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diff --git a/Documentation/i2c/slave-testunit-backend.rst b/Documentation/i2c/slave-testunit-backend.rst new file mode 100644 index 000000000000..2c38e64f0bac --- /dev/null +++ b/Documentation/i2c/slave-testunit-backend.rst @@ -0,0 +1,69 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================ +Linux I2C slave testunit backend +================================ + +by Wolfram Sang <wsa@sang-engineering.com> in 2020 + +This backend can be used to trigger test cases for I2C bus masters which +require a remote device with certain capabilities (and which are usually not so +easy to obtain). Examples include multi-master testing, and SMBus Host Notify +testing. For some tests, the I2C slave controller must be able to switch +between master and slave mode because it needs to send data, too. + +Note that this is a device for testing and debugging. It should not be enabled +in a production build. And while there is some versioning and we try hard to +keep backward compatibility, there is no stable ABI guaranteed! + +Instantiating the device is regular. Example for bus 0, address 0x30: + +# echo "slave-testunit 0x1030" > /sys/bus/i2c/devices/i2c-0/new_device + +After that, you will have a write-only device listening. Reads will just return +an 8-bit version number of the testunit. When writing, the device consists of 4 +8-bit registers and all must be written to start a testcase, i.e. you must +always write 4 bytes to the device. The registers are: + +0x00 CMD - which test to trigger +0x01 DATAL - configuration byte 1 for the test +0x02 DATAH - configuration byte 2 for the test +0x03 DELAY - delay in n * 10ms until test is started + +Using 'i2cset' from the i2c-tools package, the generic command looks like: + +# i2cset -y <bus_num> <testunit_address> <CMD> <DATAL> <DATAH> <DELAY> i + +DELAY is a generic parameter which will delay the execution of the test in CMD. +While a command is running (including the delay), new commands will not be +acknowledged. You need to wait until the old one is completed. + +The commands are described in the following section. An invalid command will +result in the transfer not being acknowledged. + +Commands +-------- + +0x00 NOOP (reserved for future use) + +0x01 READ_BYTES (also needs master mode) + DATAL - address to read data from (lower 7 bits, highest bit currently unused) + DATAH - number of bytes to read + +This is useful to test if your bus master driver is handling multi-master +correctly. You can trigger the testunit to read bytes from another device on +the bus. If the bus master under test also wants to access the bus at the same +time, the bus will be busy. Example to read 128 bytes from device 0x50 after +50ms of delay: + +# i2cset -y 0 0x30 0x01 0x50 0x80 0x05 i + +0x02 SMBUS_HOST_NOTIFY (also needs master mode) + DATAL - low byte of the status word to send + DATAH - high byte of the status word to send + +This test will send an SMBUS_HOST_NOTIFY message to the host. Note that the +status word is currently ignored in the Linux Kernel. Example to send a +notification after 10ms: + +# i2cset -y 0 0x30 0x02 0x42 0x64 0x01 i |