docs: i2c: convert to ReST and add to driver-api bookset

Convert each file at I2C subsystem, renaming them to .rst and
adding to the driver-api book.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/i2c/i2c-stub.rst

@@ -0,0 +1,66 @@
+========
+i2c-stub
+========
+
+Description
+===========
+
+This module is a very simple fake I2C/SMBus driver.  It implements six
+types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w)
+word data, (r/w) I2C block data, and (r/w) SMBus block data.
+
+You need to provide chip addresses as a module parameter when loading this
+driver, which will then only react to SMBus commands to these addresses.
+
+No hardware is needed nor associated with this module.  It will accept write
+quick commands to the specified addresses; it will respond to the other
+commands (also to the specified addresses) by reading from or writing to
+arrays in memory.  It will also spam the kernel logs for every command it
+handles.
+
+A pointer register with auto-increment is implemented for all byte
+operations.  This allows for continuous byte reads like those supported by
+EEPROMs, among others.
+
+SMBus block command support is disabled by default, and must be enabled
+explicitly by setting the respective bits (0x03000000) in the functionality
+module parameter.
+
+SMBus block commands must be written to configure an SMBus command for
+SMBus block operations. Writes can be partial. Block read commands always
+return the number of bytes selected with the largest write so far.
+
+The typical use-case is like this:
+
+	1. load this module
+	2. use i2cset (from the i2c-tools project) to pre-load some data
+	3. load the target chip driver module
+	4. observe its behavior in the kernel log
+
+There's a script named i2c-stub-from-dump in the i2c-tools package which
+can load register values automatically from a chip dump.
+
+Parameters
+==========
+
+int chip_addr[10]:
+	The SMBus addresses to emulate chips at.
+
+unsigned long functionality:
+	Functionality override, to disable some commands. See I2C_FUNC_*
+	constants in <linux/i2c.h> for the suitable values. For example,
+	value 0x1f0000 would only enable the quick, byte and byte data
+	commands.
+
+u8 bank_reg[10], u8 bank_mask[10], u8 bank_start[10], u8 bank_end[10]:
+	Optional bank settings. They tell which bits in which register
+	select the active bank, as well as the range of banked registers.
+
+Caveats
+=======
+
+If your target driver polls some byte or word waiting for it to change, the
+stub could lock it up.  Use i2cset to unlock it.
+
+If you spam it hard enough, printk can be lossy.  This module really wants
+something like relayfs.