ASoC: rsnd: dma: set bus width to data width for monaural data

According to R-Car3 HW manual 40.3.3 (Data Format on Audio Local Bus),
in case of monaural data writing or reading through Audio-DMAC,
it's always in Left Justified format, so both src and dst
DMA Bus width should be equal to physical data width.

Therefore set src and dst's DMA bus width to:
 - [monaural case] data width
 - [non-monaural case] 32bits (as prior applying the patch)

Cc: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Cc: Timo Wischer <twischer@de.adit-jv.com>
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Link: https://lore.kernel.org/r/20191022185518.12838-1-erosca@de.adit-jv.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sh/rcar/dma.c

@@ -165,14 +165,40 @@ static int rsnd_dmaen_start(struct rsnd_mod *mod,
 	struct device *dev = rsnd_priv_to_dev(priv);
 	struct dma_async_tx_descriptor *desc;
 	struct dma_slave_config cfg = {};
+	enum dma_slave_buswidth buswidth = DMA_SLAVE_BUSWIDTH_4_BYTES;
 	int is_play = rsnd_io_is_play(io);
 	int ret;
 
+	/*
+	 * in case of monaural data writing or reading through Audio-DMAC
+	 * data is always in Left Justified format, so both src and dst
+	 * DMA Bus width need to be set equal to physical data width.
+	 */
+	if (rsnd_runtime_channel_original(io) == 1) {
+		struct snd_pcm_runtime *runtime = rsnd_io_to_runtime(io);
+		int bits = snd_pcm_format_physical_width(runtime->format);
+
+		switch (bits) {
+		case 8:
+			buswidth = DMA_SLAVE_BUSWIDTH_1_BYTE;
+			break;
+		case 16:
+			buswidth = DMA_SLAVE_BUSWIDTH_2_BYTES;
+			break;
+		case 32:
+			buswidth = DMA_SLAVE_BUSWIDTH_4_BYTES;
+			break;
+		default:
+			dev_err(dev, "invalid format width %d\n", bits);
+			return -EINVAL;
+		}
+	}
+
 	cfg.direction	= is_play ? DMA_MEM_TO_DEV : DMA_DEV_TO_MEM;
 	cfg.src_addr	= dma->src_addr;
 	cfg.dst_addr	= dma->dst_addr;
-	cfg.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
-	cfg.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
+	cfg.src_addr_width = buswidth;
+	cfg.dst_addr_width = buswidth;
 
 	dev_dbg(dev, "%s %pad -> %pad\n",
 		rsnd_mod_name(mod),