Lake (PCH) + * Intel Raptor Lake (PCH) + * Intel Meteor Lake (SOC and PCH) + * Intel Birch Stream (SOC) Datasheets: Publicly available at the Intel website diff --git a/Documentation/i2c/busses/i2c-parport-light.rst b/Documentation/i2c/busses/i2c-parport-light.rst deleted file mode 100644 index e73af975d2c8..000000000000 --- a/Documentation/i2c/busses/i2c-parport-light.rst +++ /dev/null @@ -1,24 +0,0 @@ -=============================== -Kernel driver i2c-parport-light -=============================== - -Author: Jean Delvare <jdelvare@suse.de> - -This driver is a light version of i2c-parport. It doesn't depend -on the parport driver, and uses direct I/O access instead. This might be -preferred on embedded systems where wasting memory for the clean but heavy -parport handling is not an option. The drawback is a reduced portability -and the impossibility to daisy-chain other parallel port devices. - -Please see i2c-parport for documentation. - -Module parameters: - -* type: type of adapter (see i2c-parport or modinfo) - -* base: base I/O address - Default is 0x378 which is fairly common for parallel ports, at least on PC. - -* irq: optional IRQ - This must be passed if you want SMBus alert support, assuming your adapter - actually supports this. diff --git a/Documentation/i2c/busses/i2c-piix4.rst b/Documentation/i2c/busses/i2c-piix4.rst index cc9000259223..07fe6f6f4b18 100644 --- a/Documentation/i2c/busses/i2c-piix4.rst +++ b/Documentation/i2c/busses/i2c-piix4.rst @@ -64,7 +64,7 @@ correct address for this module, you could get in big trouble (read: crashes, data corruption, etc.). Try this only as a last resort (try BIOS updates first, for example), and backup first! An even more dangerous option is 'force_addr=<IOPORT>'. This will not only enable the PIIX4 like -'force' foes, but it will also set a new base I/O port address. The SMBus +'force' does, but it will also set a new base I/O port address. The SMBus parts of the PIIX4 needs a range of 8 of these addresses to function correctly. If these addresses are already reserved by some other device, you will get into big trouble! DON'T USE THIS IF YOU ARE NOT VERY SURE @@ -86,15 +86,15 @@ If you own Force CPCI735 motherboard or other OSB4 based systems you may need to change the SMBus Interrupt Select register so the SMBus controller uses the SMI mode. -1) Use lspci command and locate the PCI device with the SMBus controller: +1) Use ``lspci`` command and locate the PCI device with the SMBus controller: 00:0f.0 ISA bridge: ServerWorks OSB4 South Bridge (rev 4f) The line may vary for different chipsets. Please consult the driver source - for all possible PCI ids (and lspci -n to match them). Lets assume the + for all possible PCI ids (and ``lspci -n`` to match them). Let's assume the device is located at 00:0f.0. 2) Now you just need to change the value in 0xD2 register. Get it first with - command: lspci -xxx -s 00:0f.0 + command: ``lspci -xxx -s 00:0f.0`` If the value is 0x3 then you need to change it to 0x1: - setpci -s 00:0f.0 d2.b=1 + ``setpci -s 00:0f.0 d2.b=1`` Please note that you don't need to do that in all cases, just when the SMBus is not working properly. @@ -109,6 +109,3 @@ which can easily get corrupted due to a state machine bug. These are mostly Thinkpad laptops, but desktop systems may also be affected. We have no list of all affected systems, so the only safe solution was to prevent access to the SMBus on all IBM systems (detected using DMI data.) - -For additional information, read: -http://www.lm-sensors.org/browser/lm-sensors/trunk/README diff --git a/Documentation/i2c/busses/index.rst b/Documentation/i2c/busses/index.rst index 2a26e251a335..5e4077b08d86 100644 --- a/Documentation/i2c/busses/index.rst +++ b/Documentation/i2c/busses/index.rst @@ -20,7 +20,6 @@ I2C Bus Drivers i2c-nforce2 i2c-nvidia-gpu i2c-ocores - i2c-parport-light i2c-parport i2c-pca-isa i2c-piix4 diff --git a/Documentation/i2c/dev-interface.rst b/Documentation/i2c/dev-interface.rst index 69c23a3c2b1b..c277a8e1202b 100644 --- a/Documentation/i2c/dev-interface.rst +++ b/Documentation/i2c/dev-interface.rst @@ -1,27 +1,27 @@ -==================== -I2C Device Interface -==================== +============================================ +Implementing I2C device drivers in userspace +============================================ -Usually, i2c devices are controlled by a kernel driver. But it is also +Usually, I2C devices are controlled by a kernel driver. But it is also possible to access all devices on an adapter from userspace, through the /dev interface. You need to load module i2c-dev for this. -Each registered i2c adapter gets a number, counting from 0. You can +Each registered I2C adapter gets a number, counting from 0. You can examine /sys/class/i2c-dev/ to see what number corresponds to which adapter. Alternatively, you can run "i2cdetect -l" to obtain a formatted list of all -i2c adapters present on your system at a given time. i2cdetect is part of +I2C adapters present on your system at a given time. i2cdetect is part of the i2c-tools package. I2C device files are character device files with major device number 89 and a minor device number corresponding to the number assigned as explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ..., -i2c-10, ...). All 256 minor device numbers are reserved for i2c. +i2c-10, ...). All 256 minor device numbers are reserved for I2C. C example ========= -So let's say you want to access an i2c adapter from a C program. +So let's say you want to access an I2C adapter from a C program. First, you need to include these two headers:: #include <linux/i2c-dev.h> @@ -66,7 +66,7 @@ the device supports them. Both are illustrated below:: /* Using SMBus commands */ res = i2c_smbus_read_word_data(file, reg); if (res < 0) { - /* ERROR HANDLING: i2c transaction failed */ + /* ERROR HANDLING: I2C transaction failed */ } else { /* res contains the read word */ } @@ -79,12 +79,12 @@ the device supports them. Both are illustrated below:: buf[1] = 0x43; buf[2] = 0x65; if (write(file, buf, 3) != 3) { - /* ERROR HANDLING: i2c transaction failed */ + /* ERROR HANDLING: I2C transaction failed */ } /* Using I2C Read, equivalent of i2c_smbus_read_byte(file) */ if (read(file, buf, 1) != 1) { - /* ERROR HANDLING: i2c transaction failed */ + /* ERROR HANDLING: I2C transaction failed */ } else { /* buf[0] contains the read byte */ } @@ -144,11 +144,11 @@ The following IOCTLs are defined: If possible, use the provided ``i2c_smbus_*`` methods described below instead of issuing direct ioctls. -You can do plain i2c transactions by using read(2) and write(2) calls. +You can do plain I2C transactions by using read(2) and write(2) calls. You do not need to pass the address byte; instead, set it through ioctl I2C_SLAVE before you try to access the device. -You can do SMBus level transactions (see documentation file smbus-protocol +You can do SMBus level transactions (see documentation file smbus-protocol.rst for details) through the following functions:: __s32 i2c_smbus_write_quick(int file, __u8 value); @@ -159,6 +159,8 @@ for details) through the following functions:: __s32 i2c_smbus_read_word_data(int file, __u8 command); __s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value); __s32 i2c_smbus_process_call(int file, __u8 command, __u16 value); + __s32 i2c_smbus_block_process_call(int file, __u8 command, __u8 length, + __u8 *values); __s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values); __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length, __u8 *values); diff --git a/Documentation/i2c/dma-considerations.rst b/Documentation/i2c/dma-considerations.rst index 203002054120..142d52ce9ebb 100644 --- a/Documentation/i2c/dma-considerations.rst +++ b/Documentation/i2c/dma-considerations.rst @@ -2,7 +2,7 @@ Linux I2C and DMA ================= -Given that i2c is a low-speed bus, over which the majority of messages +Given that I2C is a low-speed bus, over which the majority of messages transferred are small, it is not considered a prime user of DMA access. At this time of writing, only 10% of I2C bus master drivers have DMA support implemented. And the vast majority of transactions are so small that setting up diff --git a/Documentation/i2c/fault-codes.rst b/Documentation/i2c/fault-codes.rst index 80b14e718b52..b0864d1268bd 100644 --- a/Documentation/i2c/fault-codes.rst +++ b/Documentation/i2c/fault-codes.rst @@ -39,6 +39,10 @@ Also, codes returned by adapter probe methods follow rules which are specific to their host bus (such as PCI, or the platform bus). +EAFNOSUPPORT + Returned by I2C adapters not supporting 10 bit addresses when + they are requested to use such an address. + EAGAIN Returned by I2C adapters when they lose arbitration in master transmit mode: some other master was transmitting different diff --git a/Documentation/i2c/gpio-fault-injection.rst b/Documentation/i2c/gpio-fault-injection.rst index 9dca6ec7d266..91d23889abd5 100644 --- a/Documentation/i2c/gpio-fault-injection.rst +++ b/Documentation/i2c/gpio-fault-injection.rst @@ -93,7 +93,7 @@ bus arbitration against another master in a multi-master setup. ------------------ This file is write only and you need to write the duration of the arbitration -intereference (in µs, maximum is 100ms). The calling process will then sleep +interference (in µs, maximum is 100ms). The calling process will then sleep and wait for the next bus clock. The process is interruptible, though. Arbitration lost is achieved by waiting for SCL going down by the master under diff --git a/Documentation/i2c/i2c-address-translators.rst b/Documentation/i2c/i2c-address-translators.rst new file mode 100644 index 000000000000..6845c114e472 --- /dev/null +++ b/Documentation/i2c/i2c-address-translators.rst @@ -0,0 +1,96 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================= +I2C Address Translators +======================= + +Author: Luca Ceresoli <luca@lucaceresoli.net> +Author: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> + +Description +----------- + +An I2C Address Translator (ATR) is a device with an I2C slave parent +("upstream") port and N I2C master child ("downstream") ports, and +forwards transactions from upstream to the appropriate downstream port +with a modified slave address. The address used on the parent bus is +called the "alias" and is (potentially) different from the physical +slave address of the child bus. Address translation is done by the +hardware. + +An ATR looks similar to an i2c-mux except: + - the address on the parent and child busses can be different + - there is normally no need to select the child port; the alias used on the + parent bus implies it + +The ATR functionality can be provided by a chip with many other features. +The kernel i2c-atr provides a helper to implement an ATR within a driver. + +The ATR creates a new I2C "child" adapter on each child bus. Adding +devices on the child bus ends up in invoking the driver code to select +an available alias. Maintaining an appropriate pool of available aliases +and picking one for each new device is up to the driver implementer. The +ATR maintains a table of currently assigned alias and uses it to modify +all I2C transactions directed to devices on the child buses. + +A typical example follows. + +Topology:: + + Slave X @ 0x10 + .-----. | + .