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Diffstat (limited to 'Documentation/i2c/dev-interface.rst')
| -rw-r--r-- | Documentation/i2c/dev-interface.rst | 28 |
1 files changed, 15 insertions, 13 deletions
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); |