Commit beff053c authored Apr 27, 2016 by Matthias Reichl Committed by Mark Brown Apr 27, 2016

ASoC: bcm2835: Add S16_LE support via packed DMA transfers



The bcm2835-i2s driver already has support for the S16_LE format but
that format hasn't been made available because dmaengine_pcm didn't
support packed data transfers.

bcm2835-i2s needs 16-bit left+right channel data to be packed into
a 32-bit word, the FIFO register is 32-bit only and doesn't support
16-bit access.

Now that dmaengine_pcm supports packed transfers the format can
be made available by setting the SND_DMAENGINE_PCM_DAI_FLAG_PACK flag.

No further configuration is necessary:
- snd_dmaengine_dai_dma_data.addr_width is already set to
  DMA_SLAVE_BUSWIDTH_4_BYTES to force 32-bit DMA transfers
- dmaengine_pcm will pick up the S16_LE format from the DAI
  configuration and make it available since it's no longer
  masked out due to the PACK flag.
- there are no further corner cases to catch in hw_params,
  since the channel count is fixed at 2 we always have two
  16-bit stereo samples that can be transferred via 32-bit DMA

Signed-off-by: Matthias Reichl <hias@horus.com>
Tested-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

parent cc70666c

sound/soc/bcm/bcm2835-i2s.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -690,6 +690,15 @@ static int bcm2835_i2s_probe(struct platform_device *pdev)
		dev->dma_data[SNDRV_PCM_STREAM_PLAYBACK].maxburst = 2;
		dev->dma_data[SNDRV_PCM_STREAM_CAPTURE].maxburst = 2;

		/*
		* Set the PACK flag to enable S16_LE support (2 S16_LE values
		* packed into 32-bit transfers).
		*/
		dev->dma_data[SNDRV_PCM_STREAM_PLAYBACK].flags =
		SND_DMAENGINE_PCM_DAI_FLAG_PACK;
		dev->dma_data[SNDRV_PCM_STREAM_CAPTURE].flags =
		SND_DMAENGINE_PCM_DAI_FLAG_PACK;

		/* BCLK ratio - use default */
		dev->bclk_ratio = 0;