2005-04-17 00:20:36 +02:00
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This is a small guide for those who want to write kernel drivers for I2C
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2007-05-01 23:26:31 +02:00
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or SMBus devices, using Linux as the protocol host/master (not slave).
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2005-04-17 00:20:36 +02:00
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To set up a driver, you need to do several things. Some are optional, and
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some things can be done slightly or completely different. Use this as a
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guide, not as a rule book!
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General remarks
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===============
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Try to keep the kernel namespace as clean as possible. The best way to
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do this is to use a unique prefix for all global symbols. This is
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especially important for exported symbols, but it is a good idea to do
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it for non-exported symbols too. We will use the prefix `foo_' in this
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tutorial, and `FOO_' for preprocessor variables.
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The driver structure
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====================
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Usually, you will implement a single driver structure, and instantiate
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all clients from it. Remember, a driver structure contains general access
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2007-02-13 22:09:00 +01:00
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routines, and should be zero-initialized except for fields with data you
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provide. A client structure holds device-specific information like the
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driver model device node, and its I2C address.
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2005-04-17 00:20:36 +02:00
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static struct i2c_driver foo_driver = {
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2005-11-26 20:55:35 +01:00
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.driver = {
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.name = "foo",
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},
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2007-05-01 23:26:31 +02:00
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/* iff driver uses driver model ("new style") binding model: */
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.probe = foo_probe,
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.remove = foo_remove,
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/* else, driver uses "legacy" binding model: */
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2007-02-13 22:09:00 +01:00
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.attach_adapter = foo_attach_adapter,
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.detach_client = foo_detach_client,
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2007-05-01 23:26:31 +02:00
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/* these may be used regardless of the driver binding model */
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2007-02-13 22:09:00 +01:00
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.shutdown = foo_shutdown, /* optional */
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.suspend = foo_suspend, /* optional */
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.resume = foo_resume, /* optional */
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.command = foo_command, /* optional */
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2005-04-17 00:20:36 +02:00
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}
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2007-02-13 22:09:00 +01:00
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The name field is the driver name, and must not contain spaces. It
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should match the module name (if the driver can be compiled as a module),
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although you can use MODULE_ALIAS (passing "foo" in this example) to add
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2007-05-01 23:26:31 +02:00
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another name for the module. If the driver name doesn't match the module
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name, the module won't be automatically loaded (hotplug/coldplug).
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2005-04-17 00:20:36 +02:00
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All other fields are for call-back functions which will be explained
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below.
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Extra client data
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=================
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2007-02-13 22:09:00 +01:00
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Each client structure has a special `data' field that can point to any
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structure at all. You should use this to keep device-specific data,
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especially in drivers that handle multiple I2C or SMBUS devices. You
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2005-04-17 00:20:36 +02:00
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do not always need this, but especially for `sensors' drivers, it can
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be very useful.
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2007-02-13 22:09:00 +01:00
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/* store the value */
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void i2c_set_clientdata(struct i2c_client *client, void *data);
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/* retrieve the value */
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void *i2c_get_clientdata(struct i2c_client *client);
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2005-04-17 00:20:36 +02:00
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An example structure is below.
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struct foo_data {
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2005-10-17 23:16:25 +02:00
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struct i2c_client client;
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2005-04-17 00:20:36 +02:00
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enum chips type; /* To keep the chips type for `sensors' drivers. */
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/* Because the i2c bus is slow, it is often useful to cache the read
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information of a chip for some time (for example, 1 or 2 seconds).
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It depends of course on the device whether this is really worthwhile
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or even sensible. */
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2007-05-01 23:26:35 +02:00
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struct mutex update_lock; /* When we are reading lots of information,
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2005-04-17 00:20:36 +02:00
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another process should not update the
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below information */
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char valid; /* != 0 if the following fields are valid. */
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unsigned long last_updated; /* In jiffies */
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/* Add the read information here too */
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};
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Accessing the client
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====================
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Let's say we have a valid client structure. At some time, we will need
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to gather information from the client, or write new information to the
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client. How we will export this information to user-space is less
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important at this moment (perhaps we do not need to do this at all for
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some obscure clients). But we need generic reading and writing routines.
