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author | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-07-26 09:51:16 -0300 |
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committer | Jonathan Corbet <corbet@lwn.net> | 2019-07-31 13:25:27 -0600 |
commit | ccf988b66d697efcd0ceccc2398e0d9b909cd17c (patch) | |
tree | 94022b812a20419675e4cac5af1540d75523d31d /Documentation/i2c/i2c-stub.rst | |
parent | 09f4c750a8c7d1fc0b7bb3a7aa1de55de897a375 (diff) | |
download | linux-ccf988b66d697efcd0ceccc2398e0d9b909cd17c.tar.gz linux-ccf988b66d697efcd0ceccc2398e0d9b909cd17c.tar.bz2 linux-ccf988b66d697efcd0ceccc2398e0d9b909cd17c.zip |
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>
Diffstat (limited to 'Documentation/i2c/i2c-stub.rst')
-rw-r--r-- | Documentation/i2c/i2c-stub.rst | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/Documentation/i2c/i2c-stub.rst b/Documentation/i2c/i2c-stub.rst new file mode 100644 index 000000000000..a6fc6916d6bc --- /dev/null +++ b/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. |