ASoC: Revert "Drop SND_DMAENGINE_PCM_FLAG_CUSTOM_CHANNEL_NAME flag"

This reverts commit c6644119 and
restores the ability to specify DMA channel names per DAI dma_data.
Unfortunately the functionality removed in the patch being reverted
cannot be entirely replaced by specifying DMA channel names in struct
snd_dmaengine_pcm_config as that does not cover devices with more than
2 DMA channels.

Together with patch "ASoC: Revert "samsung: Remove unneeded
initialization of chan_name"" this fixes broken sound on the s3c24xx
SoC platforms.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/sound/dmaengine_pcm.h

@@ -71,6 +71,7 @@ struct dma_chan *snd_dmaengine_pcm_get_chan(struct snd_pcm_substream *substream)
  * @slave_id: Slave requester id for the DMA channel.
  * @filter_data: Custom DMA channel filter data, this will usually be used when
  * 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
  */
@@ -80,6 +81,7 @@ struct snd_dmaengine_dai_dma_data {
 	u32 maxburst;
 	unsigned int slave_id;
 	void *filter_data;
+	const char *chan_name;
 	unsigned int fifo_size;
 	unsigned int flags;
 };
@@ -105,6 +107,10 @@ void snd_dmaengine_pcm_set_config_from_dai_data(
  * playback.
  */
 #define SND_DMAENGINE_PCM_FLAG_HALF_DUPLEX BIT(3)
+/*
+ * The PCM streams have custom channel names specified.
+ */
+#define SND_DMAENGINE_PCM_FLAG_CUSTOM_CHANNEL_NAME BIT(4)
 
 /**
  * struct snd_dmaengine_pcm_config - Configuration data for dmaengine based PCM

sound/soc/soc-generic-dmaengine-pcm.c

@@ -263,6 +263,7 @@ static int dmaengine_pcm_new(struct snd_soc_pcm_runtime *rtd)
 	struct dmaengine_pcm *pcm = soc_platform_to_pcm(rtd->platform);
 	const struct snd_dmaengine_pcm_config *config = pcm->config;
 	struct device *dev = rtd->platform->dev;
+	struct snd_dmaengine_dai_dma_data *dma_data;
 	struct snd_pcm_substream *substream;
 	size_t prealloc_buffer_size;
 	size_t max_buffer_size;
@@ -282,6 +283,13 @@ static int dmaengine_pcm_new(struct snd_soc_pcm_runtime *rtd)
 		if (!substream)
 			continue;
 
+		dma_data = snd_soc_dai_get_dma_data(rtd->cpu_dai, substream);
+
+		if (!pcm->chan[i] &&
+		    (pcm->flags & SND_DMAENGINE_PCM_FLAG_CUSTOM_CHANNEL_NAME))
+			pcm->chan[i] = dma_request_slave_channel(dev,
+				dma_data->chan_name);
+
 		if (!pcm->chan[i] && (pcm->flags & SND_DMAENGINE_PCM_FLAG_COMPAT)) {
 			pcm->chan[i] = dmaengine_pcm_compat_request_channel(rtd,
 				substream);
@@ -350,7 +358,9 @@ static int dmaengine_pcm_request_chan_of(struct dmaengine_pcm *pcm,
 	const char *name;
 	struct dma_chan *chan;
 
-	if ((pcm->flags & SND_DMAENGINE_PCM_FLAG_NO_DT) || !dev->of_node)
+	if ((pcm->flags & (SND_DMAENGINE_PCM_FLAG_NO_DT |
+			   SND_DMAENGINE_PCM_FLAG_CUSTOM_CHANNEL_NAME)) ||
+	    !dev->of_node)
 		return 0;
 
 	if (config && config->dma_dev) {