linux-kernel - [PATCH 3/8] ASoC: qcom: q6apm-dai: Add SNDRV_PCM_INFO

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Date:   Thu,  9 Feb 2023 12:28:01 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     broonie@...nel.org
Cc:     lgirdwood@...il.com, perex@...ex.cz, tiwai@...e.com,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        steev@...i.org, johan+linaro@...nel.org, quic_bjorande@...cinc.com,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: [PATCH 3/8]  ASoC: qcom: q6apm-dai: Add SNDRV_PCM_INFO_BATCH flag

At the moment, playing audio with PulseAudio with the qdsp6 driver
results in distorted sound. It seems like its timer-based scheduling
does not work properly with qdsp6 since setting tsched=0 in
the PulseAudio configuration avoids the issue.

Apparently this happens when the pointer() callback is not accurate
enough. There is a SNDRV_PCM_INFO_BATCH flag that can be used to stop
PulseAudio from using timer-based scheduling by default.

According to https://www.alsa-project.org/pipermail/alsa-devel/2014-March/073816.html:

The flag is being used in the sense explained in the previous audio
meeting -- the data transfer granularity isn't fine enough but aligned
to the period size (or less).

q6apm-dai reports the position as multiple of

prtd->pcm_count = snd_pcm_lib_period_bytes(substream)

so it indeed just a multiple of the period size.

Therefore adding the flag here seems appropriate and makes audio
work out of the box.

Comment log inspired by Stephan Gerhold sent for q6asm-dai.c few years back.

Fixes: 9b4fe0f1cd79 ("ASoC: qdsp6: audioreach: add q6apm-dai support")
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
---
 sound/soc/qcom/qdsp6/q6apm-dai.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/sound/soc/qcom/qdsp6/q6apm-dai.c b/sound/soc/qcom/qdsp6/q6apm-dai.c
index bd35067a4052..7f02f5b2c33f 100644
--- a/sound/soc/qcom/qdsp6/q6apm-dai.c
+++ b/sound/soc/qcom/qdsp6/q6apm-dai.c
@@ -64,7 +64,8 @@ struct q6apm_dai_data {
 static struct snd_pcm_hardware q6apm_dai_hardware_capture = {
 	.info =                 (SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_BLOCK_TRANSFER |
 				 SNDRV_PCM_INFO_MMAP_VALID | SNDRV_PCM_INFO_INTERLEAVED |
-				 SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME),
+				 SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME |
+				 SNDRV_PCM_INFO_BATCH),
 	.formats =              (SNDRV_PCM_FMTBIT_S16_LE | SNDRV_PCM_FMTBIT_S24_LE),
 	.rates =                SNDRV_PCM_RATE_8000_48000,
 	.rate_min =             8000,
@@ -82,7 +83,8 @@ static struct snd_pcm_hardware q6apm_dai_hardware_capture = {
 static struct snd_pcm_hardware q6apm_dai_hardware_playback = {
 	.info =                 (SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_BLOCK_TRANSFER |
 				 SNDRV_PCM_INFO_MMAP_VALID | SNDRV_PCM_INFO_INTERLEAVED |
-				 SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME),
+				 SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME |
+				 SNDRV_PCM_INFO_BATCH),
 	.formats =              (SNDRV_PCM_FMTBIT_S16_LE | SNDRV_PCM_FMTBIT_S24_LE),
 	.rates =                SNDRV_PCM_RATE_8000_192000,
 	.rate_min =             8000,
-- 
2.21.0