linux-kernel - Re: [PATCH] dmaengine: pl330: Really fix choppy sound because of wrong residue calculation

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Date:	Tue, 7 Jul 2015 09:30:50 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Krzysztof Kozlowski <k.kozlowski.k@...il.com>
Cc:	Dan Williams <dan.j.williams@...el.com>, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org, gabriel@...een.is,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH] dmaengine: pl330: Really fix choppy sound because of
 wrong residue calculation

On Mon, Jun 15, 2015 at 11:00:09PM +0900, Krzysztof Kozlowski wrote:
> 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.

Applied, thanks

-- 
~Vinod

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