linux-kernel - Re: [PATCH v2 3/3] ASoC: dmaengine-pcm: Add support for querying stream position from DMA driver

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Date:	Wed, 20 Jun 2012 16:25:33 +0530
From:	Vinod Koul <vinod.koul@...ux.intel.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>,
	Russell King <linux@....linux.org.uk>,
	Ola Lilja <ola.o.lilja@...ricsson.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Mika Westerberg <mika.westerberg@....fi>,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] ASoC: dmaengine-pcm: Add support for querying
 stream position from DMA driver

On Mon, 2012-06-11 at 20:11 +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 addresses the issue by
> implementing support for querying the current stream position directly from the
> dmaengine driver. Since not all dmaengine drivers support reporting the stream
> position yet the old period counting implementation is kept for now.
> 
> Furthermore the new mechanism allows to report the stream position with a
> sub-period granularity, given that the dmaengine driver supports this.
> 
Acked-by: Vinod Koul <vinod.koul@...el.com>

-- 
~Vinod

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