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I have found it useful to define foo_read and foo_write function for this.
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For some cases, it will be easier to call the i2c functions directly,
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but many chips have some kind of register-value idea that can easily
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2007-05-01 23:26:35 +02:00
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be encapsulated.
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2005-04-17 00:20:36 +02:00
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The below functions are simple examples, and should not be copied
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literally.
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int foo_read_value(struct i2c_client *client, u8 reg)
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{
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if (reg < 0x10) /* byte-sized register */
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return i2c_smbus_read_byte_data(client,reg);
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else /* word-sized register */
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return i2c_smbus_read_word_data(client,reg);
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}
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int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
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{
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if (reg == 0x10) /* Impossible to write - driver error! */ {
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return -1;
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else if (reg < 0x10) /* byte-sized register */
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return i2c_smbus_write_byte_data(client,reg,value);
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else /* word-sized register */
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return i2c_smbus_write_word_data(client,reg,value);
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}
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Probing and attaching
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=====================
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2007-05-01 23:26:31 +02:00
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The Linux I2C stack was originally written to support access to hardware
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monitoring chips on PC motherboards, and thus it embeds some assumptions
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that are more appropriate to SMBus (and PCs) than to I2C. One of these
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assumptions is that most adapters and devices drivers support the SMBUS_QUICK
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protocol to probe device presence. Another is that devices and their drivers
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can be sufficiently configured using only such probe primitives.
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As Linux and its I2C stack became more widely used in embedded systems
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and complex components such as DVB adapters, those assumptions became more
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problematic. Drivers for I2C devices that issue interrupts need more (and
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different) configuration information, as do drivers handling chip variants
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that can't be distinguished by protocol probing, or which need some board
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specific information to operate correctly.
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Accordingly, the I2C stack now has two models for associating I2C devices
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with their drivers: the original "legacy" model, and a newer one that's
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fully compatible with the Linux 2.6 driver model. These models do not mix,
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since the "legacy" model requires drivers to create "i2c_client" device
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objects after SMBus style probing, while the Linux driver model expects
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drivers to be given such device objects in their probe() routines.
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Standard Driver Model Binding ("New Style")
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-------------------------------------------
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System infrastructure, typically board-specific initialization code or
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boot firmware, reports what I2C devices exist. For example, there may be
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a table, in the kernel or from the boot loader, identifying I2C devices
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and linking them to board-specific configuration information about IRQs
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and other wiring artifacts, chip type, and so on. That could be used to
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create i2c_client objects for each I2C device.
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I2C device drivers using this binding model work just like any other
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kind of driver in Linux: they provide a probe() method to bind to
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those devices, and a remove() method to unbind.
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static int foo_probe(struct i2c_client *client);
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static int foo_remove(struct i2c_client *client);
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Remember that the i2c_driver does not create those client handles. The
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handle may be used during foo_probe(). If foo_probe() reports success
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(zero not a negative status code) it may save the handle and use it until
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foo_remove() returns. That binding model is used by most Linux drivers.
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Drivers match devices when i2c_client.driver_name and the driver name are
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the same; this approach is used in several other busses that don't have
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device typing support in the hardware. The driver and module name should
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match, so hotplug/coldplug mechanisms will modprobe the driver.
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2007-05-01 23:26:32 +02:00
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Device Creation (Standard driver model)
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---------------------------------------
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If you know for a fact that an I2C device is connected to a given I2C bus,
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you can instantiate that device by simply filling an i2c_board_info
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structure with the device address and driver name, and calling
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i2c_new_device(). This will create the device, then the driver core will
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take care of finding the right driver and will call its probe() method.
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If a driver supports different device types, you can specify the type you
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want using the type field. You can also specify an IRQ and platform data
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if needed.
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Sometimes you know that a device is connected to a given I2C bus, but you
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don't know the exact address it uses. This happens on TV adapters for
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example, where the same driver supports dozens of slightly different
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models, and I2C device addresses change from one model to the next. In
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that case, you can use the i2c_new_probed_device() variant, which is
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similar to i2c_new_device(), except that it takes an additional list of
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possible I2C addresses to probe. A device is created for the first
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responsive address in the list. If you expect more than one device to be
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present in the address range, simply call i2c_new_probed_device() that
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many times.
