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Diffstat (limited to 'Documentation/i2c/writing-clients.rst')
| -rw-r--r-- | Documentation/i2c/writing-clients.rst | 53 |
1 files changed, 28 insertions, 25 deletions
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. |