ASoC: amd: Modified DMA transfer Mechanism for Playback

Before rendering starts, DMA driver copies full buffer valid data
to ACP SRAM for the first time, after that ACP SRAM to I2S
FIFO DMA will be initiated. After rendering first half of ACP SRAM,
IOC will be raised then Audio data will be copied from first half of
System Memory to first half of ACP SRAM. Similarly after rendering
second half of ACP SRAM, IOC will be raised then Audio Data will be
copied from second half of the System Memory to second half of the
ACP SRAM in ping-pong way till rendering stops.

Old design introducing latency issues resulting stutter sound observed
during playback.
Signed-off-by: Vijendar Mukunda <Vijendar.Mukunda@amd.com>
Signed-off-by: Akshu Agrawal <Akshu.Agrawal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/amd/acp-pcm-dma.c

@@ -193,8 +193,8 @@ static void set_acp_sysmem_dma_descriptors(void __iomem *acp_mmio,
 		dmadscr[i].xfer_val = 0;
 		if (direction == SNDRV_PCM_STREAM_PLAYBACK) {
 			dma_dscr_idx = PLAYBACK_START_DMA_DESCR_CH12 + i;
-			dmadscr[i].dest = ACP_SHARED_RAM_BANK_1_ADDRESS +
-					(size / 2) - (i * (size/2));
+			dmadscr[i].dest = ACP_SHARED_RAM_BANK_1_ADDRESS
+					+ (i * (size/2));
 			dmadscr[i].src = ACP_INTERNAL_APERTURE_WINDOW_0_ADDRESS
 				+ (pte_offset * SZ_4K) + (i * (size/2));
 			switch (asic_type) {
@@ -655,9 +655,9 @@ static irqreturn_t dma_irq_handler(int irq, void *arg)
 		valid_irq = true;
 		if (acp_reg_read(acp_mmio, mmACP_DMA_CUR_DSCR_13) ==
 				PLAYBACK_START_DMA_DESCR_CH13)
-			dscr_idx = PLAYBACK_START_DMA_DESCR_CH12;
-		else
 			dscr_idx = PLAYBACK_END_DMA_DESCR_CH12;
+		else
+			dscr_idx = PLAYBACK_START_DMA_DESCR_CH12;
 		config_acp_dma_channel(acp_mmio, SYSRAM_TO_ACP_CH_NUM, dscr_idx,
 				       1, 0);
 		acp_dma_start(acp_mmio, SYSRAM_TO_ACP_CH_NUM, false);
@@ -882,23 +882,6 @@ static int acp_dma_prepare(struct snd_pcm_substream *substream)
 		config_acp_dma_channel(rtd->acp_mmio, ACP_TO_I2S_DMA_CH_NUM,
 					PLAYBACK_START_DMA_DESCR_CH13,
 					NUM_DSCRS_PER_CHANNEL, 0);
-		/* Fill ACP SRAM (2 periods) with zeros from System RAM
-		 * which is zero-ed in hw_params
-		*/
-		acp_dma_start(rtd->acp_mmio, SYSRAM_TO_ACP_CH_NUM, false);
-
-		/* ACP SRAM (2 periods of buffer size) is intially filled with
-		 * zeros. Before rendering starts, 2nd half of SRAM will be
-		 * filled with valid audio data DMA'ed from first half of system
-		 * RAM and 1st half of SRAM will be filled with Zeros. This is
-		 * the initial scenario when redering starts from SRAM. Later
-		 * on, 2nd half of system memory will be DMA'ed to 1st half of
-		 * SRAM, 1st half of system memory will be DMA'ed to 2nd half of
-		 * SRAM in ping-pong way till rendering stops.
-		*/
-		config_acp_dma_channel(rtd->acp_mmio, SYSRAM_TO_ACP_CH_NUM,
-					PLAYBACK_START_DMA_DESCR_CH12,
-					1, 0);
 	} else {
 		config_acp_dma_channel(rtd->acp_mmio, ACP_TO_SYSRAM_CH_NUM,
 					CAPTURE_START_DMA_DESCR_CH14,
@@ -913,7 +896,7 @@ static int acp_dma_prepare(struct snd_pcm_substream *substream)
 static int acp_dma_trigger(struct snd_pcm_substream *substream, int cmd)
 {
 	int ret;
-	u32 loops = 1000;
+	u32 loops = 4000;
 	u64 bytescount = 0;
 
 	struct snd_pcm_runtime *runtime = substream->runtime;