ASoC: dmaengine-pcm: Add support for querying stream position from DMA driver

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.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/sound/dmaengine_pcm.h b/include/sound/dmaengine_pcm.h
index ea5791583fed..b877334bbb0f 100644
--- a/include/sound/dmaengine_pcm.h
+++ b/include/sound/dmaengine_pcm.h
@@ -38,6 +38,7 @@ void *snd_dmaengine_pcm_get_data(struct snd_pcm_substream *substream);
 int snd_hwparams_to_dma_slave_config(const struct snd_pcm_substream *substream,
         const struct snd_pcm_hw_params *params, struct dma_slave_config *slave_config);
 int snd_dmaengine_pcm_trigger(struct snd_pcm_substream *substream, int cmd);
+snd_pcm_uframes_t snd_dmaengine_pcm_pointer(struct snd_pcm_substream *substream);
 snd_pcm_uframes_t snd_dmaengine_pcm_pointer_no_residue(struct snd_pcm_substream *substream);
 
 int snd_dmaengine_pcm_open(struct snd_pcm_substream *substream,