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+				DMA Test Guide
+				==============
+
+		Andy Shevchenko <andriy.shevchenko@linux.intel.com>
+
+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
+
+...or:
+	% 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.channel=dma0chan0 dmatest.timeout=2000 dmatest.iterations=1 dmatest.run=1
+
+Hint: available channel list could be extracted by running the following
+command:
+	% 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
+stops.
+
+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.
+
+Example:
+	% modprobe dmatest run=1 iterations=42 wait=1
+	% modprobe -r dmatest
+...or:
+	% 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.
+
+Example:
+	% 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.