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[PATCH] doc:dmaengine: clarify DMA desc. pointer after submission

It clarifies that the DMA description pointer returned by
`dmaengine_prep_*` function should not be used after submission.

Signed-off-by: Federico Vaga <federico.vaga@xxxxxxx>
 Documentation/driver-api/dmaengine/client.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst
index fbbb2831f29f..d728e50105eb 100644
--- a/Documentation/driver-api/dmaengine/client.rst
+++ b/Documentation/driver-api/dmaengine/client.rst
@@ -168,6 +168,13 @@ The details of these operations are:
    dmaengine_submit() will not start the DMA operation, it merely adds
    it to the pending queue. For this, see step 5, dma_async_issue_pending.
+   .. note::
+      After calling ``dmaengine_submit()`` the submitted transfer descriptor
+      (``struct dma_async_tx_descriptor``) belongs to the DMA engine.
+      Consequentially, the client must consider invalid the pointer to that
+      descriptor.
 5. Issue pending DMA requests and wait for callback notification
    The transactions in the pending queue can be activated by calling the