Re: [alsa-devel] [PATCH] ASoC: Intel: Atom: read timestamp moved to period_elapsed

From: Pierre-Louis Bossart
Date: Wed Jul 17 2019 - 11:30:33 EST

On 7/10/19 6:15 PM, Curtis Malainey wrote:
On Tue, Jul 9, 2019 at 4:45 AM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:

On Mon, Jul 08, 2019 at 09:01:47PM -0700, Alex Levin wrote:
sst_platform_pcm_pointer is called from both snd_pcm_period_elapsed and
from snd_pcm_ioctl. Calling read timestamp results in recalculating
pcm_delay and buffer_ptr (sst_calc_tstamp) which consumes buffers in a
faster rate than intended.
In a tested BSW system with chtrt5650, for a rate of 48000, the
measured rate was sometimes 10 times more than that.
After moving the timestamp read to period elapsed, buffer consumption is
as expected.

From code prospective it looks good. You may take mine
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

Though I'm not an expert in the area, Pierre and / or Liam should give
their blessing.

Agreed, Liam or Pierre should also give their ok since this is one of
the closed source firmware drivers.

Reviewed-by: Curtis Malainey <cujomalainey@xxxxxxxxxxxx>

Humm, this first review after my Summer break isn't straightforward.

By moving the timestamp update to the period elapsed event, don't you prevent the use of this driver in no-interrupt mode - which I understood as the baseline for Chrome?

And I also don't get how this timestamp might lead to 10x speed issues, this driver has been around for a number of years and that specific error was never seen. What is different in this platform and can this be seen e.g. on a Cyan device?

Signed-off-by: Alex Levin <levinale@xxxxxxxxxxxx>
sound/soc/intel/atom/sst-mfld-platform-pcm.c | 23 +++++++++++++-------
1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/sound/soc/intel/atom/sst-mfld-platform-pcm.c b/sound/soc/intel/atom/sst-mfld-platform-pcm.c
index 0e8b1c5eec88..196af0b30b41 100644
--- a/sound/soc/intel/atom/sst-mfld-platform-pcm.c
+++ b/sound/soc/intel/atom/sst-mfld-platform-pcm.c
@@ -265,16 +265,28 @@ static void sst_period_elapsed(void *arg)
struct snd_pcm_substream *substream = arg;
struct sst_runtime_stream *stream;
- int status;
+ struct snd_soc_pcm_runtime *rtd;
+ int status, ret_val;

if (!substream || !substream->runtime)
stream = substream->runtime->private_data;
if (!stream)
+ rtd = substream->private_data;
+ if (!rtd)
+ return;
status = sst_get_stream_status(stream);
+ ret_val = stream->ops->stream_read_tstamp(sst->dev, &stream->stream_info);
+ if (ret_val) {
+ dev_err(rtd->dev, "stream_read_tstamp err code = %d\n", ret_val);
+ return;
+ }

@@ -658,20 +670,15 @@ static snd_pcm_uframes_t sst_platform_pcm_pointer
(struct snd_pcm_substream *substream)
struct sst_runtime_stream *stream;
- int ret_val, status;
+ int status;
struct pcm_stream_info *str_info;
- struct snd_soc_pcm_runtime *rtd = substream->private_data;

stream = substream->runtime->private_data;
status = sst_get_stream_status(stream);
if (status == SST_PLATFORM_INIT)
return 0;
str_info = &stream->stream_info;
- ret_val = stream->ops->stream_read_tstamp(sst->dev, str_info);
- if (ret_val) {
- dev_err(rtd->dev, "sst: error code = %d\n", ret_val);
- return ret_val;
- }
substream->runtime->delay = str_info->pcm_delay;
return str_info->buffer_ptr;

With Best Regards,
Andy Shevchenko

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