-----. | |---+---- B + | CPU |--A--| ATR | + `-----' | |---+---- C + `-----' | + Slave Y @ 0x10 + +Alias table: + +A, B and C are three physical I2C busses, electrically independent from +each other. The ATR receives the transactions initiated on bus A and +propagates them on bus B or bus C or none depending on the device address +in the transaction and based on the alias table. + +Alias table: + +.. table:: + + =============== ===== + Client Alias + =============== ===== + X (bus B, 0x10) 0x20 + Y (bus C, 0x10) 0x30 + =============== ===== + +Transaction: + + - Slave X driver requests a transaction (on adapter B), slave address 0x10 + - ATR driver finds slave X is on bus B and has alias 0x20, rewrites + messages with address 0x20, forwards to adapter A + - Physical I2C transaction on bus A, slave address 0x20 + - ATR chip detects transaction on address 0x20, finds it in table, + propagates transaction on bus B with address translated to 0x10, + keeps clock stretched on bus A waiting for reply + - Slave X chip (on bus B) detects transaction at its own physical + address 0x10 and replies normally + - ATR chip stops clock stretching and forwards reply on bus A, + with address translated back to 0x20 + - ATR driver receives the reply, rewrites messages with address 0x10 + as they were initially + - Slave X driver gets back the msgs[], with reply and address 0x10 + +Usage: + + 1. In the driver (typically in the probe function) add an ATR by + calling i2c_atr_new() passing attach/detach callbacks + 2. When the attach callback is called pick an appropriate alias, + configure it in the chip and return the chosen alias in the + alias_id parameter + 3. When the detach callback is called, deconfigure the alias from + the chip and put the alias back in the pool for later usage + +I2C ATR functions and data structures +------------------------------------- + +.. kernel-doc:: include/linux/i2c-atr.h diff --git a/Documentation/i2c/i2c-protocol.rst b/Documentation/i2c/i2c-protocol.rst index 2f8fcf671b2e..df0febfe6410 100644 --- a/Documentation/i2c/i2c-protocol.rst +++ b/Documentation/i2c/i2c-protocol.rst @@ -1,26 +1,23 @@ -============ -I2C Protocol -============ +================ +The I2C Protocol +================ -This document describes the i2c protocol. Or will, when it is finished :-) +This document is an overview of the basic I2C transactions and the kernel +APIs to perform them. Key to symbols ============== =============== ============================================================= -S (1 bit) : Start bit -P (1 bit) : Stop bit -Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0. -A, NA (1 bit) : Accept and reverse accept bit. -Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to +S Start condition +P Stop condition +Rd/Wr (1 bit) Read/Write bit. Rd equals 1, Wr equals 0. +A, NA (1 bit) Acknowledge (ACK) and Not Acknowledge (NACK) bit +Addr (7 bits) I2C 7 bit address. Note that this can be expanded to get a 10 bit I2C address. -Comm (8 bits): Command byte, a data byte which often selects a register on - the device. -Data (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh - for 16 bit data. -Count (8 bits): A data byte containing the length of a block operation. +Data (8 bits) A plain data byte. -[..]: Data sent by I2C device, as opposed to data sent by the +[..] Data sent by I2C device, as opposed to data sent by the host adapter. =============== ============================================================= @@ -28,7 +25,7 @@ Count (8 bits): A data byte containing the length of a block operation. Simple send transaction ======================= -This corresponds to i2c_master_send:: +Implemented by i2c_master_send():: S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P @@ -36,7 +33,7 @@ This corresponds to i2c_master_send:: Simple receive transaction ========================== -This corresponds to i2c_master_recv:: +Implemented by i2c_master_recv():: S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P @@ -44,11 +41,11 @@ This corresponds to i2c_master_recv:: Combined transactions ===================== -This corresponds to i2c_transfer +Implemented by i2c_transfer(). -They are just like the above transactions, but instead of a stop bit P -a start bit S is sent and the transaction continues. An example of -a byte read, followed by a byte write:: +They are just like the above transactions, but instead of a stop +condition P a start condition S is sent and the transaction continues. +An example of a byte read, followed by a byte write:: S Addr Rd [A] [Data] NA S Addr Wr [A] Data [A] P @@ -57,7 +54,7 @@ Modified transactions ===================== The following modifications to the I2C protocol can also be generated by -setting these flags for i2c messages. With the exception of I2C_M_NOSTART, they +setting these flags for I2C messages. With the exception of I2C_M_NOSTART, they are usually only needed to work around device issues: I2C_M_IGNORE_NAK: @@ -77,8 +74,9 @@ I2C_M_NOSTART: S Addr Rd [A] [Data] NA Data [A] P If you set the I2C_M_NOSTART variable for the first partial message, - we do not generate Addr, but we do generate the startbit S. This will - probably confuse all other clients on your bus, so don't try this. + we do not generate Addr, but we do generate the start condition S. + This will probably confuse all other clients on your bus, so don't + try this. This is often used to gather transmits from multiple data buffers in system memory into something that appears as a single transfer to the diff --git a/Documentation/i2c/i2c-sysfs.rst b/Documentation/i2c/i2c-sysfs.rst new file mode 100644 index 000000000000..78c54c658fa1 --- /dev/null +++ b/Documentation/i2c/i2c-sysfs.rst @@ -0,0 +1,387 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============== +Linux I2C Sysfs +=============== + +Overview +======== + +I2C topology can be complex because of the existence of I2C MUX +(I2C Multiplexer). The Linux +kernel abstracts the MUX channels into logical I2C bus numbers. However, there +is a gap of knowledge to map from the I2C bus physical number and MUX topology +to logical I2C bus number. This doc is aimed to fill in this gap, so the +audience (hardware engineers and new software developers for example) can learn +the concept of logical I2C buses in the kernel, by knowing the physical I2C +topology and navigating through the I2C sysfs in Linux shell. This knowledge is +useful and essential to use ``i2c-tools`` for the purpose of development and +debugging. + +Target audience +--------------- + +People who need to use Linux shell to interact with I2C subsystem on a system +which the Linux is running on. + +Prerequisites +------------- + +1. Knowledge of general Linux shell file system commands and operations. + +2. General knowledge of I2C, I2C MUX and I2C topology. + +Location of I2C Sysfs +===================== + +Typically, the Linux Sysfs filesystem is mounted at the ``/sys`` directory, +so you can find the I2C Sysfs under ``/sys/bus/i2c/devices`` +where you can directly ``cd`` to it. +There is a list of symbolic links under that directory. The links that +start with ``i2c-`` are I2C buses, which may be either physical or logical. The +other links that begin with numbers and end with numbers are I2C devices, where +the first number is I2C bus number, and the second number is I2C address. + +Google Pixel 3 phone for example:: + + blueline:/sys/bus/i2c/devices $ ls + 0-0008 0-0061 1-0028 3-0043 4-0036 4-0041 i2c-1 i2c-3 + 0-000c 0-0066 2-0049 4-000b 4-0040 i2c-0 i2c-2 i2c-4 + +``i2c-2`` is an I2C bus whose number is 2, and ``2-0049`` is an I2C device +on bus 2 address 0x49 bound with a kernel driver. + +Terminology +=========== + +First, let us define some terms to avoid confusion in later sections. + +(Physical) I2C Bus Controller +----------------------------- + +The hardware system that the Linux kernel is running on may have multiple +physical I2C bus controllers. The controllers are hardware and physical, and the +system may define multiple registers in the memory space to manipulate the +controllers. Linux kernel has I2C bus drivers under source directory +``drivers/i2c/busses`` to translate kernel I2C API into register +operations for different systems. This terminology is not limited to Linux +kernel only. + +I2C Bus Physical Number +----------------------- + +For each physical I2C bus controller, the system vendor may assign a physical +number to each controller. For example, the first I2C bus controller which has +the lowest register addresses may be called ``I2C-0``. + +Logical I2C Bus +--------------- + +Every I2C bus number you see in Linux I2C Sysfs is a logical I2C bus with a +number assigned. This is similar to the fact that software code is usually +written upon virtual memory space, instead of physical memory space. + +Each logical I2C bus may be an abstraction of a physical I2C bus controller, or +an abstraction of a channel behind an I2C MUX. In case it is an abstraction of a +MUX channel, whenever we access an I2C device via a such logical bus, the kernel +will switch the I2C MUX for you to the proper channel as part of the +abstraction. + +Physical I2C Bus +---------------- + +If the logical I2C bus is a direct abstraction of a physical I2C bus controller, +let us call it a physical I2C bus. + +Caveat +------ + +This may be a confusing part for people who only know about the physical I2C +design of a board. It is actually possible to rename the I2C bus physical number +to a different number in logical I2C bus level in Device Tree Source (DTS) under +section ``aliases``. See ``arch/arm/boot/dts/nuvoton-npcm730-gsj.dts`` +for an example of DTS file. + +Best Practice: **(To kernel software developers)** It is better to keep the I2C +bus physical number the same as their corresponding logical I2C bus number, +instead of renaming or mapping them, so that it may be less confusing to other +users. These physical I2C buses can be served as good starting points for I2C +MUX fanouts. For the following examples, we will assume that the physical I2C +bus has a number same as their I2C bus physical number. + +Walk through Logical I2C Bus +============================ + +For the following content, we will use a more complex I2C topology as an +example. Here is a brief graph for the I2C topology. If you do not understand +this graph at first glance, do not be afraid to continue reading this doc +and review it when you finish reading. + +:: + + i2c-7 (physical I2C bus controller 7) + `-- 7-0071 (4-channel I2C MUX at 0x71) + |-- i2c-60 (channel-0) + |-- i2c-73 (channel-1) + | |-- 73-0040 (I2C sensor device with hwmon directory) + | |-- 73-0070 (I2C MUX at 0x70, exists in DTS, but failed to probe) + | `-- 73-0072 (8-channel I2C MUX at 0x72) + | |-- i2c-78 (channel-0) + | |-- ... (channel-1...6, i2c-79...i2c-84) + | `-- i2c-85 (channel-7) + |-- i2c-86 (channel-2) + `-- i2c-203 (channel-3) + +Distinguish Physical and Logical I2C Bus +---------------------------------------- + +One simple way to distinguish between a physical I2C bus and a logical I2C bus, +is to read the symbolic link ``device`` under the I2C bus directory by using +command ``ls -l`` or ``readlink``. + +An alternative symbolic link to check is ``mux_device``. This link only exists +in logical I2C bus directory which is fanned out from another I2C bus. +Reading this link will also tell you which I2C MUX device created +this logical I2C bus. + +If the symbolic link points to a directory ending with ``.i2c``, it should be a +physical I2C bus, directly abstracting a physical I2C bus controller. For +example:: + + $ readlink /sys/bus/i2c/devices/i2c-7/device + ../../f0087000.i2c + $ ls /sys/bus/i2c/devices/i2c-7/mux_device + ls: /sys/bus/i2c/devices/i2c-7/mux_device: No such file or directory + +In this case, ``i2c-7`` is a physical I2C bus, so it does not have the symbolic +link ``mux_device`` under its directory. And if the kernel software developer +follows the common practice by not renaming physical I2C buses, this should also +mean the physical I2C bus controller 7 of the system. + +On the other hand, if the symbolic link points to another I2C bus, the I2C bus +presented by the current directory has to be a logical bus. The I2C bus pointed +by the link is the parent bus which may be either a physical I2C bus or a +logical one. In this case, the I2C bus presented by the current directory +abstracts an I2C MUX channel under the parent bus. + +For example:: + + $ readlink /sys/bus/i2c/devices/i2c-73/device + ../../i2c-7 + $ readlink /sys/bus/i2c/devices/i2c-73/mux_device + ../7-0071 + +``i2c-73`` is a logical bus fanout by an I2C MUX under ``i2c-7`` +whose I2C address is 0x71. +Whenever we access an I2C device with bus 73, the kernel will always +switch the I2C MUX addressed 0x71 to the proper channel for