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DMA Test Guide
Andy Shevchenko <>
This small document introduces how to test DMA drivers using dmatest module.
Part 1 - How to build the test module
The menuconfig contains an option that could be found by following path:
Device Drivers -> DMA Engine support -> DMA Test client
In the configuration file the option called CONFIG_DMATEST. The dmatest could
be built as module or inside kernel. Let's consider those cases.
Part 2 - When dmatest is built as a module...
Example of usage:
% modprobe dmatest channel=dma0chan0 timeout=2000 iterations=1 run=1
% modprobe dmatest
% echo dma0chan0 > /sys/module/dmatest/parameters/channel
% echo 2000 > /sys/module/dmatest/parameters/timeout
% echo 1 > /sys/module/dmatest/parameters/iterations
% echo 1 > /sys/module/dmatest/parameters/run
...or on the kernel command line: dmatest.timeout=2000 dmatest.iterations=1
Hint: available channel list could be extracted by running the following
% ls -1 /sys/class/dma/
Once started a message like "dmatest: Started 1 threads using dma0chan0" is
emitted. After that only test failure messages are reported until the test
Note that running a new test will not stop any in progress test.
The following command returns the state of the test.
% cat /sys/module/dmatest/parameters/run
To wait for test completion userpace can poll 'run' until it is false, or use
the wait parameter. Specifying 'wait=1' when loading the module causes module
initialization to pause until a test run has completed, while reading
/sys/module/dmatest/parameters/wait waits for any running test to complete
before returning. For example, the following scripts wait for 42 tests
to complete before exiting. Note that if 'iterations' is set to 'infinite' then
waiting is disabled.
% modprobe dmatest run=1 iterations=42 wait=1
% modprobe -r dmatest
% modprobe dmatest run=1 iterations=42
% cat /sys/module/dmatest/parameters/wait
% modprobe -r dmatest
Part 3 - When built-in in the kernel...
The module parameters that is supplied to the kernel command line will be used
for the first performed test. After user gets a control, the test could be
re-run with the same or different parameters. For the details see the above
section "Part 2 - When dmatest is built as a module..."
In both cases the module parameters are used as the actual values for the test
case. You always could check them at run-time by running
% grep -H . /sys/module/dmatest/parameters/*
Part 4 - Gathering the test results
Test results are printed to the kernel log buffer with the format:
"dmatest: result <channel>: <test id>: '<error msg>' with src_off=<val> dst_off=<val> len=<val> (<err code>)"
Example of output:
% dmesg | tail -n 1
dmatest: result dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)
The message format is unified across the different types of errors. A number in
the parens represents additional information, e.g. error code, error counter,
or status. A test thread also emits a summary line at completion listing the
number of tests executed, number that failed, and a result code.
% dmesg | tail -n 1
dmatest: dma0chan0-copy0: summary 1 test, 0 failures 1000 iops 100000 KB/s (0)
The details of a data miscompare error are also emitted, but do not follow the
above format.