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The call to i2c_new_device() or i2c_new_probed_device() typically happens
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in the I2C bus driver. You may want to save the returned i2c_client
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reference for later use.
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Device Deletion (Standard driver model)
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---------------------------------------
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Each I2C device which has been created using i2c_new_device() or
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i2c_new_probed_device() can be unregistered by calling
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i2c_unregister_device(). If you don't call it explicitly, it will be
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called automatically before the underlying I2C bus itself is removed, as a
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device can't survive its parent in the device driver model.
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2007-05-01 23:26:31 +02:00
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Legacy Driver Binding Model
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---------------------------
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2005-04-17 00:20:36 +02:00
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Most i2c devices can be present on several i2c addresses; for some this
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is determined in hardware (by soldering some chip pins to Vcc or Ground),
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for others this can be changed in software (by writing to specific client
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registers). Some devices are usually on a specific address, but not always;
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and some are even more tricky. So you will probably need to scan several
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i2c addresses for your clients, and do some sort of detection to see
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whether it is actually a device supported by your driver.
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To give the user a maximum of possibilities, some default module parameters
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are defined to help determine what addresses are scanned. Several macros
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are defined in i2c.h to help you support them, as well as a generic
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detection algorithm.
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You do not have to use this parameter interface; but don't try to use
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2005-07-31 21:42:02 +02:00
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function i2c_probe() if you don't.
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2005-04-17 00:20:36 +02:00
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2007-05-01 23:26:31 +02:00
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Probing classes (Legacy model)
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------------------------------
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2005-04-17 00:20:36 +02:00
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All parameters are given as lists of unsigned 16-bit integers. Lists are
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terminated by I2C_CLIENT_END.
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The following lists are used internally:
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normal_i2c: filled in by the module writer.
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A list of I2C addresses which should normally be examined.
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probe: insmod parameter.
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A list of pairs. The first value is a bus number (-1 for any I2C bus),
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the second is the address. These addresses are also probed, as if they
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were in the 'normal' list.
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ignore: insmod parameter.
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A list of pairs. The first value is a bus number (-1 for any I2C bus),
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the second is the I2C address. These addresses are never probed.
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2005-07-31 21:49:03 +02:00
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This parameter overrules the 'normal_i2c' list only.
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2005-04-17 00:20:36 +02:00
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force: insmod parameter.
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A list of pairs. The first value is a bus number (-1 for any I2C bus),
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the second is the I2C address. A device is blindly assumed to be on
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the given address, no probing is done.
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2005-07-31 21:49:03 +02:00
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Additionally, kind-specific force lists may optionally be defined if
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the driver supports several chip kinds. They are grouped in a
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NULL-terminated list of pointers named forces, those first element if the
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generic force list mentioned above. Each additional list correspond to an
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insmod parameter of the form force_<kind>.
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2005-04-02 20:31:02 +02:00
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Fortunately, as a module writer, you just have to define the `normal_i2c'
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parameter. The complete declaration could look like this:
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2005-04-17 00:20:36 +02:00
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2005-04-02 20:31:02 +02:00
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/* Scan 0x37, and 0x48 to 0x4f */
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static unsigned short normal_i2c[] = { 0x37, 0x48, 0x49, 0x4a, 0x4b, 0x4c,
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0x4d, 0x4e, 0x4f, I2C_CLIENT_END };
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2005-04-17 00:20:36 +02:00
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/* Magic definition of all other variables and things */
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I2C_CLIENT_INSMOD;
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2005-07-31 21:49:03 +02:00
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/* Or, if your driver supports, say, 2 kind of devices: */
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I2C_CLIENT_INSMOD_2(foo, bar);
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If you use the multi-kind form, an enum will be defined for you:
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enum chips { any_chip, foo, bar, ... }
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You can then (and certainly should) use it in the driver code.
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2005-04-17 00:20:36 +02:00
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2005-04-02 20:31:02 +02:00
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Note that you *have* to call the defined variable `normal_i2c',
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without any prefix!