you as part of the +abstraction. + +Finding out Logical I2C Bus Number +---------------------------------- + +In this section, we will describe how to find out the logical I2C bus number +representing certain I2C MUX channels based on the knowledge of physical +hardware I2C topology. + +In this example, we have a system which has a physical I2C bus 7 and not renamed +in DTS. There is a 4-channel MUX at address 0x71 on that bus. There is another +8-channel MUX at address 0x72 behind the channel 1 of the 0x71 MUX. Let us +navigate through Sysfs and find out the logical I2C bus number of the channel 3 +of the 0x72 MUX. + +First of all, let us go to the directory of ``i2c-7``:: + + ~$ cd /sys/bus/i2c/devices/i2c-7 + /sys/bus/i2c/devices/i2c-7$ ls + 7-0071 i2c-60 name subsystem + delete_device i2c-73 new_device uevent + device i2c-86 of_node + i2c-203 i2c-dev power + +There, we see the 0x71 MUX as ``7-0071``. Go inside it:: + + /sys/bus/i2c/devices/i2c-7$ cd 7-0071/ + /sys/bus/i2c/devices/i2c-7/7-0071$ ls -l + channel-0 channel-3 modalias power + channel-1 driver name subsystem + channel-2 idle_state of_node uevent + +Read the link ``channel-1`` using ``readlink`` or ``ls -l``:: + + /sys/bus/i2c/devices/i2c-7/7-0071$ readlink channel-1 + ../i2c-73 + +We find out that the channel 1 of 0x71 MUX on ``i2c-7`` is assigned +with a logical I2C bus number of 73. +Let us continue the journey to directory ``i2c-73`` in either ways:: + + # cd to i2c-73 under I2C Sysfs root + /sys/bus/i2c/devices/i2c-7/7-0071$ cd /sys/bus/i2c/devices/i2c-73 + /sys/bus/i2c/devices/i2c-73$ + + # cd the channel symbolic link + /sys/bus/i2c/devices/i2c-7/7-0071$ cd channel-1 + /sys/bus/i2c/devices/i2c-7/7-0071/channel-1$ + + # cd the link content + /sys/bus/i2c/devices/i2c-7/7-0071$ cd ../i2c-73 + /sys/bus/i2c/devices/i2c-7/i2c-73$ + +Either ways, you will end up in the directory of ``i2c-73``. Similar to above, +we can now find the 0x72 MUX and what logical I2C bus numbers +that its channels are assigned:: + + /sys/bus/i2c/devices/i2c-73$ ls + 73-0040 device i2c-83 new_device + 73-004e i2c-78 i2c-84 of_node + 73-0050 i2c-79 i2c-85 power + 73-0070 i2c-80 i2c-dev subsystem + 73-0072 i2c-81 mux_device uevent + delete_device i2c-82 name + /sys/bus/i2c/devices/i2c-73$ cd 73-0072 + /sys/bus/i2c/devices/i2c-73/73-0072$ ls + channel-0 channel-4 driver of_node + channel-1 channel-5 idle_state power + channel-2 channel-6 modalias subsystem + channel-3 channel-7 name uevent + /sys/bus/i2c/devices/i2c-73/73-0072$ readlink channel-3 + ../i2c-81 + +There, we find out the logical I2C bus number of the channel 3 of the 0x72 MUX +is 81. We can later use this number to switch to its own I2C Sysfs directory or +issue ``i2c-tools`` commands. + +Tip: Once you understand the I2C topology with MUX, command +`i2cdetect -l +<https://manpages.debian.org/unstable/i2c-tools/i2cdetect.8.en.html>`_ +in +`I2C Tools +<https://i2c.wiki.kernel.org/index.php/I2C_Tools>`_ +can give you +an overview of the I2C topology easily, if it is available on your system. For +example:: + + $ i2cdetect -l | grep -e '\-73' -e _7 | sort -V + i2c-7 i2c npcm_i2c_7 I2C adapter + i2c-73 i2c i2c-7-mux (chan_id 1) I2C adapter + i2c-78 i2c i2c-73-mux (chan_id 0) I2C adapter + i2c-79 i2c i2c-73-mux (chan_id 1) I2C adapter + i2c-80 i2c i2c-73-mux (chan_id 2) I2C adapter + i2c-81 i2c i2c-73-mux (chan_id 3) I2C adapter + i2c-82 i2c i2c-73-mux (chan_id 4) I2C adapter + i2c-83 i2c i2c-73-mux (chan_id 5) I2C adapter + i2c-84 i2c i2c-73-mux (chan_id 6) I2C adapter + i2c-85 i2c i2c-73-mux (chan_id 7) I2C adapter + +Pinned Logical I2C Bus Number +----------------------------- + +If not specified in DTS, when an I2C MUX driver is applied and the MUX device is +successfully probed, the kernel will assign the MUX channels with a logical bus +number based on the current biggest logical bus number incrementally. For +example, if the system has ``i2c-15`` as the highest logical bus number, and a +4-channel MUX is applied successfully, we will have ``i2c-16`` for the +MUX channel 0, and all the way to ``i2c-19`` for the MUX channel 3. + +The kernel software developer is able to pin the fanout MUX channels to a static +logical I2C bus number in the DTS. This doc will not go through the details on +how to implement this in DTS, but we can see an example in: +``arch/arm/boot/dts/aspeed-bmc-facebook-wedge400.dts`` + +In the above example, there is an 8-channel I2C MUX at address 0x70 on physical +I2C bus 2. The channel 2 of the MUX is defined as ``imux18`` in DTS, +and pinned to logical I2C bus number 18 with the line of ``i2c18 = &imux18;`` +in section ``aliases``. + +Take it further, it is possible to design a logical I2C bus number schema that +can be easily remembered by humans or calculated arithmetically. For example, we +can pin the fanout channels of a MUX on bus 3 to start at 30. So 30 will be the +logical bus number of the channel 0 of the MUX on bus 3, and 37 will be the +logical bus number of the channel 7 of the MUX on bus 3. + +I2C Devices +=========== + +In previous sections, we mostly covered the I2C bus. In this section, let us see +what we can learn from the I2C device directory whose link name is in the format +of ``${bus}-${addr}``. The ``${bus}`` part in the name is a logical I2C bus +decimal number, while the ``${addr}`` part is a hex number of the I2C address +of each device. + +I2C Device Directory Content +---------------------------- + +Inside each I2C device directory, there is a file named ``name``. +This file tells what device name it was used for the kernel driver to +probe this device. Use command ``cat`` to read its content. For example:: + + /sys/bus/i2c/devices/i2c-73$ cat 73-0040/name + ina230 + /sys/bus/i2c/devices/i2c-73$ cat 73-0070/name + pca9546 + /sys/bus/i2c/devices/i2c-73$ cat 73-0072/name + pca9547 + +There is a symbolic link named ``driver`` to tell what Linux kernel driver was +used to probe this device:: + + /sys/bus/i2c/devices/i2c-73$ readlink -f 73-0040/driver + /sys/bus/i2c/drivers/ina2xx + /sys/bus/i2c/devices/i2c-73$ readlink -f 73-0072/driver + /sys/bus/i2c/drivers/pca954x + +But if the link ``driver`` does not exist at the first place, +it may mean that the kernel driver failed to probe this device due to +some errors. The error may be found in ``dmesg``:: + + /sys/bus/i2c/devices/i2c-73$ ls 73-0070/driver + ls: 73-0070/driver: No such file or directory + /sys/bus/i2c/devices/i2c-73$ dmesg | grep 73-0070 + pca954x 73-0070: probe failed + pca954x 73-0070: probe failed + +Depending on what the I2C device is and what kernel driver was used to probe the +device, we may have different content in the device directory. + +I2C MUX Device +-------------- + +While you may be already aware of this in previous sections, an I2C MUX device +will have symbolic link ``channel-*`` inside its device directory. +These symbolic links point to their logical I2C bus directories:: + + /sys/bus/i2c/devices/i2c-73$ ls -l 73-0072/channel-* + lrwxrwxrwx ... 73-0072/channel-0 -> ../i2c-78 + lrwxrwxrwx ... 73-0072/channel-1 -> ../i2c-79 + lrwxrwxrwx ... 73-0072/channel-2 -> ../i2c-80 + lrwxrwxrwx ... 73-0072/channel-3 -> ../i2c-81 + lrwxrwxrwx ... 73-0072/channel-4 -> ../i2c-82 + lrwxrwxrwx ... 73-0072/channel-5 -> ../i2c-83 + lrwxrwxrwx ... 73-0072/channel-6 -> ../i2c-84 + lrwxrwxrwx ... 73-0072/channel-7 -> ../i2c-85 + +I2C Sensor Device / Hwmon +------------------------- + +I2C sensor device is also common to see. If they are bound by a kernel hwmon +(Hardware Monitoring) driver successfully, you will see a ``hwmon`` directory +inside the I2C device directory. Keep digging into it, you will find the Hwmon +Sysfs for the I2C sensor device:: + + /sys/bus/i2c/devices/i2c-73/73-0040/hwmon/hwmon17$ ls + curr1_input in0_lcrit_alarm name subsystem + device in1_crit power uevent + in0_crit in1_crit_alarm power1_crit update_interval + in0_crit_alarm in1_input power1_crit_alarm + in0_input in1_lcrit power1_input + in0_lcrit in1_lcrit_alarm shunt_resistor + +For more info on the Hwmon Sysfs, refer to the doc: + +../hwmon/sysfs-interface.rst + +Instantiate I2C Devices in I2C Sysfs +------------------------------------ + +Refer to section "Method 4: Instantiate from user-space" of instantiating-devices.rst diff --git a/Documentation/i2c/i2c-topology.rst b/Documentation/i2c/i2c-topology.rst index 0c1ae95f6a97..48fce0f7491b 100644 --- a/Documentation/i2c/i2c-topology.rst +++ b/Documentation/i2c/i2c-topology.rst @@ -1,9 +1,11 @@ -============ -I2C topology -============ +================================ +I2C muxes and complex topologies +================================ -There are a couple of reasons for building more complex i2c topologies -than a straight-forward i2c bus with one adapter and one or more devices. +There are a couple of reasons for building more complex I2C topologies +than a straight-forward I2C bus with one adapter and one or more devices. + +Some example use cases are: 1. A mux may be needed on the bus to prevent address collisions. @@ -11,20 +13,20 @@ than a straight-forward i2c bus with one adapter and one or more devices. may be needed to determine if it is ok to access the bus. 3. A device (particularly RF tuners) may want to avoid the digital noise - from the i2c bus, at least most of the time, and sits behind a gate + from the I2C bus, at least most of the time, and sits behind a gate that has to be operated before the device can be accessed. -Etc -=== +Several types of hardware components such as I2C muxes, I2C gates and I2C +arbitrators allow to handle such needs. -These constructs are represented as i2c adapter trees by Linux, where +These components are represented as I2C adapter trees by Linux, where each adapter has a parent adapter (except the root adapter) and zero or more child adapters. The root adapter is the actual adapter that issues -i2c transfers, and all adapters with a parent are part of an "i2c-mux" +I2C transfers, and all adapters with a parent are part of an "i2c-mux" object (quoted, since it can also be an arbitrator or a gate). Depending of the particular mux driver, something happens when there is -an i2c transfer on one of its child adapters. The mux driver can +an I2C transfer on one of its child adapters. The mux driver can obviously operate a mux, but it can also do arbitration with an external bus master or open a gate. The mux driver has two operations for this, select and deselect. select is called before the transfer and (the @@ -34,47 +36,8 @@ optional) deselect is called after the transfer. Locking ======= -There are two variants of locking available to i2c muxes, they can be -mux-locked or parent-locked muxes. As is evident from below, it can be -useful to know if a mux is mux-locked or if it is parent-locked. The -following list was correct at the time of writing: - -In drivers/i2c/muxes/: - -====================== ============================================= -i2c-arb-gpio-challenge Parent-locked -i2c-mux-gpio Normally parent-locked, mux-locked iff - all involved gpio pins are controlled by the - same i2c root adapter that they mux. -i2c-mux-gpmux Normally parent-locked, mux-locked iff - specified in device-tree. -i2c-mux-ltc4306 Mux-locked -i2c-mux-mlxcpld Parent-locked -i2c-mux-pca9541 Parent-locked -i2c-mux-pca954x Parent-locked -i2c-mux-pinctrl Normally parent-locked, mux-locked iff - all involved pinctrl devices are controlled - by the same i2c root adapter that they mux. -i2c-mux-reg Parent-locked -====================== ============================================= - -In drivers/iio/: - -====================== ============================================= -gyro/mpu3050 Mux-locked -imu/inv_mpu6050/ Mux-locked -====================== ============================================= - -In drivers/media/: - -======================= ============================================= -dvb-frontends/lgdt3306a Mux-locked -dvb-frontends/m88ds3103 Parent-locked -dvb-frontends/rtl2830 Parent-locked -dvb-frontends/rtl2832 Mux-locked -dvb-frontends/si2168 Mux-locked -usb/cx231xx/ Parent-locked -======================= ============================================= +There are two variants of locking available to I2C muxes, they can be +mux-locked or parent-locked muxes. Mux-locked muxes @@ -83,46 +46,14 @@ Mux-locked muxes Mux-locked muxes does not lock the entire parent adapter during the full select-transfer-deselect transaction, only the muxes on the parent adapter are locked. Mux-locked muxes are mostly interesting if the -select and/or deselect operations must use i2c transfers to complete +select and/or deselect operations must use I2C transfers to complete their tasks. Since the parent adapter is not fully locked during the -full transaction, unrelated i2c transfers may interleave the different +full transaction, unrelated I2C transfers may interleave the different stages of the transaction. This has the benefit that the mux driver may be easier and cleaner to implement, but it has some caveats. -==== ===================================================================== -ML1. If you build a topology with a mux-locked mux being the parent - of a parent-locked mux, this might break the expectation from the - parent-locked mux that the root adapter is locked during the - transaction. - -ML2. It is not safe to build arbitrary topologies with two (or more) - mux-locked muxes that are not siblings, when there are address - collisions between the devices on the child adapters of these - non-sibling muxes. - - I.e. the select-transfer-deselect transaction targeting e.g. device - address 0x42 behind mux-one may be interleaved with a similar - operation targeting device address 0x42 behind mux-two. The - intension with such a topology would in this hypothetical example - be that mux-one and mux-two should not be selected simultaneously, - but mux-locked muxes do not guarantee that in all topologies. - -ML3. A mux-locked mux cannot be used by a driver for auto-closing - gates/muxes, i.e. something that closes automatically after a given - number (one, in most cases) of i2c transfers. Unrelated i2c transfers - may creep in and close prematurely. - -ML4. If any non-i2c operation in the mux driver changes the i2c mux state, - the driver has to lock the root adapter during that operation. - Otherwise garbage may appear on the bus as seen from devices - behind the mux, when an unrelated i2c transfer is in flight during - the non-i2c mux-changing operation. -==== ===================================================================== - - Mux-locked Example ------------------- - +~~~~~~~~~~~~~~~~~~ :: @@ -137,14 +68,14 @@ Mux-locked Example When there is an access to D1, this happens: - 1. Someone issues an i2c-transfer to D1. + 1. Someone issues an I2C transfer to D1. 2. M1 locks muxes on its parent (the root adapter in this case). 3. M1 calls ->select to ready the mux. - 4. M1 (presumably) does some i2c-transfers as part of its select. - These transfers are normal i2c-transfers that locks the parent + 4. M1 (presumably) does some I2C transfers as part of its select. + These transfers are normal I2C transfers that locks the parent adapter. - 5. M1 feeds the i2c-transfer from step 1 to its parent adapter as a - normal i2c-transfer that locks the parent adapter. + 5. M1 feeds the I2C transfer from step 1 to its parent adapter as a + normal I2C transfer that locks the parent adapter. 6. M1 calls ->deselect, if it has one. 7. Same rules as in step 4, but for ->deselect. 8. M1 unlocks muxes on its parent. @@ -153,36 +84,55 @@ This means that accesses to D2 are lockout out for the full duration of the entire operation. But accesses to D3 are possibly interleaved at any point. +Mux-locked caveats +~~~~~~~~~~~~~~~~~~ + +When using a mux-locked mux, be aware of the following restrictions: + +[ML1] + If you build a topology with a mux-locked mux being the parent + of a parent-locked mux, this might break the expectation from the + parent-locked mux that the root adapter is locked during the + transaction. + +[ML2] + It is not safe to build arbitrary topologies with two (or more) + mux-locked muxes that are not siblings, when there are address + collisions between the devices on the child adapters of these + non-sibling muxes. + + I.e. the select-transfer-deselect transaction targeting e.g. device + address 0x42 behind mux-one may be interleaved with a similar + operation targeting device address 0x42 behind mux-two. The + intent with such a topology would in this hypothetical example + be that mux-one and mux-two should not be selected simultaneously, + but mux-locked muxes do not guarantee that in all topologies. + +[ML3] + A mux-locked mux cannot be used by a driver for auto-closing + gates/muxes, i.e. something that closes automatically after a given + number (one, in most cases) of I2C transfers. Unrelated I2C transfers + may creep in and close prematurely. + +[ML4] + If any non-I2C operation in the mux driver changes the I2C mux state, + the driver has to lock the root adapter during that operation. + Otherwise garbage may appear on the bus as seen from devices + behind the mux, when an unrelated I2C transfer is in flight during + the non-I2C mux-changing operation. + Parent-locked muxes ------------------- Parent-locked muxes lock the parent adapter during the full select- transfer-deselect transaction. The implication is that the mux driver -has to ensure that any and all i2c transfers through that parent -adapter during the transaction are unlocked i2c transfers (using e.g. -__i2c_transfer), or a deadlock will follow. There are a couple of -caveats. - -==== ==================================================================== -PL1. If you build a topology with a parent-locked mux being the child - of another mux, this might break a possible assumption from the - child mux that the root adapter is unused between its select op - and the actual transfer (e.g. if the child mux is auto-closing - and the parent mux issus i2c-transfers as part of its select). - This is especially the case if the parent mux is mux-locked, but - it may also happen if the parent mux is parent-locked. - -PL2. If select/deselect calls out to other subsystems such as gpio, - pinctrl, regmap or iio, it is essential that any i2c transfers - caused by these subsystems are unlocked. This can be convoluted to - accomplish, maybe even impossible if an acceptably clean solution - is sought. -==== ==================================================================== - +has to ensure that any and all I2C transfers through that parent +adapter during the transaction are unlocked I2C transfers (using e.g. +__i2c_transfer), or a deadlock will follow. Parent-locked Example ---------------------- +~~~~~~~~~~~~~~~~~~~~~ :: @@ -197,25 +147,45 @@ Parent-locked Example When there is an access to D1, this happens: - 1. Someone issues an i2c-transfer to D1. + 1. Someone issues an I2C transfer to D1. 2. M1 locks muxes on its parent (the root adapter in this case). 3. M1 locks its parent adapter. 4. M1 calls ->select to ready the mux. - 5. If M1 does any i2c-transfers (on this root adapter) as part of - its select, those transfers must be unlocked i2c-transfers so + 5. If M1 does any I2C transfers (on this root adapter) as part of + its select, those transfers must be unlocked I2C transfers so that they do not deadlock the root adapter. - 6. M1 feeds the i2c-transfer from step 1 to the root adapter as an - unlocked i2c-transfer, so that it does not deadlock the parent + 6. M1 feeds the I2C transfer from step 1 to the root adapter as an + unlocked I2C transfer, so that it does not deadlock the parent adapter. 7. M1 calls ->deselect, if it has one. 8. Same rules as in step 5, but for ->deselect. 9. M1 unlocks its parent adapter. 10. M1 unlocks muxes on its parent. - This means that accesses to both D2 and D3 are locked out for the full duration of the entire operation. +Parent-locked Caveats +~~~~~~~~~~~~~~~~~~~~~ + +When using a parent-locked mux, be aware of the following restrictions: + +[PL1] + If you build a topology with a parent-locked mux being the child + of another mux, this might break a possible assumption from the + child mux that the root adapter is unused between its select op + and the actual transfer (e.g. if the child mux is auto-closing + and the parent mux issues I2C transfers as part of its select). + This is especially the case if the parent mux is mux-locked, but + it may also happen if the parent mux is parent-locked. + +[PL2] + If select/deselect calls out to other subsystems such as gpio, + pinctrl, regmap or iio, it is essential that any I2C transfers + caused by these subsystems are unlocked. This can be convoluted to + accomplish, maybe even impossible if an acceptably clean solution + is sought. + Complex Examples ================ @@ -240,7 +210,7 @@ and specifically when M2 requests its parent to lock, M1 passes the buck to the root adapter). This topology is bad if M2 is an auto-closing mux and M1->select -issues any unlocked i2c transfers on the root adapter that may leak +issues any unlocked I2C transfers on the root adapter that may leak through and be seen by the M2 adapter, thus closing M2 prematurely. @@ -261,8 +231,10 @@ This is a good topology:: When device D1 is accessed, accesses to D2 are locked out for the full duration of the operation (muxes on the top child adapter of M1 are locked). But accesses to D3 and D4 are possibly interleaved at -any point. Accesses to D3 locks out D1 and D2, but accesses to D4 -are still possibly interleaved. +any point. + +Accesses to D3 locks out D1 and D2, but accesses to D4 are still possibly +interleaved. Mux-locked mux as parent of parent-locked mux @@ -286,14 +258,14 @@ point. This kind of topology is generally not suitable and should probably be avoided. The reason is that M2 probably assumes that there will -be no i2c transfers during its calls to ->select and ->deselect, and +be no I2C transfers during its calls to ->select and ->deselect, and if there are, any such transfers might appear on the slave side of M2 -as partial i2c transfers, i.e. garbage or worse. This might cause +as partial I2C transfers, i.e. garbage or worse. This might cause device lockups and/or other problems. The topology is especially troublesome if M2 is an auto-closing mux. In that case, any interleaved accesses to D4 might close M2 -prematurely, as might any i2c-transfers part of M1->select. +prematurely, as might any I2C transfers part of M1->select. But if M2 is not making the above stated assumption, and if M2 is not auto-closing, the topology is fine. @@ -394,3 +366,47 @@ This is a good topology:: When D1 or D2 are accessed, accesses to D3 and D4 are locked out while accesses to D5 may interleave. When D3 or D4 are accessed, accesses to all other devices are locked out. + + +Mux type of existing device drivers +=================================== + +Whether a device is mux-locked or parent-locked depends on its +implementation. The following list was correct at the time of writing: + +In drivers/i2c/muxes/: + +====================== ============================================= +i2c-arb-gpio-challenge Parent-locked +i2c-mux-gpio Normally parent-locked, mux-locked iff + all involved gpio pins are controlled by the + same I2C root adapter that they mux. +i2c-mux-gpmux Normally parent-locked, mux-locked iff + specified in device-tree. +i2c-mux-ltc4306 Mux-locked +i2c-mux-mlxcpld Parent-locked +i2c-mux-pca9541 Parent-locked +i2c-mux-pca954x Parent-locked +i2c-mux-pinctrl Normally parent-locked, mux-locked iff + all involved pinctrl devices are controlled + by the same I2C root adapter that they mux. +i2c-mux-reg Parent-locked +====================== ============================================= + +In drivers/iio/: + +====================== ============================================= +gyro/mpu3050 Mux-locked +imu/inv_mpu6050/ Mux-locked +====================== ============================================= + +In drivers/media/: + +======================= ============================================= +dvb-frontends/lgdt3306a Mux-locked +dvb-frontends/m88ds3103 Parent-locked +dvb-frontends/rtl2830 Parent-locked +dvb-frontends/rtl2832 Mux-locked +dvb-frontends/si2168 Mux-locked +usb/cx231xx/ Parent-locked +======================= ============================================= diff --git a/Documentation/i2c/i2c_bus.svg b/Documentation/i2c/i2c_bus.svg new file mode 100644 index 000000000000..3170de976373 --- /dev/null +++ b/Documentation/i2c/i2c_bus.svg @@ -0,0 +1,1341 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!