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, 34 insertions, 23 deletions

diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
index 6fd1906af387..6cef3977507a 100644
--- a/sound/soc/soc-generic-dmaengine-pcm.c
+++ b/sound/soc/soc-generic-dmaengine-pcm.c
@@ -163,31 +163,42 @@ static int dmaengine_pcm_set_runtime_hwparams(struct snd_pcm_substream *substrea
 	}
 
 	/*
-	 * Prepare formats mask for valid/allowed sample types. If the dma does
-	 * not have support for the given physical word size, it needs to be
-	 * masked out so user space can not use the format which produces
-	 * corrupted audio.
-	 * In case the dma driver does not implement the slave_caps the default
-	 * assumption is that it supports 1, 2 and 4 bytes widths.
+	 * If SND_DMAENGINE_PCM_DAI_FLAG_PACK is set keep
+	 * hw.formats set to 0, meaning no restrictions are in place.
+	 * In this case it's the responsibility of the DAI driver to
+	 * provide the supported format information.
 	 */
-	for (i = 0; i <= SNDRV_PCM_FORMAT_LAST; i++) {
-		int bits = snd_pcm_format_physical_width(i);
-
-		/* Enable only samples with DMA supported physical widths */
-		switch (bits) {
-		case 8:
-		case 16:
-		case 24:
-		case 32:
-		case 64:
-			if (addr_widths & (1 << (bits / 8)))
-				hw.formats |= (1LL << i);
-			break;
-		default:
-			/* Unsupported types */
-			break;
+	if (!(dma_data->flags & SND_DMAENGINE_PCM_DAI_FLAG_PACK))
+		/*
+		 * Prepare formats mask for valid/allowed sample types. If the
+		 * dma does not have support for the given physical word size,
+		 * it needs to be masked out so user space can not use the
+		 * format which produces corrupted audio.
+		 * In case the dma driver does not implement the slave_caps the
+		 * default assumption is that it supports 1, 2 and 4 bytes
+		 * widths.
+		 */
+		for (i = 0; i <= SNDRV_PCM_FORMAT_LAST; i++) {
+			int bits = snd_pcm_format_physical_width(i);
+
+			/*
+			 * Enable only samples with DMA supported physical
+			 * widths
+			 */
+			switch (bits) {
+			case 8:
+			case 16:
+			case 24:
+			case 32:
+			case 64:
+				if (addr_widths & (1 << (bits / 8)))
+					hw.formats |= (1LL << i);
+				break;
+			default:
+				/* Unsupported types */
+				break;
+			}
 		}
-	}
 
 	return snd_soc_set_runtime_hwparams(substream, &hw);
 }