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Devices offering SMBus block process calls are rare, so add it to the testunit. This is also a good test case for testing proper I2C_M_RECV_LEN flag handling of I2C bus masters emulating SMBus. Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com> Signed-off-by: Wolfram Sang <wsa@kernel.org>
89 lines
3.8 KiB
ReStructuredText
89 lines
3.8 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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================================
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Linux I2C slave testunit backend
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================================
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by Wolfram Sang <wsa@sang-engineering.com> in 2020
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This backend can be used to trigger test cases for I2C bus masters which
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require a remote device with certain capabilities (and which are usually not so
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easy to obtain). Examples include multi-master testing, and SMBus Host Notify
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testing. For some tests, the I2C slave controller must be able to switch
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between master and slave mode because it needs to send data, too.
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Note that this is a device for testing and debugging. It should not be enabled
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in a production build. And while there is some versioning and we try hard to
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keep backward compatibility, there is no stable ABI guaranteed!
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Instantiating the device is regular. Example for bus 0, address 0x30:
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# echo "slave-testunit 0x1030" > /sys/bus/i2c/devices/i2c-0/new_device
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After that, you will have a write-only device listening. Reads will just return
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an 8-bit version number of the testunit. When writing, the device consists of 4
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8-bit registers and, except for some "partial" commands, all registers must be
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written to start a testcase, i.e. you usually write 4 bytes to the device. The
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registers are:
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0x00 CMD - which test to trigger
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0x01 DATAL - configuration byte 1 for the test
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0x02 DATAH - configuration byte 2 for the test
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0x03 DELAY - delay in n * 10ms until test is started
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Using 'i2cset' from the i2c-tools package, the generic command looks like:
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# i2cset -y <bus_num> <testunit_address> <CMD> <DATAL> <DATAH> <DELAY> i
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DELAY is a generic parameter which will delay the execution of the test in CMD.
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While a command is running (including the delay), new commands will not be
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acknowledged. You need to wait until the old one is completed.
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The commands are described in the following section. An invalid command will
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result in the transfer not being acknowledged.
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Commands
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--------
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0x00 NOOP (reserved for future use)
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0x01 READ_BYTES (also needs master mode)
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DATAL - address to read data from (lower 7 bits, highest bit currently unused)
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DATAH - number of bytes to read
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This is useful to test if your bus master driver is handling multi-master
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correctly. You can trigger the testunit to read bytes from another device on
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the bus. If the bus master under test also wants to access the bus at the same
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time, the bus will be busy. Example to read 128 bytes from device 0x50 after
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50ms of delay:
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# i2cset -y 0 0x30 0x01 0x50 0x80 0x05 i
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0x02 SMBUS_HOST_NOTIFY (also needs master mode)
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DATAL - low byte of the status word to send
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DATAH - high byte of the status word to send
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This test will send an SMBUS_HOST_NOTIFY message to the host. Note that the
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status word is currently ignored in the Linux Kernel. Example to send a
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notification after 10ms:
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# i2cset -y 0 0x30 0x02 0x42 0x64 0x01 i
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0x03 SMBUS_BLOCK_PROC_CALL (partial command)
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DATAL - must be '1', i.e. one further byte will be written
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DATAH - number of bytes to be sent back
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DELAY - not applicable, partial command!
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This test will respond to a block process call as defined by the SMBus
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specification. The one data byte written specifies how many bytes will be sent
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back in the following read transfer. Note that in this read transfer, the
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testunit will prefix the length of the bytes to follow. So, if your host bus
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driver emulates SMBus calls like the majority does, it needs to support the
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I2C_M_RECV_LEN flag of an i2c_msg. This is a good testcase for it. The returned
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data consists of the length first, and then of an array of bytes from length-1
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to 0. Here is an example which emulates i2c_smbus_block_process_call() using
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i2ctransfer (you need i2c-tools v4.2 or later):
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# i2ctransfer -y 0 w3@0x30 0x03 0x01 0x10 r?
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0x10 0x0f 0x0e 0x0d 0x0c 0x0b 0x0a 0x09 0x08 0x07 0x06 0x05 0x04 0x03 0x02 0x01 0x00
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