-- Created with Inkscape (http://www.inkscape.org/) --> + +<svg + xmlns:dc="http://purl.org/dc/elements/1.1/" + xmlns:cc="http://creativecommons.org/ns#" + xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" + xmlns:svg="http://www.w3.org/2000/svg" + xmlns="http://www.w3.org/2000/svg" + xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd" + 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busses/index + i2c-topology + muxes/i2c-mux-gpio + i2c-sysfs + i2c-address-translators + +Writing device drivers +====================== + .. toctree:: :maxdepth: 1 + writing-clients dev-interface dma-considerations fault-codes functionality + +Debugging +========= + +.. toctree:: + :maxdepth: 1 + gpio-fault-injection - i2c-protocol i2c-stub - i2c-topology - instantiating-devices - old-module-parameters - slave-eeprom-backend + +Slave I2C +========= + +.. toctree:: + :maxdepth: 1 + slave-interface - smbus-protocol - summary + slave-eeprom-backend + slave-testunit-backend + +Advanced topics +=============== + +.. toctree:: + :maxdepth: 1 + ten-bit-addresses - upgrading-clients - writing-clients - muxes/i2c-mux-gpio +Legacy documentation +==================== - busses/index +.. toctree:: + :maxdepth: 1 + + old-module-parameters .. only:: subproject and html diff --git a/Documentation/i2c/instantiating-devices.rst b/Documentation/i2c/instantiating-devices.rst index 875ebe9e78e3..3ea056a95812 100644 --- a/Documentation/i2c/instantiating-devices.rst +++ b/Documentation/i2c/instantiating-devices.rst @@ -9,56 +9,31 @@ reason, the kernel code must instantiate I2C devices explicitly. There are several ways to achieve this, depending on the context and requirements. -Method 1a: Declare the I2C devices by bus number ------------------------------------------------- +Method 1: Declare the I2C devices statically +-------------------------------------------- This method is appropriate when the I2C bus is a system bus as is the case -for many embedded systems. On such systems, each I2C bus has a number -which is known in advance. It is thus possible to pre-declare the I2C -devices which live on this bus. This is done with an array of struct -i2c_board_info which is registered by calling i2c_register_board_info(). - -Example (from omap2 h4):: - - static struct i2c_board_info h4_i2c_board_info[] __initdata = { - { - I2C_BOARD_INFO("isp1301_omap", 0x2d), - .irq = OMAP_GPIO_IRQ(125), - }, - { /* EEPROM on mainboard */ - I2C_BOARD_INFO("24c01", 0x52), - .platform_data = &m24c01, - }, - { /* EEPROM on cpu card */ - I2C_BOARD_INFO("24c01", 0x57), - .platform_data = &m24c01, - }, - }; +for many embedded systems. On such systems, each I2C bus has a number which +is known in advance. It is thus possible to pre-declare the I2C devices +which live on this bus. - static void __init omap_h4_init(void) - { - (...) - i2c_register_board_info(1, h4_i2c_board_info, - ARRAY_SIZE(h4_i2c_board_info)); - (...) - } +This information is provided to the kernel in a different way on different +architectures: device tree, ACPI or board files. -The above code declares 3 devices on I2C bus 1, including their respective -addresses and custom data needed by their drivers. When the I2C bus in -question is registered, the I2C devices will be instantiated automatically -by i2c-core. +When the I2C bus in question is registered, the I2C devices will be +instantiated automatically by i2c-core. The devices will be automatically +unbound and destroyed when the I2C bus they sit on goes away (if ever). -The devices will be automatically unbound and destroyed when the I2C bus -they sit on goes away (if ever.) +Declare the I2C devices via devicetree +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -Method 1b: Declare the I2C devices via devicetree -------------------------------------------------- +On platforms using devicetree, the declaration of I2C devices is done in +subnodes of the master controller. -This method has the same implications as method 1a. The declaration of I2C -devices is here done via devicetree as subnodes of the master controller. +Example: -Example:: +.. code-block:: dts i2c1: i2c@400a0000 { /* ... master properties skipped ... */ @@ -82,13 +57,53 @@ additional properties which might be needed to set up the device, please refer to its devicetree documentation in Documentation/devicetree/bindings/. -Method 1c: Declare the I2C devices via ACPI -------------------------------------------- +Declare the I2C devices via ACPI +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ACPI can also describe I2C devices. There is special documentation for this which is currently located at Documentation/firmware-guide/acpi/enumeration.rst. +Declare the I2C devices in board files +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In many embedded architectures, devicetree has replaced the old hardware +description based on board files, but the latter are still used in old +code. Instantiating I2C devices via board files is done with an array of +struct i2c_board_info which is registered by calling +i2c_register_board_info(). + +Example (from omap2 h4): + +.. code-block:: c + + static struct i2c_board_info h4_i2c_board_info[] __initdata = { + { + I2C_BOARD_INFO("isp1301_omap", 0x2d), + .irq = OMAP_GPIO_IRQ(125), + }, + { /* EEPROM on mainboard */ + I2C_BOARD_INFO("24c01", 0x52), + .platform_data = &m24c01, + }, + { /* EEPROM on cpu card */ + I2C_BOARD_INFO("24c01", 0x57), + .platform_data = &m24c01, + }, + }; + + static void __init omap_h4_init(void) + { + (...) + i2c_register_board_info(1, h4_i2c_board_info, + ARRAY_SIZE(h4_i2c_board_info)); + (...) + } + +The above code declares 3 devices on I2C bus 1, including their respective +addresses and custom data needed by their drivers. + + Method 2: Instantiate the devices explicitly -------------------------------------------- @@ -98,9 +113,11 @@ tuner, a video decoder, an audio decoder, etc. usually connected to the main chip by the means of an I2C bus. You won't know the number of the I2C bus in advance, so the method 1 described above can't be used. Instead, you can instantiate your I2C devices explicitly. This is done by filling -a struct i2c_board_info and calling i2c_new_device(). +a struct i2c_board_info and calling i2c_new_client_device(). + +Example (from the sfe4001 network driver): -Example (from the sfe4001 network driver):: +.. code-block:: c static struct i2c_board_info sfe4001_hwmon_info = { I2C_BOARD_INFO("max6647", 0x4e), @@ -110,7 +127,7 @@ Example (from the sfe4001 network driver):: { (...) efx->board_info.hwmon_client = - i2c_new_device(&efx->i2c_adap, &sfe4001_hwmon_info); + i2c_new_client_device(&efx->i2c_adap, &sfe4001_hwmon_info); (...) } @@ -123,9 +140,11 @@ present or not (for example for an optional feature which is not present on cheap variants of a board but you have no way to tell them apart), or it may have different addresses from one board to the next (manufacturer changing its design without notice). In this case, you can call -i2c_new_scanned_device() instead of i2c_new_device(). +i2c_new_scanned_device() instead of i2c_new_client_device(). + +Example (from the nxp OHCI driver): -Example (from the nxp OHCI driver):: +.. code-block:: c static const unsigned short normal_i2c[] = { 0x2c, 0x2d, I2C_CLIENT_END }; @@ -152,7 +171,7 @@ simply gives up. The driver which instantiated the I2C device is responsible for destroying it on cleanup. This is done by calling i2c_unregister_device() on the -pointer that was earlier returned by i2c_new_device() or +pointer that was earlier returned by i2c_new_client_device() or i2c_new_scanned_device(). @@ -188,7 +207,7 @@ destroyed automatically when the driver which detected them is removed, or when the underlying I2C bus is itself destroyed, whichever happens first. -Those of you familiar with the i2c subsystem of 2.4 kernels and early 2.6 +Those of you familiar with the I2C subsystem of 2.4 kernels and early 2.6 kernels will find out that this method 3 is essentially similar to what was done there. Two significant differences are: @@ -214,15 +233,15 @@ In general, the kernel should know which I2C devices are connected and what addresses they live at. However, in certain cases, it does not, so a sysfs interface was added to let the user provide the information. This interface is made of 2 attribute files which are created in every I2C bus -directory: new_device and delete_device. Both files are write only and you -must write the right parameters to them in order to properly instantiate, -respectively delete, an I2C device. +directory: ``new_device`` and ``delete_device``. Both files are write +only and you must write the right parameters to them in order to properly +instantiate, respectively delete, an I2C device. -File new_device takes 2 parameters: the name of the I2C device (a string) -and the address of the I2C device (a number, typically expressed in -hexadecimal starting with 0x, but can also be expressed in decimal.) +File ``new_device`` takes 2 parameters: the name of the I2C device (a +string) and the address of the I2C device (a number, typically expressed +in hexadecimal starting with 0x, but can also be expressed in decimal.) -File delete_device takes a single parameter: the address of the I2C +File ``delete_device`` takes a single parameter: the address of the I2C device. As no two devices can live at the same address on a given I2C segment, the address is sufficient to uniquely identify the device to be deleted. diff --git a/Documentation/i2c/old-module-parameters.rst b/Documentation/i2c/old-module-parameters.rst index a1939512ad66..b08b6daabce9 100644 --- a/Documentation/i2c/old-module-parameters.rst +++ b/Documentation/i2c/old-module-parameters.rst @@ -1,19 +1,25 @@ -================================================= -I2C device driver binding control from user-space -================================================= +================================================================ +I2C device driver binding control from user-space in old kernels +================================================================ -Up to kernel 2.6.32, many i2c drivers used helper macros provided by +.. NOTE:: + Note: this section is only relevant if you are handling some old code + found in kernel 2.6. If you work with more recent kernels, you can + safely skip this section. + +Up to kernel 2.6.32, many I2C drivers used helper macros provided by <linux/i2c.h> which created standard module parameters to let the user -control how the driver would probe i2c buses and attach to devices. These -parameters were known as "probe" (to let the driver probe for an extra -address), "force" (to forcibly attach the driver to a given device) and -"ignore" (to prevent a driver from probing a given address). +control how the driver would probe I2C buses and attach to devices. These +parameters were known as ``probe`` (to let the driver probe for an extra +address), ``force`` (to forcibly attach the driver to a given device) and +``ignore`` (to prevent a driver from probing a given address). -With the conversion of the i2c subsystem to the standard device driver +With the conversion of the I2C subsystem to the standard device driver binding model, it became clear that these per-module parameters were no longer needed, and that a centralized implementation was possible. The new, -sysfs-based interface is described in the documentation file -"instantiating-devices", section "Method 4: Instantiate from user-space". +sysfs-based interface is described in +Documentation/i2c/instantiating-devices.rst, section +"Method 4: Instantiate from user-space". Below is a mapping from the old module