Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst
index fbbb283..45953f1 100644
--- a/Documentation/driver-api/dmaengine/client.rst
+++ b/Documentation/driver-api/dmaengine/client.rst
@@ -168,6 +168,13 @@
    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.
+      Consequently, 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