i2c: Add kernel documentation

Generate I2C kerneldoc; fix various glitches and add "context" sections to
that documentation.  Most I2C and SMBus functions still have no kerneldoc.

Let me suggest providing kerneldoc for all the i2c_smbus_*() functions as
a small and mostly self-contained project for anyone so inclined.  :)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

Documentation/DocBook/kernel-api.tmpl

@@ -643,6 +643,60 @@ X!Idrivers/video/console/fonts.c
 !Edrivers/spi/spi.c
   </chapter>
 
+  <chapter id="i2c">
+     <title>I<superscript>2</superscript>C and SMBus Subsystem</title>
+
+     <para>
+	I<superscript>2</superscript>C (or without fancy typography, "I2C")
+	is an acronym for the "Inter-IC" bus, a simple bus protocol which is
+	widely used where low data rate communications suffice.
+	Since it's also a licensed trademark, some vendors use another
+	name (such as "Two-Wire Interface", TWI) for the same bus.
+	I2C only needs two signals (SCL for clock, SDA for data), conserving
+	board real estate and minimizing signal quality issues.
+	Most I2C devices use seven bit addresses, and bus speeds of up
+	to 400 kHz; there's a high speed extension (3.4 MHz) that's not yet
+	found wide use.
+	I2C is a multi-master bus; open drain signaling is used to
+	arbitrate between masters, as well as to handshake and to
+	synchronize clocks from slower clients.
+     </para>
+
+     <para>
+	The Linux I2C programming interfaces support only the master
+	side of bus interactions, not the slave side.
+	The programming interface is structured around two kinds of driver,
+	and two kinds of device.
+	An I2C "Adapter Driver" abstracts the controller hardware; it binds
+	to a physical device (perhaps a PCI device or platform_device) and
+	exposes a <structname>struct i2c_adapter</structname> representing
+	each I2C bus segment it manages.
+	On each I2C bus segment will be I2C devices represented by a
+	<structname>struct i2c_client</structname>.  Those devices will
+	be bound to a <structname>struct i2c_driver</structname>,
+	which should follow the standard Linux driver model.
+	(At this writing, a legacy model is more widely used.)
+	There are functions to perform various I2C protocol operations; at
+	this writing all such functions are usable only from task context.
+     </para>
+
+     <para>
+	The System Management Bus (SMBus) is a sibling protocol.  Most SMBus
+	systems are also I2C conformant.  The electrical constraints are
+	tighter for SMBus, and it standardizes particular protocol messages
+	and idioms.  Controllers that support I2C can also support most
+	SMBus operations, but SMBus controllers don't support all the protocol
+	options that an I2C controller will.
+	There are functions to perform various SMBus protocol operations,
+	either using I2C primitives or by issuing SMBus commands to
+	i2c_adapter devices which don't support those I2C operations.
+     </para>
+
+!Iinclude/linux/i2c.h
+!Fdrivers/i2c/i2c-boardinfo.c i2c_register_board_info
+!Edrivers/i2c/i2c-core.c
+  </chapter>
+
   <chapter id="splice">
       <title>splice API</title>
   <para>)
@@ -654,4 +708,5 @@ X!Idrivers/video/console/fonts.c
 !Ffs/splice.c
   </chapter>
 