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2005-04-17 00:20:36 +02:00
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2007-05-01 23:26:31 +02:00
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Attaching to an adapter (Legacy model)
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--------------------------------------
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2005-04-17 00:20:36 +02:00
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Whenever a new adapter is inserted, or for all adapters if the driver is
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being registered, the callback attach_adapter() is called. Now is the
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time to determine what devices are present on the adapter, and to register
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a client for each of them.
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The attach_adapter callback is really easy: we just call the generic
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detection function. This function will scan the bus for us, using the
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information as defined in the lists explained above. If a device is
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detected at a specific address, another callback is called.
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int foo_attach_adapter(struct i2c_adapter *adapter)
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{
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return i2c_probe(adapter,&addr_data,&foo_detect_client);
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}
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Remember, structure `addr_data' is defined by the macros explained above,
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so you do not have to define it yourself.
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2005-07-31 21:42:02 +02:00
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The i2c_probe function will call the foo_detect_client
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2005-04-17 00:20:36 +02:00
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function only for those i2c addresses that actually have a device on
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them (unless a `force' parameter was used). In addition, addresses that
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are already in use (by some other registered client) are skipped.
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2007-05-01 23:26:31 +02:00
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The detect client function (Legacy model)
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-----------------------------------------
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2005-04-17 00:20:36 +02:00
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2005-07-31 21:42:02 +02:00
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The detect client function is called by i2c_probe. The `kind' parameter
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contains -1 for a probed detection, 0 for a forced detection, or a positive
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number for a forced detection with a chip type forced.
|
2005-04-17 00:20:36 +02:00
|
|
|
|
[PATCH] I2C: Rewrite i2c_probe
i2c_probe was quite complex and slow, so I rewrote it in a more
efficient and hopefully clearer way.
Note that this slightly changes the way the module parameters are
handled. This shouldn't change anything for the most common cases
though.
For one thing, the function now respects the order of the parameters
for address probing. It used to always do lower addresses first. The
new approach gives the user more control.
For another, ignore addresses don't overrule probe addresses anymore.
This could have been restored the way it was at the cost of a few more
lines of code, but I don't think it's worth it. Both lists are given
as module parameters, so a user would be quite silly to specify the
same addresses in both lists. The normal addresses list is the only
one that isn't controlled by a module parameter, thus is the only one
the user may reasonably want to remove an address from.
Another significant change is the fact that i2c_probe() will no more
stop when a detection function returns -ENODEV. Just because a driver
found a chip it doesn't support isn't a valid reason to stop all
probings for this one driver. This closes the long standing lm_sensors
ticket #1807.
http://www2.lm-sensors.nu/~lm78/readticket.cgi?ticket=1807
I updated the documentation accordingly.
In terms of algorithmic complexity, the new code is way better. If
I is the ignore address count, P the probe address count, N the
normal address count and F the force address count, the old code
was doing 128 * (F + I + P + N) iterations max, while the new code
does F + P + ((I+1) * N) iterations max. For the most common case
where F, I and P are empty, this is down from 128 * N to N.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2005-08-09 20:17:55 +02:00
|
|
|
Returning an error different from -ENODEV in a detect function will cause
|
|
|
|
the detection to stop: other addresses and adapters won't be scanned.
|
|
|
|
This should only be done on fatal or internal errors, such as a memory
|
|
|
|
shortage or i2c_attach_client failing.
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
For now, you can ignore the `flags' parameter. It is there for future use.
|
|
|
|
|
|
|
|
int foo_detect_client(struct i2c_adapter *adapter, int address,
|
2007-05-01 23:26:35 +02:00
|
|
|
int kind)
|
2005-04-17 00:20:36 +02:00
|
|
|
{
|
|
|
|
int err = 0;
|
|
|
|
int i;
|
2007-05-01 23:26:35 +02:00
|
|
|
struct i2c_client *client;
|
2005-04-17 00:20:36 +02:00
|
|
|
struct foo_data *data;
|
2007-05-01 23:26:35 +02:00
|
|
|
const char *name = "";
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
/* Let's see whether this adapter can support what we need.
