linux-kernel - Re: [alsa-devel] [PATCH v2 2/3] ASoC: dmaengine-pcm: Rename and deprecate snd_dmaengine_pcm

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Date:	Wed, 20 Jun 2012 21:41:32 +0800
From:	Dong Aisheng <aisheng.dong@...escale.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
CC:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>, Vinod Koul <vinod.koul@...el.com>,
	Ola Lilja <ola.o.lilja@...ricsson.com>,
	<alsa-devel@...a-project.org>,
	Russell King <linux@....linux.org.uk>,
	Mika Westerberg <mika.westerberg@....fi>,
	<linux-kernel@...r.kernel.org>, Shawn Guo <shawn.guo@...aro.org>
Subject: Re: [alsa-devel] [PATCH v2 2/3] ASoC: dmaengine-pcm: Rename and
 deprecate snd_dmaengine_pcm_pointer

On Mon, Jun 11, 2012 at 08:11:41PM +0200, Lars-Peter Clausen wrote:
> Currently the sound dmaengine pcm helper functions implement the pcm_pointer
> callback by trying to count the number of elapsed periods. This is done by
> advancing the stream position in the dmaengine callback by one period.
> Unfortunately there is no guarantee that the callback will be called for each
> elapsed period. It may be possible that under high system load it is only called
> once for multiple elapsed periods. This patch renames the current implementation
> and documents its shortcomings and that it should not be used anymore in new
> drivers.
> 
> The next patch will introduce a new snd_dmaengine_pcm_pointer which will be
> implemented based on querying the current stream position from the dma device.
> 
> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> 
Acked-by: Dong Aisheng <dong.aisheng@...aro.org>

> ---
> If you are maintaining a pcm driver which use the dmaengine pcm helper please
> check if you platform works with the new snd_dmaengine_pcm_pointer
> implementation which is added in the next patch (ux500 seems to be good
> candidate). And if it does send a follow-up patch to convert your platform to
> the new implementation. If it does not please try to fix or add residue
> reporting support to your dmaengine driver.
> 
Will try it after adding cyclic tx_status support for mxs/imx dma driver.

Regards
Dong Aisheng

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