+
 </book>

drivers/i2c/i2c-core.c

@@ -207,6 +207,7 @@ EXPORT_SYMBOL_GPL(i2c_bus_type);
  * i2c_new_device - instantiate an i2c device for use with a new style driver
  * @adap: the adapter managing the device
  * @info: describes one I2C device; bus_num is ignored
+ * Context: can sleep
  *
  * Create a device to work with a new style i2c driver, where binding is
  * handled through driver model probe()/remove() methods.  This call is not
@@ -255,6 +256,7 @@ EXPORT_SYMBOL_GPL(i2c_new_device);
 /**
  * i2c_unregister_device - reverse effect of i2c_new_device()
  * @client: value returned from i2c_new_device()
+ * Context: can sleep
  */
 void i2c_unregister_device(struct i2c_client *client)
 {
@@ -379,6 +381,7 @@ out_list:
 /**
  * i2c_add_adapter - declare i2c adapter, use dynamic bus number
  * @adapter: the adapter to add
+ * Context: can sleep
  *
  * This routine is used to declare an I2C adapter when its bus number
  * doesn't matter.  Examples: for I2C adapters dynamically added by
@@ -416,6 +419,7 @@ EXPORT_SYMBOL(i2c_add_adapter);
 /**
  * i2c_add_numbered_adapter - declare i2c adapter, use static bus number
  * @adap: the adapter to register (with adap->nr initialized)
+ * Context: can sleep
  *
  * This routine is used to declare an I2C adapter when its bus number
  * matters.  Example: for I2C adapters from system-on-chip CPUs, or
@@ -463,6 +467,14 @@ retry:
 }
 EXPORT_SYMBOL_GPL(i2c_add_numbered_adapter);
 
+/**
+ * i2c_del_adapter - unregister I2C adapter
+ * @adap: the adapter being unregistered
+ * Context: can sleep
+ *
+ * This unregisters an I2C adapter which was previously registered
+ * by @i2c_add_adapter or @i2c_add_numbered_adapter.
+ */
 int i2c_del_adapter(struct i2c_adapter *adap)
 {
 	struct list_head  *item, *_n;
@@ -598,6 +610,7 @@ EXPORT_SYMBOL(i2c_register_driver);
 /**
  * i2c_del_driver - unregister I2C driver
  * @driver: the driver being unregistered
+ * Context: can sleep
  */
 void i2c_del_driver(struct i2c_driver *driver)
 {

include/linux/i2c.h

@@ -150,15 +150,20 @@ struct i2c_driver {
 
 /**
  * struct i2c_client - represent an I2C slave device
+ * @flags: I2C_CLIENT_TEN indicates the device uses a ten bit chip address;
+ *	I2C_CLIENT_PEC indicates it uses SMBus Packet Error Checking
  * @addr: Address used on the I2C bus connected to the parent adapter.
  * @name: Indicates the type of the device, usually a chip name that's
  *	generic enough to hide second-sourcing and compatible revisions.
+ * @adapter: manages the bus segment hosting this I2C device
  * @dev: Driver model device node for the slave.
+ * @irq: indicates the IRQ generated by this device (if any)
  * @driver_name: Identifies new-style driver used with this device; also
  *	used as the module name for hotplug/coldplug modprobe support.
  *
  * An i2c_client identifies a single device (i.e. chip) connected to an
- * i2c bus. The behaviour is defined by the routines of the driver.
+ * i2c bus. The behaviour exposed to Linux is defined by the driver
+ * managing the device.
  */
 struct i2c_client {
 	unsigned short flags;		/* div., see below		*/
@@ -201,7 +206,7 @@ static inline void i2c_set_clientdata (struct i2c_client *dev, void *data)
  * @addr: stored in i2c_client.addr
  * @platform_data: stored in i2c_client.dev.platform_data
  * @irq: stored in i2c_client.irq
-
+ *
  * I2C doesn't actually support hardware probing, although controllers and
  * devices may be able to use I2C_SMBUS_QUICK to tell whether or not there's
  * a device at a given address.  Drivers commonly need more information than
@@ -210,7 +215,7 @@ static inline void i2c_set_clientdata (struct i2c_client *dev, void *data)
  * i2c_board_info is used to build tables of information listing I2C devices
  * that are present.  This information is used to grow the driver model tree
  * for "new style" I2C drivers.  For mainboards this is done statically using
- * i2c_register_board_info(), where @bus_num represents an adapter that isn't
+ * i2c_register_board_info(); bus numbers identify adapters that aren't
  * yet available.  For add-on boards, i2c_new_device() does this dynamically
  * with the adapter already known.
  */