|
2007-05-01 23:26:35 +02:00
|
|
|
Please substitute the things you need here! */
|
2005-04-17 00:20:36 +02:00
|
|
|
if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
|
|
|
|
I2C_FUNC_SMBUS_WRITE_BYTE))
|
|
|
|
goto ERROR0;
|
|
|
|
|
|
|
|
/* OK. For now, we presume we have a valid client. We now create the
|
|
|
|
client structure, even though we cannot fill it completely yet.
|
|
|
|
But it allows us to access several i2c functions safely */
|
|
|
|
|
2005-10-17 23:16:25 +02:00
|
|
|
if (!(data = kzalloc(sizeof(struct foo_data), GFP_KERNEL))) {
|
2005-04-17 00:20:36 +02:00
|
|
|
err = -ENOMEM;
|
|
|
|
goto ERROR0;
|
|
|
|
}
|
|
|
|
|
2007-05-01 23:26:35 +02:00
|
|
|
client = &data->client;
|
|
|
|
i2c_set_clientdata(client, data);
|
2005-04-17 00:20:36 +02:00
|
|
|
|
2007-05-01 23:26:35 +02:00
|
|
|
client->addr = address;
|
|
|
|
client->adapter = adapter;
|
|
|
|
client->driver = &foo_driver;
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
/* Now, we do the remaining detection. If no `force' parameter is used. */
|
|
|
|
|
|
|
|
/* First, the generic detection (if any), that is skipped if any force
|
|
|
|
parameter was used. */
|
|
|
|
if (kind < 0) {
|
|
|
|
/* The below is of course bogus */
|
2007-05-01 23:26:35 +02:00
|
|
|
if (foo_read(client, FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
|
2005-04-17 00:20:36 +02:00
|
|
|
goto ERROR1;
|
|
|
|
}
|
|
|
|
|
|
|
|
/* Next, specific detection. This is especially important for `sensors'
|
|
|
|
devices. */
|
|
|
|
|
|
|
|
/* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
|
|
|
|
was used. */
|
|
|
|
if (kind <= 0) {
|
2007-05-01 23:26:35 +02:00
|
|
|
i = foo_read(client, FOO_REG_CHIPTYPE);
|
2005-04-17 00:20:36 +02:00
|
|
|
if (i == FOO_TYPE_1)
|
|
|
|
kind = chip1; /* As defined in the enum */
|
|
|
|
else if (i == FOO_TYPE_2)
|
|
|
|
kind = chip2;
|
|
|
|
else {
|
|
|
|
printk("foo: Ignoring 'force' parameter for unknown chip at "
|
|
|
|
"adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
|
|
|
|
goto ERROR1;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
/* Now set the type and chip names */
|
|
|
|
if (kind == chip1) {
|
2007-05-01 23:26:35 +02:00
|
|
|
name = "chip1";
|
2005-04-17 00:20:36 +02:00
|
|
|
} else if (kind == chip2) {
|
2007-05-01 23:26:35 +02:00
|
|
|
name = "chip2";
|
2005-04-17 00:20:36 +02:00
|
|
|
}
|
|
|
|
|
|
|
|
/* Fill in the remaining client fields. */
|
2007-05-01 23:26:35 +02:00
|
|
|
strlcpy(client->name, name, I2C_NAME_SIZE);
|
2005-04-17 00:20:36 +02:00
|
|
|
data->type = kind;
|
2007-05-01 23:26:35 +02:00
|
|
|
mutex_init(&data->update_lock); /* Only if you use this field */
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
/* Any other initializations in data must be done here too. */
|
|
|
|
|
|
|
|
/* This function can write default values to the client registers, if
|
|
|
|
needed. */
|
2007-05-01 23:26:35 +02:00
|
|
|
foo_init_client(client);
|
|
|
|
|
|
|
|
/* Tell the i2c layer a new client has arrived */
|
|
|
|
if ((err = i2c_attach_client(client)))
|
|
|
|
goto ERROR1;
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
return 0;
|
|
|
|
|
|
|
|
/* OK, this is not exactly good programming practice, usually. But it is
|
|
|
|
very code-efficient in this case. */
|
|
|
|
|
|
|
|
ERROR1:
|
2005-11-02 21:42:48 +01:00
|
|
|
kfree(data);
|
2005-04-17 00:20:36 +02:00
|
|
|
ERROR0:
|
|
|
|
return err;
|
|
|
|
}
|
|
|
|
|
|
|
|
|
2007-05-01 23:26:31 +02:00
|
|
|
Removing the client (Legacy model)
|
|
|
|
==================================
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
The detach_client call back function is called when a client should be
|
|
|
|
removed. It may actually fail, but only when panicking. This code is
|
|
|
|
much simpler than the attachment code, fortunately!
