mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-18 17:54:13 +08:00
ccf988b66d
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>
67 lines
2.3 KiB
ReStructuredText
67 lines
2.3 KiB
ReStructuredText
========
|
|
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.
|