ASoC: dmaengine_pcm: Add support for packed transfers

dmaengine_pcm currently only supports setups where FIFO reads/writes
correspond to exactly one sample, eg 16-bit sample data is transferred
via 16-bit FIFO accesses, 32-bit data via 32-bit accesses.

This patch adds support for setups with fixed width FIFOs where
multiple samples are packed into a larger word.

For example setups with a 32-bit wide FIFO register that expect
16-bit sample transfers to be done with the left+right sample data
packed into a 32-bit word.

Support for packed transfers is controlled via the
SND_DMAENGINE_PCM_DAI_FLAG_PACK flag in snd_dmaengine_dai_dma_data.flags

If this flag is set dmaengine_pcm doesn't put any restriction on the
supported formats and sets the DMA transfer width to undefined.

This means control over the constraints is now transferred to the DAI
driver and it's responsible to provide proper configuration and
check for possible corner cases that aren't handled by the ALSA core.

Signed-off-by: Matthias Reichl <hias@horus.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Tested-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/sound/dmaengine_pcm.h b/include/sound/dmaengine_pcm.h
index f86ef5ea9b01..67be2445941a 100644
--- a/include/sound/dmaengine_pcm.h
+++ b/include/sound/dmaengine_pcm.h
@@ -51,6 +51,16 @@ struct dma_chan *snd_dmaengine_pcm_request_channel(dma_filter_fn filter_fn,
 	void *filter_data);
 struct dma_chan *snd_dmaengine_pcm_get_chan(struct snd_pcm_substream *substream);
 
+/*
+ * The DAI supports packed transfers, eg 2 16-bit samples in a 32-bit word.
+ * If this flag is set the dmaengine driver won't put any restriction on
+ * the supported sample formats and set the DMA transfer size to undefined.
+ * The DAI driver is responsible to disable any unsupported formats in it's
+ * configuration and catch corner cases that are not already handled in
+ * the ALSA core.
+ */
+#define SND_DMAENGINE_PCM_DAI_FLAG_PACK BIT(0)
+
 /**
  * struct snd_dmaengine_dai_dma_data - DAI DMA configuration data
  * @addr: Address of the DAI data source or destination register.
@@ -63,6 +73,7 @@ struct dma_chan *snd_dmaengine_pcm_get_chan(struct snd_pcm_substream *substream)
  * requesting the DMA channel.
  * @chan_name: Custom channel name to use when requesting DMA channel.
  * @fifo_size: FIFO size of the DAI controller in bytes
+ * @flags: PCM_DAI flags, only SND_DMAENGINE_PCM_DAI_FLAG_PACK for now
  */
 struct snd_dmaengine_dai_dma_data {
 	dma_addr_t addr;
@@ -72,6 +83,7 @@ struct snd_dmaengine_dai_dma_data {
 	void *filter_data;
 	const char *chan_name;
 	unsigned int fifo_size;
+	unsigned int flags;
 };
 
 void snd_dmaengine_pcm_set_config_from_dai_data(