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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...
After mounting debugfs and loading the module, the /sys/kernel/debug/dmatest
folder with nodes will be created. They are the same as module parameters with
addition of the 'run' node that controls run and stop phases of the test.
Note that in this case test will not run on load automatically.
Example of usage:
% echo dma0chan0 > /sys/kernel/debug/dmatest/channel
% echo 2000 > /sys/kernel/debug/dmatest/timeout
% echo 1 > /sys/kernel/debug/dmatest/iterations
% echo 1 > /sys/kernel/debug/dmatest/run
Hint: available channel list could be extracted by running the following
% ls -1 /sys/class/dma/
After a while you will start to get messages about current status or error like
in the original code.
Note that running a new test will not stop any in progress test.
The following command should return actual state of the test.
% cat /sys/kernel/debug/dmatest/run
To wait for test done the user may perform a busy loop that checks the state.
% while [ $(cat /sys/kernel/debug/dmatest/run) = "Y" ]
> do
> echo -n "."
> sleep 1
> done
> echo
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 initial 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
The module provides a storage for the test results in the memory. The gathered
data could be used after test is done.
The special file 'results' in the debugfs represents gathered data of the in
progress test. The messages collected are printed to the kernel log as well.
Example of output:
% cat /sys/kernel/debug/dmatest/results
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.
Comparison between buffers is stored to the dedicated structure.
Note that the verify result is now accessible only via file 'results' in the