parameters to the new interface. @@ -42,8 +48,8 @@ New method (sysfs interface):: # echo dummy 0x2f > /sys/bus/i2c/devices/i2c-1/new_device # modprobe <driver> -Of course, it is important to instantiate the "dummy" device before loading +Of course, it is important to instantiate the ``dummy`` device before loading the driver. The dummy device will be handled by i2c-core itself, preventing other drivers from binding to it later on. If there is a real device at the problematic address, and you want another driver to bind to it, then simply -pass the name of the device in question instead of "dummy". +pass the name of the device in question instead of ``dummy``. diff --git a/Documentation/i2c/slave-eeprom-backend.rst b/Documentation/i2c/slave-eeprom-backend.rst index 0b8cd83698e0..38d951f10302 100644 --- a/Documentation/i2c/slave-eeprom-backend.rst +++ b/Documentation/i2c/slave-eeprom-backend.rst @@ -1,14 +1,26 @@ ============================== -Linux I2C slave eeprom backend +Linux I2C slave EEPROM backend ============================== -by Wolfram Sang <wsa@sang-engineering.com> in 2014-15 +by Wolfram Sang <wsa@sang-engineering.com> in 2014-20 -This is a proof-of-concept backend which acts like an EEPROM on the connected -I2C bus. The memory contents can be modified from userspace via this file -located in sysfs:: +This backend simulates an EEPROM on the connected I2C bus. Its memory contents +can be accessed from userspace via this file located in sysfs:: /sys/bus/i2c/devices/<device-directory>/slave-eeprom +The following types are available: 24c02, 24c32, 24c64, and 24c512. Read-only +variants are also supported. The name needed for instantiating has the form +'slave-<type>[ro]'. Examples follow: + +24c02, read/write, address 0x64: + # echo slave-24c02 0x1064 > /sys/bus/i2c/devices/i2c-1/new_device + +24c512, read-only, address 0x42: + # echo slave-24c512ro 0x1042 > /sys/bus/i2c/devices/i2c-1/new_device + +You can also preload data during boot if a device-property named +'firmware-name' contains a valid filename (DT or ACPI only). + As of 2015, Linux doesn't support poll on binary sysfs files, so there is no notification when another master changed the content. diff --git a/Documentation/i2c/slave-interface.rst b/Documentation/i2c/slave-interface.rst index c769bd6a15bf..3f0d320bc80a 100644 --- a/Documentation/i2c/slave-interface.rst +++ b/Documentation/i2c/slave-interface.rst @@ -32,9 +32,9 @@ User manual =========== I2C slave backends behave like standard I2C clients. So, you can instantiate -them as described in the document 'instantiating-devices'. The only difference -is that i2c slave backends have their own address space. So, you have to add -0x1000 to the address you would originally request. An example for +them as described in the document instantiating-devices.rst. The only +difference is that i2c slave backends have their own address space. So, you +have to add 0x1000 to the address you would originally request. An example for instantiating the slave-eeprom driver from userspace at the 7 bit address 0x64 on bus 1:: @@ -59,7 +59,7 @@ The bus driver sends an event to the backend using the following function:: ret = i2c_slave_event(client, event, &val) -'client' describes the i2c slave device. 'event' is one of the special event +'client' describes the I2C slave device. 'event' is one of the special event types described hereafter. 'val' holds an u8 value for the data byte to be read/written and is thus bidirectional. The pointer to val must always be provided even if val is not used for an event, i.e. don't use NULL here. 'ret' @@ -72,12 +72,15 @@ Event types: 'val': unused - 'ret': always 0 + 'ret': 0 if the backend is ready, otherwise some errno Another I2C master wants to write data to us. This event should be sent once our own address and the write bit was detected. The data did not arrive yet, so -there is nothing to process or return. Wakeup or initialization probably needs -to be done, though. +there is nothing to process or return. After returning, the bus driver must +always ack the address phase. If 'ret' is zero, backend initialization or +wakeup is done and further data may be received. If 'ret' is an errno, the bus +driver should nack all incoming bytes until the next stop condition to enforce +a retry of the transmission. * I2C_SLAVE_READ_REQUESTED (mandatory) @@ -143,7 +146,7 @@ Bus driver support If you want to add slave support to the bus driver: * implement calls to register/unregister the slave and add those to the - struct i2c_algorithm. When registering, you probably need to set the i2c + struct i2c_algorithm. When registering, you probably need to set the I2C slave address and enable slave specific interrupts. If you use runtime pm, you should use pm_runtime_get_sync() because your device usually needs to be powered on always to be able to detect its slave address. When unregistering, diff --git a/Documentation/i2c/slave-testunit-backend.rst b/Documentation/i2c/slave-testunit-backend.rst new file mode 100644 index 000000000000..ecfc2abec32d --- /dev/null +++ b/Documentation/i2c/slave-testunit-backend.rst @@ -0,0 +1,88 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================ +Linux I2C slave testunit backend +================================ + +by Wolfram Sang <wsa@sang-engineering.com> in 2020 + +This backend can be used to trigger test cases for I2C bus masters which +require a remote device with certain capabilities (and which are usually not so +easy to obtain). Examples include multi-master testing, and SMBus Host Notify +testing. For some tests, the I2C slave controller must be able to switch +between master and slave mode because it needs to send data, too. + +Note that this is a device for testing and debugging. It should not be enabled +in a production build. And while there is some versioning and we try hard to +keep backward compatibility, there is no stable ABI guaranteed! + +Instantiating the device is regular. Example for bus 0, address 0x30: + +# echo "slave-testunit 0x1030" > /sys/bus/i2c/devices/i2c-0/new_device + +After that, you will have a write-only device listening. Reads will just return +an 8-bit version number of the testunit. When writing, the device consists of 4 +8-bit registers and, except for some "partial" commands, all registers must be +written to start a testcase, i.e. you usually write 4 bytes to the device. The +registers are: + +0x00 CMD - which test to trigger +0x01 DATAL - configuration byte 1 for the test +0x02 DATAH - configuration byte 2 for the test +0x03 DELAY - delay in n * 10ms until test is started + +Using 'i2cset' from the i2c-tools package, the generic command looks like: + +# i2cset -y <bus_num> <testunit_address> <CMD> <DATAL> <DATAH> <DELAY> i + +DELAY is a generic parameter which will delay the execution of the test in CMD. +While a command is running (including the delay), new commands will not be +acknowledged. You need to wait until the old one is completed. + +The commands are described in the following section. An invalid command will +result in the transfer not being acknowledged. + +Commands +-------- + +0x00 NOOP (reserved for future use) + +0x01 READ_BYTES (also needs master mode) + DATAL - address to read data from (lower 7 bits, highest bit currently unused) + DATAH - number of bytes to read + +This is useful to test if your bus master driver is handling multi-master +correctly. You can trigger the testunit to read bytes from another device on +the bus. If the bus master under test also wants to access the bus at the same +time, the bus will be busy. Example to read 128 bytes from device 0x50 after +50ms of delay: + +# i2cset -y 0 0x30 0x01 0x50 0x80 0x05 i + +0x02 SMBUS_HOST_NOTIFY (also needs master mode) + DATAL - low byte of the status word to send + DATAH - high byte of the status word to send + +This test will send an SMBUS_HOST_NOTIFY message to the host. Note that the +status word is currently ignored in the Linux Kernel. Example to send a +notification after 10ms: + +# i2cset -y 0 0x30 0x02 0x42 0x64 0x01 i + +0x03 SMBUS_BLOCK_PROC_CALL (partial command) + DATAL - must be '1', i.e. one further byte will be written + DATAH - number of bytes to be sent back + DELAY - not applicable, partial command! + +This test will respond to a block process call as defined by the SMBus +specification. The one data byte written specifies how many bytes will be sent +back in the following read transfer. Note that in this read transfer, the +testunit will prefix the length of the bytes to follow. So, if your host bus +driver emulates SMBus calls like the majority does, it needs to support the +I2C_M_RECV_LEN flag of an i2c_msg. This is a good testcase for it. The returned +data consists of the length first, and then of an array of bytes from length-1 +to 0. Here is an example which emulates i2c_smbus_block_process_call() using +i2ctransfer (you need i2c-tools v4.2 or later): + +# i2ctransfer -y 0 w3@0x30 0x03 0x01 0x10 r? +0x10 0x0f 0x0e 0x0d 0x0c 0x0b 0x0a 0x09 0x08 0x07 0x06 0x05 0x04 0x03 0x02 0x01 0x00 diff --git a/Documentation/i2c/smbus-protocol.rst b/Documentation/i2c/smbus-protocol.rst index e30eb1d274c6..adc87456c99d 100644 --- a/Documentation/i2c/smbus-protocol.rst +++ b/Documentation/i2c/smbus-protocol.rst @@ -1,6 +1,6 @@ -====================== -SMBus Protocol Summary -====================== +================== +The SMBus Protocol +================== The following is a summary of the SMBus protocol. It applies to all revisions of the protocol (1.0, 1.1, and 2.0). @@ -28,26 +28,28 @@ Each transaction type corresponds to a functionality flag. Before calling a transaction function, a device driver should always check (just once) for the corresponding functionality flag to ensure that the underlying I2C adapter supports the transaction in question. See -<file:Documentation/i2c/functionality.rst> for the details. +Documentation/i2c/functionality.rst for the details. Key to symbols ============== =============== ============================================================= -S (1 bit) : Start bit -P (1 bit) : Stop bit -Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0. -A, NA (1 bit) : Accept and reverse accept bit. -Addr (7 bits): I2C 7 bit address. Note that this can be expanded as usual to +S Start condition +Sr Repeated start condition, used to switch from write to + read mode. +P Stop condition +Rd/Wr (1 bit) Read/Write bit. Rd equals 1, Wr equals 0. +A, NA (1 bit) Acknowledge (ACK) and Not Acknowledge (NACK) bit +Addr (7 bits) I2C 7 bit address. Note that this can be expanded to get a 10 bit I2C address. -Comm (8 bits): Command byte, a data byte which often selects a register on +Comm (8 bits) Command byte, a data byte which often selects a register on the device. -Data (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh - for 16 bit data. -Count (8 bits): A data byte containing the length of a block operation. +Data (8 bits) A plain data byte. DataLow and DataHigh represent the low and + high byte of a 16 bit word. +Count (8 bits) A data byte containing the length of a block operation. -[..]: Data sent by I2C device, as opposed to data sent by the host +[..] Data sent by I2C device, as opposed to data sent by the host adapter. =============== ============================================================= @@ -57,13 +59,15 @@ SMBus Quick Command This sends a single bit to the device, at the place of the Rd/Wr bit:: - A Addr Rd/Wr [A] P + S Addr Rd/Wr [A] P Functionality flag: I2C_FUNC_SMBUS_QUICK -SMBus Receive Byte: i2c_smbus_read_byte() -========================================== +SMBus Receive Byte +================== + +Implemented by i2c_smbus_read_byte() This reads a single byte from a device, without specifying a device register. Some devices are so simple that this interface is enough; for @@ -75,8 +79,10 @@ the previous SMBus command:: Functionality flag: I2C_FUNC_SMBUS_READ_BYTE -SMBus Send Byte: i2c_smbus_write_byte() -======================================== +SMBus Send Byte +=============== + +Implemented by i2c_smbus_write_byte() This operation is the reverse of Receive Byte: it sends a single byte to a device. See Receive Byte for more information. @@ -88,35 +94,41 @@ to a device. See Receive Byte for more information. Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE -SMBus Read Byte: i2c_smbus_read_byte_data() -============================================ +SMBus Read Byte +=============== + +Implemented by i2c_smbus_read_byte_data() This reads a single byte from a device, from a designated register. The register is specified through the Comm byte:: - S Addr Wr [A] Comm [A] S Addr Rd [A] [Data] NA P + S Addr Wr [A] Comm [A] Sr Addr Rd [A] [Data] NA P Functionality flag: I2C_FUNC_SMBUS_READ_BYTE_DATA -SMBus Read Word: i2c_smbus_read_word_data() -============================================ +SMBus Read Word +=============== + +Implemented by i2c_smbus_read_word_data() This operation is very like Read Byte; again, data is read from a device, from a designated register that is specified through the Comm byte. But this time, the data is a complete word (16 bits):: - S Addr Wr [A] Comm [A] S Addr Rd [A] [DataLow] A [DataHigh] NA P + S Addr Wr [A] Comm [A] Sr Addr Rd [A] [DataLow] A [DataHigh] NA P Functionality flag: I2C_FUNC_SMBUS_READ_WORD_DATA -Note the convenience function i2c_smbus_read_word_swapped is +Note the convenience function i2c_smbus_read_word_swapped() is available for reads where the two data bytes are the other way around (not SMBus compliant, but very popular.) -SMBus Write Byte: i2c_smbus_write_byte_data() -============================================== +SMBus Write Byte +================ + +Implemented by i2c_smbus_write_byte_data() This writes a single byte to a device, to a designated register. The register is specified through the Comm byte. This is the opposite of @@ -129,36 +141,40 @@ the Read Byte operation. Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE_DATA -SMBus Write Word: i2c_smbus_write_word_data() -============================================== +SMBus Write Word +================ + +Implemented by i2c_smbus_write_word_data() This is the opposite of the Read Word operation. 16 bits -of data is written to a device, to the designated register that is -specified through the Comm byte.:: +of data are written to a device, to the designated register that is +specified through the Comm byte:: S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P Functionality flag: I2C_FUNC_SMBUS_WRITE_WORD_DATA -Note the convenience function i2c_smbus_write_word_swapped is +Note the convenience function i2c_smbus_write_word_swapped() is available for writes where the two data bytes are the other way around (not SMBus compliant, but very popular.) -SMBus Process Call: -=================== +SMBus Process Call +================== This command selects a device register (through the Comm byte), sends 16 bits of data to it, and reads 16 bits of data in return:: S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] - S Addr Rd [A] [DataLow] A [DataHigh] NA P + Sr Addr Rd [A] [DataLow] A [DataHigh] NA P Functionality flag: I2C_FUNC_SMBUS_PROC_CALL -SMBus Block Read: i2c_smbus_read_block_data() -============================================== +SMBus Block Read +================ + +Implemented by i2c_smbus_read_block_data() This command reads a block of up to 32 bytes from a device, from a designated register that is specified through the Comm byte. The amount @@ -167,13 +183,15 @@ of data is specified by the device in the Count byte. :: S Addr Wr [A] Comm [A] - S Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P + Sr Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P Functionality flag: I2C_FUNC_SMBUS_READ_BLOCK_DATA -SMBus Block Write: i2c_smbus_write_block_data() -================================================ +SMBus Block Write +================= + +Implemented by i2c_smbus_write_block_data() The opposite of the Block Read command, this writes up to 32 bytes to a device, to a designated register that is specified through the @@ -196,7 +214,7 @@ This command selects a device register (through the Comm byte), sends 1 to 31 bytes of data to it, and reads 1 to 31 bytes of data in return:: S Addr Wr [A] Comm [A] Count [A] Data [A] ... - S Addr Rd [A] [Count] A [Data] ... A P + Sr Addr Rd [A] [Count] A [Data] ... A P Functionality flag: I2C_FUNC_SMBUS_BLOCK_PROC_CALL @@ -220,7 +238,7 @@ This is implemented in the following way in the Linux kernel: * I2C bus drivers trigger SMBus Host Notify by a call to i2c_handle_smbus_host_notify(). * I2C drivers for devices which can trigger SMBus Host Notify will have - client->irq assigned to a Host Notify IRQ if noone else specified an other. + client->irq assigned to a Host Notify IRQ if no one else specified another. There is currently no way to retrieve the data parameter from the client. @@ -258,7 +276,7 @@ to know which slave triggered the interrupt. This is implemented the following way in the Linux kernel: * I2C bus drivers which support SMBus alert should call - i2c_setup_smbus_alert() to setup SMBus alert support. + i2c_new_smbus_alert_device() to install SMBus alert support. * I2C drivers for devices which can trigger SMBus alerts should implement the optional alert() callback. @@ -266,28 +284,33 @@ This is implemented the following way in the Linux kernel: I2C Block Transactions ====================== -The following I2C block transactions are supported by the -SMBus layer and are described here for completeness. -They are *NOT* defined by the SMBus specification. +The following I2C block transactions are similar to the SMBus Block Read +and Write operations, except these do not have a Count byte. They are +supported by the SMBus layer and are described here for completeness, but +they are *NOT* defined by the SMBus specification. I2C block transactions do not limit the number of bytes transferred but the SMBus layer places a limit of 32 bytes. -I2C Block Read: i2c_smbus_read_i2c_block_data() -================================================ +I2C Block Read +============== + +Implemented by i2c_smbus_read_i2c_block_data() This command reads a block of bytes from a device, from a designated register that is specified through the Comm byte:: S Addr Wr [A] Comm [A] - S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P + Sr Addr Rd [A] [Data] A [Data] A ... A [Data] NA P Functionality flag: I2C_FUNC_SMBUS_READ_I2C_BLOCK -I2C Block Write: i2c_smbus_write_i2c_block_data() -================================================== +I2C Block Write +=============== + +Implemented by i2c_smbus_write_i2c_block_data() The opposite of the Block Read command, this writes bytes to a device, to a designated register that is specified through the diff --git a/Documentation/i2c/summary.rst b/Documentation/i2c/summary.rst index 3a24eac17375..786c618ba3be 100644 --- a/Documentation/i2c/summary.rst +++ b/Documentation/i2c/summary.rst @@ -1,13 +1,21 @@ -============= -I2C and SMBus -============= - -I2C (pronounce: I squared C) is a protocol developed by Philips. It is a -slow two-wire protocol (variable speed, up to 400 kHz), with a high speed -extension (3.4 MHz). It provides an inexpensive bus for connecting many -types of devices with infrequent or low bandwidth communications needs. -I2C is widely used with embedded systems. Some systems use variants that -don't meet branding requirements, and so are not advertised as being I2C. +============================= +Introduction to I2C and SMBus +============================= + +I²C (pronounce: I squared C and written I2C in the kernel documentation) is +a protocol developed by Philips. It is a slow two-wire protocol (variable +speed, up to 400 kHz), with a high speed extension (3.4 MHz). It provides +an inexpensive bus for connecting many types of devices with infrequent or +low bandwidth communications needs. I2C is widely used with embedded +systems. Some systems use variants that don't meet branding requirements, +and so are not advertised as being I2C but come under different names, +e.g. TWI (Two Wire Interface), IIC. + +The latest official I2C specification is the `"I2C-bus specification and user +manual" (UM10204) <https://www.nxp.com/webapp/Download?colCode=UM10204>`_ +published by NXP Semiconductors. However, you need to log-in to the site to +access the PDF. An older version of the specification (revision 6) is archived +`here <https://web.archive.org/web/20210813122132/https://www.nxp.com/docs/en/user-guide/UM10204.pdf>`_. SMBus (System Management Bus) is based on the I2C protocol, and is mostly a subset of I2C protocols and signaling. Many I2C devices will work on an @@ -25,21 +33,29 @@ implement all the common SMBus protocol semantics or messages. Terminology =========== -When we talk about I2C, we use the following terms:: +Using the terminology from the official documentation, the I2C bus connects +one or more *master* chips and one or more *slave* chips. + +.. kernel-figure:: i2c_bus.svg + :alt: Simple I2C bus with one master and 3 slaves + + Simple I2C bus - Bus -> Algorithm - Adapter - Device -> Driver - Client +A **master** chip is a node that starts communications with slaves. In the +Linux kernel implementation it is called an **adapter** or bus. Adapter +drivers are in the ``drivers/i2c/busses/`` subdirectory. -An Algorithm driver contains general code that can be used for a whole class -of I2C adapters. Each specific adapter driver either depends on one algorithm -driver, or includes its own implementation. +An **algorithm** contains general code that can be used to implement a +whole class of I2C adapters. Each specific adapter driver either depends on +an algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes +its own implementation. -A Driver driver (yes, this sounds ridiculous, sorry) contains the general -code to access some type of device. Each detected device gets its own -data in the Client structure. Usually, Driver and Client are more closely -integrated than Algorithm and Adapter. +A **slave** chip is a node that responds to communications when addressed +by the master. In Linux it is called a **client**. Client drivers are kept +in a directory specific to the feature they provide, for example +``drivers/media/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for +video-related chips. -For a given configuration, you will need a driver for your I2C bus, and -drivers for your I2C devices (usually one driver for each device). +For the example configuration in figure, you will need a driver for your +I2C adapter, and drivers for your I2C devices (usually one driver for each +device). diff --git a/Documentation/i2c/upgrading-clients.rst b/Documentation/i2c/upgrading-clients.rst deleted file mode 100644 index 27d29032c138..000000000000 --- a/Documentation/i2c/upgrading-clients.rst +++ /dev/null @@ -1,285 +0,0 @@ -================================================= -Upgrading I2C Drivers to the new 2.6 Driver Model -================================================= - -Ben Dooks <ben-linux@fluff.org> - -Introduction ------------- - -This guide outlines how to alter existing Linux 2.6 client drivers from -the old to the new new binding methods. - - -Example old-style driver ------------------------- - -:: - - struct example_state { - struct i2c_client client; - .... - }; - - static struct i2c_driver example_driver; - - static unsigned short ignore[] = { I2C_CLIENT_END }; - static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END }; - - I2C_CLIENT_INSMOD; - - static int example_attach(struct i2c_adapter *adap, int addr, int kind) - { - struct example_state *state; - struct device *dev = &adap->dev; /* to use for dev_ reports */ - int ret; - - state = kzalloc(sizeof(struct example_state), GFP_KERNEL); - if (state == NULL) { - dev_err(dev, "failed to create our state\n"); - return -ENOMEM; - } - - example->client.addr = addr; - example->client.flags = 0; - example->client.adapter = adap; - - i2c_set_clientdata(&state->i2c_client, state); - strscpy(client->i2c_client.name, "example", sizeof(client->i2c_client.name)); - - ret = i2c_attach_client(&state->i2c_client); - if (ret < 0) { - dev_err(dev, "failed to attach client\n"); - kfree(state); - return ret; - } - - dev = &state->i2c_client.dev; - - /* rest of the initialisation goes here. */ - - dev_info(dev, "example client created\n"); - - return 0; - } - - static int example_detach(struct i2c_client *client) - { - struct example_state *state = i2c_get_clientdata(client); - - i2c_detach_client(client); - kfree(state); - return 0; - } - - static int example_attach_adapter(struct i2c_adapter *adap) - { - return i2c_probe(adap, &addr_data, example_attach); - } - - static struct i2c_driver example_driver = { - .driver = { - .owner = THIS_MODULE, - .name = "example", - .pm = &example_pm_ops, - }, - .attach_adapter = example_attach_adapter, - .detach_client = example_detach, - }; - - -Updating the client -------------------- - -The new style binding model will check against a list of supported -devices and their associated address supplied by the code registering -the busses. This means that the driver .attach_adapter and -.detach_client methods can be removed, along with the addr_data, -as follows:: - - - static struct i2c_driver example_driver; - - - static unsigned short ignore[] = { I2C_CLIENT_END }; - - static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END }; - - - I2C_CLIENT_INSMOD; - - - static int example_attach_adapter(struct i2c_adapter *adap) - - { - - return i2c_probe(adap, &addr_data, example_attach); - - } - - static struct i2c_driver example_driver = { - - .attach_adapter = example_attach_adapter, - - .detach_client = example_detach, - } - -Add the probe and remove methods to the i2c_driver, as so:: - - static struct i2c_driver example_driver = { - + .probe = example_probe, - + .remove = example_remove, - } - -Change the example_attach method to accept the new parameters -which include the i2c_client that it will be working with:: - - - static int example_attach(struct i2c_adapter *adap, int addr, int kind) - + static int example_probe(struct i2c_client *client, - + const struct i2c_device_id *id) - -Change the name of example_attach to example_probe to align it with the -i2c_driver entry names. The rest of the probe routine will now need to be -changed as the i2c_client has already been setup for use. - -The necessary client fields have already been setup before -the probe function is called, so the following client setup -can be removed:: - - - example->client.addr = addr; - - example->client.flags = 0; - - example->client.adapter = adap; - - - - strscpy(client->i2c_client.name, "example", sizeof(client->i2c_client.name)); - -The i2c_set_clientdata is now:: - - - i2c_set_clientdata(&state->client, state); - + i2c_set_clientdata(client, state); - -The call to i2c_attach_client is no longer needed, if the probe -routine exits successfully, then the driver will be automatically -attached by the core. Change the probe routine as so:: - - - ret = i2c_attach_client(&state->i2c_client); - - if (ret < 0) { - - dev_err(dev, "failed to attach client\n"); - - kfree(state); - - return ret; - - } - - -Remove the storage of 'struct i2c_client' from the 'struct example_state' -as we are provided with the i2c_client in our example_probe. Instead we -store a pointer to it for when it is needed. - -:: - - struct example_state { - - struct i2c_client client; - + struct i2c_client *client; - -the new i2c client as so:: - - - struct device *dev = &adap->dev; /* to use for dev_ reports */ - + struct device *dev = &i2c_client->dev; /* to use for dev_ reports */ - -And remove the change after our client is attached, as the driver no -longer needs to register a new client structure with the core:: - - - dev = &state->i2c_client.dev; - -In the probe routine, ensure that the new state has the client stored -in it:: - - static int example_probe(struct i2c_client *i2c_client, - const struct i2c_device_id *id) - { - struct example_state *state; - struct device *dev = &i2c_client->dev; - int ret; - - state = kzalloc(sizeof(struct example_state), GFP_KERNEL); - if (state == NULL) { - dev_err(dev, "failed to create our state\n"); - return -ENOMEM; - } - - + state->client = i2c_client; - -Update the detach method, by changing the name to _remove and -to delete the i2c_detach_client call. It is possible that you -can also remove the ret variable as it is not needed for any -of the core functions. - -:: - - - static int example_detach(struct i2c_client *client) - + static int example_remove(struct i2c_client *client) - { - struct example_state *state = i2c_get_clientdata(client); - - - i2c_detach_client(client); - -And finally ensure that we have the correct ID table for the i2c-core -and other utilities:: - - + struct i2c_device_id example_idtable[] = { - + { "example", 0 }, - + { } - +}; - + - +MODULE_DEVICE_TABLE(i2c, example_idtable); - - static struct i2c_driver example_driver = { - .driver = { - .owner = THIS_MODULE, - .name = "example", - }, - + .id_table = example_ids, - - -Our driver should now look like this:: - - struct example_state { - struct i2c_client *client; - .... - }; - - static int example_probe(struct i2c_client *client, - const struct i2c_device_id *id) - { - struct example_state *state; - struct device *dev = &client->dev; - - state = kzalloc(sizeof(struct example_state), GFP_KERNEL); - if (state == NULL) { - dev_err(dev, "failed to create our state\n"); - return -ENOMEM; - } - - state->client = client; - i2c_set_clientdata(client, state); - - /* rest of the initialisation goes here. */ - - dev_info(dev, "example client created\n"); - - return 0; - } - - static int example_remove(struct i2c_client *client) - { - struct example_state *state = i2c_get_clientdata(client); - - kfree(state); - return 0; - } - - static struct i2c_device_id example_idtable[] = { - { "example", 0 }, - { } - }; - - MODULE_DEVICE_TABLE(i2c, example_idtable); - - static struct i2c_driver example_driver = { - .driver = { - .owner = THIS_MODULE, - .name = "example", - .pm = &example_pm_ops, - }, - .id_table = example_idtable, - .probe = example_probe, - .remove = example_remove, - }; diff --git a/Documentation/i2c/writing-clients.rst b/Documentation/i2c/writing-clients.rst index ced309b5e0cc..41ddc10f1ac7 100644 --- a/Documentation/i2c/writing-clients.rst +++ b/Documentation/i2c/writing-clients.rst @@ -1,6 +1,6 @@ -=================== -Writing I2C Clients -=================== +=============================== +Implementing I2C device drivers +=============================== This is a small guide for those who want to write kernel drivers for I2C or SMBus devices, using Linux as the protocol host/master (not slave). @@ -95,7 +95,7 @@ to gather information from the client, or write new information to the client. I have found it useful to define foo_read and foo_write functions for this. -For some cases, it will be easier to call the i2c functions directly, +For some cases, it will be easier to call the I2C functions directly, but many chips have some kind of register-value idea that can easily be encapsulated. @@ -155,9 +155,8 @@ those devices, and a remove() method to unbind. :: - static int foo_probe(struct i2c_client *client, - const struct i2c_device_id *id); - static int foo_remove(struct i2c_client *client); + static int foo_probe(struct i2c_client *client); + static void foo_remove(struct i2c_client *client); Remember that the i2c_driver does not create those client handles. The handle may be used during foo_probe(). If foo_probe() reports success @@ -165,8 +164,12 @@ handle may be used during foo_probe(). If foo_probe() reports success foo_remove() returns. That binding model is used by most Linux drivers. The probe function is called when an entry in the id_table name field -matches the device's name. It is passed the entry that was matched so -the driver knows which one in the table matched. +matches the device's name. If the probe function needs that entry, it +can retrieve it using + +:: + + const struct i2c_device_id *id = i2c_match_id(foo_idtable, client); Device Creation @@ -175,8 +178,8 @@ Device Creation If you know for a fact that an I2C device is connected to a given I2C bus, you can instantiate that device by simply filling an i2c_board_info structure with the device address and driver name, and calling -i2c_new_device(). This will create the device, then the driver core will -take care of finding the right driver and will call its probe() method. +i2c_new_client_device(). This will create the device, then the driver core +will take care of finding the right driver and will call its probe() method. If a driver supports different device types, you can specify the type you want using the type field. You can also specify an IRQ and platform data if needed. @@ -186,14 +189,14 @@ don't know the exact address it uses. This happens on TV adapters for example, where the same driver supports dozens of slightly different models, and I2C device addresses change from one model to the next. In that case, you can use the i2c_new_scanned_device() variant, which is -similar to i2c_new_device(), except that it takes an additional list of -possible I2C addresses to probe. A device is created for the first +similar to i2c_new_client_device(), except that it takes an additional list +of possible I2C addresses to probe. A device is created for the first responsive address in the list. If you expect more than one device to be present in the address range, simply call i2c_new_scanned_device() that many times. -The call to i2c_new_device() or i2c_new_scanned_device() typically happens -in the I2C bus driver. You may want to save the returned i2c_client +The call to i2c_new_client_device() or i2c_new_scanned_device() typically +happens in the I2C bus driver. You may want to save the returned i2c_client reference for later use. @@ -236,11 +239,11 @@ possible. Device Deletion --------------- -Each I2C device which has been created using i2c_new_device() or -i2c_new_scanned_device() can be unregistered by calling +Each I2C device which has been created using i2c_new_client_device() +or i2c_new_scanned_device() can be unregistered by calling i2c_unregister_device(). If you don't call it explicitly, it will be -called automatically before the underlying I2C bus itself is removed, as a -device can't survive its parent in the device driver model. +called automatically before the underlying I2C bus itself is removed, +as a device can't survive its parent in the device driver model. Initializing the driver @@ -344,7 +347,7 @@ Plain I2C communication int i2c_master_recv(struct i2c_client *client, char *buf, int count); These routines read and write some bytes from/to a client. The client -contains the i2c address, so you do not have to include it. The second +contains the I2C address, so you do not have to include it. The second parameter contains the bytes to read/write, the third the number of bytes to read/write (must be less than the length of the buffer, also should be less than 64k since msg.len is u16.) Returned is the actual number of bytes @@ -357,11 +360,11 @@ read/written. This sends a series of messages. Each message can be a read or write, and they can be mixed in any way. The transactions are combined: no -stop bit is sent between transaction. The i2c_msg structure contains -for each message the client address, the number of bytes of the message -and the message data itself. +stop condition is issued between transaction. The i2c_msg structure +contains for each message the client address, the number of bytes of the +message and the message data itself. -You can read the file ``i2c-protocol`` for more information about the +You can read the file i2c-protocol.rst for more information about the actual I2C protocol. @@ -411,7 +414,7 @@ transactions return 0 on success; the 'read' transactions return the read value, except for block transactions, which return the number of values read. The block buffers need not be longer than 32 bytes. -You can read the file ``smbus-protocol`` for more information about the +You can read the file smbus-protocol.rst for more information about the actual SMBus protocol. |