|
|
|
|
|
|
|
|
int foo_detach_client(struct i2c_client *client)
|
|
|
|
{
|
2007-05-01 23:26:35 +02:00
|
|
|
int err;
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
/* Try to detach the client from i2c space */
|
2005-07-27 22:14:49 +02:00
|
|
|
if ((err = i2c_detach_client(client)))
|
2005-04-17 00:20:36 +02:00
|
|
|
return err;
|
|
|
|
|
2005-11-02 21:42:48 +01:00
|
|
|
kfree(i2c_get_clientdata(client));
|
2005-04-17 00:20:36 +02:00
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
Initializing the module or kernel
|
|
|
|
=================================
|
|
|
|
|
|
|
|
When the kernel is booted, or when your foo driver module is inserted,
|
|
|
|
you have to do some initializing. Fortunately, just attaching (registering)
|
|
|
|
the driver module is usually enough.
|
|
|
|
|
|
|
|
static int __init foo_init(void)
|
|
|
|
{
|
|
|
|
int res;
|
|
|
|
|
|
|
|
if ((res = i2c_add_driver(&foo_driver))) {
|
|
|
|
printk("foo: Driver registration failed, module not inserted.\n");
|
|
|
|
return res;
|
|
|
|
}
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2007-05-01 23:26:35 +02:00
|
|
|
static void __exit foo_cleanup(void)
|
2005-04-17 00:20:36 +02:00
|
|
|
{
|
2007-05-01 23:26:35 +02:00
|
|
|
i2c_del_driver(&foo_driver);
|
2005-04-17 00:20:36 +02:00
|
|
|
}
|
|
|
|
|
|
|
|
/* Substitute your own name and email address */
|
|
|
|
MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
|
|
|
|
MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
|
|
|
|
|
2007-05-01 23:26:35 +02:00
|
|
|
/* a few non-GPL license types are also allowed */
|
|
|
|
MODULE_LICENSE("GPL");
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
module_init(foo_init);
|
|
|
|
module_exit(foo_cleanup);
|
|
|
|
|
|
|
|
Note that some functions are marked by `__init', and some data structures
|
2007-05-01 23:26:35 +02:00
|
|
|
by `__initdata'. These functions and structures can be removed after
|
2005-04-17 00:20:36 +02:00
|
|
|
kernel booting (or module loading) is completed.
|
|
|
|
|
2005-12-18 16:51:55 +01:00
|
|
|
|
2007-02-13 22:09:00 +01:00
|
|
|
Power Management
|
|
|
|
================
|
|
|
|
|
|
|
|
If your I2C device needs special handling when entering a system low
|
|
|
|
power state -- like putting a transceiver into a low power mode, or
|
|
|
|
activating a system wakeup mechanism -- do that in the suspend() method.
|
|
|
|
The resume() method should reverse what the suspend() method does.
|
|
|
|
|
|
|
|
These are standard driver model calls, and they work just like they
|
|
|
|
would for any other driver stack. The calls can sleep, and can use
|
|
|
|
I2C messaging to the device being suspended or resumed (since their
|
|
|
|
parent I2C adapter is active when these calls are issued, and IRQs
|
|
|
|
are still enabled).
|
|
|
|
|
|
|
|
|
|
|
|
System Shutdown
|
|
|
|
===============
|
|
|
|
|
|
|
|
If your I2C device needs special handling when the system shuts down
|
|
|
|
or reboots (including kexec) -- like turning something off -- use a
|
|
|
|
shutdown() method.
|
|
|
|
|
|
|
|
Again, this is a standard driver model call, working just like it
|
|
|
|
would for any other driver stack: the calls can sleep, and can use
|
|
|
|
I2C messaging.
|
|
|
|
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
Command function
|
|
|
|
================
|
|
|
|
|
|
|
|
A generic ioctl-like function call back is supported. You will seldom
|
2005-12-18 16:51:55 +01:00
|
|
|
need this, and its use is deprecated anyway, so newer design should not
|
|
|
|
use it. Set it to NULL.
