On 3/30/20 1:15 PM, Lars-Peter Clausen wrote:
On 3/30/20 7:52 PM, Stephan Gerhold wrote:
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).
q6asm-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.
Fixes: 2a9e92d371db ("ASoC: qdsp6: q6asm: Add q6asm dai driver")
Cc: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
Signed-off-by: Stephan Gerhold <stephan@xxxxxxxxxxx>
---
I'm still quite confused about the true meaning of SNDRV_PCM_INFO_BATCH,
so please correct me if I'm wrong :)
The meaning might have changed over the years, but the way it is used
right now is that it means that the position pointer has limited
granularity. With 'limited' being a bit fuzzy, but typically means that
the granularity is worse than a few samples.
This driver definitely falls into the limited category as the
granularity seems to be period size.
Agree, we added this INFO_BATCH flag for SOF Broadwell and Baytrail
platforms as well for the same reason of large granularity.
