[PATCH 4.19 176/361] ASoC: AMD: Fix capture unstable in beginning for some runs

[Greg Kroah-Hartman]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Akshu Agrawal <akshu.agrawal@xxxxxxx>

[ Upstream commit c50535ed6a10fcae1b64ae83c0f6b1eeb5535afc ]

alsa_conformance_test -C hw:0,4 -p 1024 --debug
would sometime show:
TIME_DIFF(s)    HW_LEVEL       READ              RATE
0.000095970         1024       1024    10670001.041992
0.042609555         1024       2048       24032.168372
0.021330364         1024       3072       48006.681930
0.021339559         1024       4096       47985.996337
The issue is that in dma pointer function we can have stale value
of the register for current descriptor of channel.
The register retains the number of the last descriptor that
was transferred.

Fix ensures that we report position, 0, till the one period worth of
data is transferred.  After one period of data, in handler of period
completion interrupt we update the config and correct value of descriptor
starts reflecting.

Signed-off-by: Akshu Agrawal <akshu.agrawal@xxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 sound/soc/amd/acp-pcm-dma.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--- a/sound/soc/amd/acp-pcm-dma.c
+++ b/sound/soc/amd/acp-pcm-dma.c
@@ -1036,16 +1036,22 @@ static snd_pcm_uframes_t acp_dma_pointer
 
 	if (substream->stream == SNDRV_PCM_STREAM_CAPTURE) {
 		period_bytes = frames_to_bytes(runtime, runtime->period_size);
-		dscr = acp_reg_read(rtd->acp_mmio, rtd->dma_curr_dscr);
-		if (dscr == rtd->dma_dscr_idx_1)
-			pos = period_bytes;
-		else
-			pos = 0;
 		bytescount = acp_get_byte_count(rtd);
-		if (bytescount > rtd->bytescount)
+		if (bytescount >= rtd->bytescount)
 			bytescount -= rtd->bytescount;
-		delay = do_div(bytescount, period_bytes);
-		runtime->delay = bytes_to_frames(runtime, delay);
+		if (bytescount < period_bytes) {
+			pos = 0;
+		} else {
+			dscr = acp_reg_read(rtd->acp_mmio, rtd->dma_curr_dscr);
+			if (dscr == rtd->dma_dscr_idx_1)
+				pos = period_bytes;
+			else
+				pos = 0;
+		}
+		if (bytescount > 0) {
+			delay = do_div(bytescount, period_bytes);
+			runtime->delay = bytes_to_frames(runtime, delay);
+		}
 	} else {
 		buffersize = frames_to_bytes(runtime, runtime->buffer_size);
 		bytescount = acp_get_byte_count(rtd);