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
|
|
|
|
Sending and receiving
|
|
|
|
=====================
|
|
|
|
|
|
|
|
If you want to communicate with your device, there are several functions
|
|
|
|
to do this. You can find all of them in i2c.h.
|
|
|
|
|
|
|
|
If you can choose between plain i2c communication and SMBus level
|
|
|
|
communication, please use the last. All adapters understand SMBus level
|
|
|
|
commands, but only some of them understand plain i2c!
|
|
|
|
|
|
|
|
|
|
|
|
Plain i2c communication
|
|
|
|
-----------------------
|
|
|
|
|
|
|
|
extern int i2c_master_send(struct i2c_client *,const char* ,int);
|
|
|
|
extern int i2c_master_recv(struct i2c_client *,char* ,int);
|
|
|
|
|
|
|
|
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
|
|
|
|
parameter contains the bytes the read/write, the third the length of the
|
|
|
|
buffer. Returned is the actual number of bytes read/written.
|
|
|
|
|
|
|
|
extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
|
|
|
|
int num);
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
You can read the file `i2c-protocol' for more information about the
|
|
|
|
actual i2c protocol.
|
|
|
|
|
|
|
|
|
|
|
|
SMBus communication
|
|
|
|
-------------------
|
|
|
|
|
|
|
|
extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
|
|
|
|
unsigned short flags,
|
|
|
|
char read_write, u8 command, int size,
|
|
|
|
union i2c_smbus_data * data);
|
|
|
|
|
|
|
|
This is the generic SMBus function. All functions below are implemented
|
|
|
|
in terms of it. Never use this function directly!
|
|
|
|
|
|
|
|
|
|
|
|
extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
|
|
|
|
extern s32 i2c_smbus_read_byte(struct i2c_client * client);
|
|
|
|
extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
|
|
|
|
extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
|
|
|
|
extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
|
|
|
|
u8 command, u8 value);
|
|
|
|
extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
|
|
|
|
extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
|
|
|
|
u8 command, u16 value);
|
|
|
|
extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
|
|
|
|
u8 command, u8 length,
|
|
|
|
u8 *values);
|
2005-10-08 00:00:31 +02:00
|
|
|
extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
|
|
|
|
u8 command, u8 *values);
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
These ones were removed in Linux 2.6.10 because they had no users, but could
|
|
|
|
be added back later if needed:
|
|
|
|
|
|
|
|
extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
|
|
|
|
u8 command, u8 *values);
|
|
|
|
extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
|
|
|
|
u8 command, u8 length,
|
|
|
|
u8 *values);
|
|
|
|
extern s32 i2c_smbus_process_call(struct i2c_client * client,
|
|
|
|
u8 command, u16 value);
|
|
|
|
extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
|
|
|
|
u8 command, u8 length,
|
|
|
|
u8 *values)
|
|
|
|
|
|
|
|
All these transactions return -1 on failure. The 'write' transactions
|
|
|
|
return 0 on success; the 'read' transactions return the read value, except
|
|
|
|
for read_block, which returns 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
|
|
|
|
actual SMBus protocol.
|
|
|
|
|
|
|
|
|
|
|
|
General purpose routines
|
|
|
|
========================
|
|
|
|
|
|
|
|
Below all general purpose routines are listed, that were not mentioned
|
|
|
|
before.
|
|
|
|
|
2007-05-01 23:26:35 +02:00
|
|
|
/* This call returns a unique low identifier for each registered adapter.
|
2005-04-17 00:20:36 +02:00
|
|
|
*/
|
|
|
|
extern int i2c_adapter_id(struct i2c_adapter *adap);
|
|
|
|
|