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Subject[PATCH] Documentation: dmaengine: clean up description of dmatest usage
Fix the formatting of the multi-channel test usage example. Call out
the note about parameter ordering and add detail on the settings of
parameters for the new version of dmatest.

Fixes: f80f9988a26d7 ("dmaengine: Documentation: Add documentation for multi chan testing")

Signed-off-by: Gary R Hook <>
Documentation/driver-api/dmaengine/dmatest.rst | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/Documentation/driver-api/dmaengine/dmatest.rst b/Documentation/driver-api/dmaengine/dmatest.rst
index e78d070bb468..ee268d445d38 100644
--- a/Documentation/driver-api/dmaengine/dmatest.rst
+++ b/Documentation/driver-api/dmaengine/dmatest.rst
@@ -44,7 +44,8 @@ Example of usage::

dmatest.timeout=2000 dmatest.iterations=1

-Example of multi-channel test usage:
+Example of multi-channel test usage (new in the 5.0 kernel)::
% modprobe dmatest
% echo 2000 > /sys/module/dmatest/parameters/timeout
% echo 1 > /sys/module/dmatest/parameters/iterations
@@ -53,15 +54,18 @@ Example of multi-channel test usage:
% 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.
+.. note::
+ For all tests, starting in the 5.0 kernel, either single- or multi-channel,
+ the channel parameter(s) must be set after all other parameters. It is at
+ that time that the existing parameter values are acquired for use by the
+ thread(s). All other parameters are shared. Therefore, if changes are made
+ to any of the other parameters, and an additional channel specified, the
+ (shared) parameters used for all threads will use the new values.
+ After the channels are specified, each thread is set as pending. All threads
+ begin execution when the run parameter is set to 1.

.. hint::
- available channel list could be extracted by running the following command::
+ A list of available channels can be found by running the following command::

% ls -1 /sys/class/dma/

@@ -204,6 +208,7 @@ Releasing Channels
Channels can be freed by setting run to 0.

% echo dma0chan1 > /sys/module/dmatest/parameters/channel
dmatest: Added 1 threads using dma0chan1
% cat /sys/class/dma/dma0chan1/in_use
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