dmaengine: Documentation: Add documentation for multi chan testing

Modify documentation to add multi channel testing support.
Signed-off-by: Seraj Alijan <seraj.alijan@sondrel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/driver-api/dmaengine/dmatest.rst

@@ -26,28 +26,43 @@ Part 2 - When dmatest is built as a module
 
 Example of usage::
 
-    % modprobe dmatest channel=dma0chan0 timeout=2000 iterations=1 run=1
+    % modprobe dmatest timeout=2000 iterations=1 channel=dma0chan0 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 dma0chan0 > /sys/module/dmatest/parameters/channel
     % 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
+    dmatest.timeout=2000 dmatest.iterations=1 dmatest.channel=dma0chan0 dmatest.run=1
+
+Example of multi-channel test usage:
+    % modprobe dmatest
+    % echo 2000 > /sys/module/dmatest/parameters/timeout
+    % echo 1 > /sys/module/dmatest/parameters/iterations
+    % echo dma0chan0 > /sys/module/dmatest/parameters/channel
+    % echo dma0chan1 > /sys/module/dmatest/parameters/channel
+    % echo dma0chan2 > /sys/module/dmatest/parameters/channel
+    % echo 1 > /sys/module/dmatest/parameters/run
 
+Note: the channel parameter should always be the last parameter set prior to
+running the test (setting run=1), this is because upon setting the channel
+parameter, that specific channel is requested using the dmaengine and a thread
+is created with the existing parameters. This thread is set as pending
+and will be executed once run is set to 1. Any parameters set after the thread
+is created are not applied.
 .. 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.
+Once started a message like " dmatest: Added 1 threads using dma0chan0" is
+emitted. A thread for that specific channel is created and is now pending, the
+pending thread is started once run is to 1.
 
 Note that running a new test will not stop any in progress test.
 
@@ -112,3 +127,85 @@ Example::
 
 The details of a data miscompare error are also emitted, but do not follow the
 above format.
+
+Part 5 - Handling channel allocation
+====================================
+
+Allocating Channels
+-------------------
+
+Channels are required to be configured prior to starting the test run.
+Attempting to run the test without configuring the channels will fail.
+
+Example::
+
+    % echo 1 > /sys/module/dmatest/parameters/run
+    dmatest: Could not start test, no channels configured
+
+Channels are registered using the "channel" parameter. Channels can be requested by their
+name, once requested, the channel is registered and a pending thread is added to the test list.
+
+Example::
+
+    % echo dma0chan2 > /sys/module/dmatest/parameters/channel
+    dmatest: Added 1 threads using dma0chan2
+
+More channels can be added by repeating the example above.
+Reading back the channel parameter will return the name of last channel that was added successfully.
+
+Example::
+
+    % echo dma0chan1 > /sys/module/dmatest/parameters/channel
+    dmatest: Added 1 threads using dma0chan1
+    % echo dma0chan2 > /sys/module/dmatest/parameters/channel
+    dmatest: Added 1 threads using dma0chan2
+    % cat /sys/module/dmatest/parameters/channel
+    dma0chan2
+
+Another method of requesting channels is to request a channel with an empty string, Doing so
+will request all channels available to be tested:
+
+Example::
+
+    % echo "" > /sys/module/dmatest/parameters/channel
+    dmatest: Added 1 threads using dma0chan0
+    dmatest: Added 1 threads using dma0chan3
+    dmatest: Added 1 threads using dma0chan4
+    dmatest: Added 1 threads using dma0chan5
+    dmatest: Added 1 threads using dma0chan6
+    dmatest: Added 1 threads using dma0chan7
+    dmatest: Added 1 threads using dma0chan8
+
+At any point during the test configuration, reading the "test_list" parameter will
+print the list of currently pending tests.
+
+Example::
+
+    % cat /sys/module/dmatest/parameters/test_list
+    dmatest: 1 threads using dma0chan0
+    dmatest: 1 threads using dma0chan3
+    dmatest: 1 threads using dma0chan4
+    dmatest: 1 threads using dma0chan5
+    dmatest: 1 threads using dma0chan6
+    dmatest: 1 threads using dma0chan7
+    dmatest: 1 threads using dma0chan8
+
+Note: Channels will have to be configured for each test run as channel configurations do not
+carry across to the next test run.
+
+Releasing Channels
+-------------------
+
+Channels can be freed by setting run to 0.
+
+Example::
+    % echo dma0chan1 > /sys/module/dmatest/parameters/channel
+    dmatest: Added 1 threads using dma0chan1
+    % cat /sys/class/dma/dma0chan1/in_use
+    1
+    % echo 0 > /sys/module/dmatest/parameters/run
+    % cat /sys/class/dma/dma0chan1/in_use
+    0
+
+Channels allocated by previous test runs are automatically freed when a new
+channel is requested after completing a successful test run.