Patch "dmaengine: pl330: Really fix choppy sound because of wrong residue calculation" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

dmaengine: pl330: Really fix choppy sound because of wrong residue calculation

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
dmaengine-pl330-really-fix-choppy-sound-because-of-wrong-residue-calculation.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Krzysztof Kozlowski <[email protected]>
Date: Mon, 15 Jun 2015 23:00:09 +0900
Subject: dmaengine: pl330: Really fix choppy sound because of wrong residue calculation

From: Krzysztof Kozlowski <[email protected]>

commit 5dd90e5b91e0f5c925b12b132c7cd27538870256 upstream.

When pl330 driver was used during sound playback, after some time or after a number of plays the sound became choppy or totally noisy. For example on Odroid XU3 board the first four executions of aplay with small WAVE worked fine, but fifth was unrecognizable with errors:

	$ aplay /usr/share/sounds/alsa/Front_Right.wava
	underrun!!! (at least 0.095 ms long)

Issue was caused by wrong residue reported by pl330 driver to pcm_dmaengine for its cyclic dma transfers.

The pl330_tx_status(), residue reporting function, used a "last" flag in a descriptor to indicate that there is no more data to send.

The pl330_tx_submit() iterated over descriptors trying to remove this flag from them and then mark last descriptor as "last". However when iterating it actually removed the flag not from descriptors but always from last of it (and then reset it). Thus effectively once some descriptor was marked as last, then it stayed like this forever causing residue to be reported too low.

---
 drivers/dma/pl330.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -2328,7 +2328,7 @@ static dma_cookie_t pl330_tx_submit(stru
 			desc->txd.callback = last->txd.callback;
 			desc->txd.callback_param = last->txd.callback_param;
 		}
-		last->last = false;
+		desc->last = false;
 
 		dma_cookie_assign(&desc->txd);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/dmaengine-pl330-really-fix-choppy-sound-because-of-wrong-residue-calculation.patch