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

Vinod Koul vinod.koul at linux.intel.com
Wed Jun 20 12:55:33 CEST 2012

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 at intel.com>


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