Hello
This reverts a change that was part of a larger commit. That change broke timestamps in some application code for us as outlined in the log, and reverting it obviously fixes this. Since the original change did not explain why the behaviour was modified I can't speak for the effects on that use case.
Regards, /henrik
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Commit 3179f62001880e588e229db3006a59ad87b7792a ("ALSA: core: add .get_time_info") made an undocumented change to the behaviour of the PCM runtime tstamp. Prior to this change the tstamp was not updated by snd_pcm_update_hw_ptr0() unless the hw ptr had moved, after this change the tstamp is always updated.
For an application, using alsa-lib, doing snd_pcm_readi() followed by snd_pcm_status() to estimate the age of the read samples by subtracting status->avail * [sample rate] from status->tstamp this change degraded the accuracy of that estimate on devices where the pcm hw does not provide a granular hw pointer. On a device using soc-generic-dmaengine-pcm.c and a dma-engine with residue_granularity DMA_RESIDUE_GRANULARITY_DESCRIPTOR the accuracy of the estimate depended on the latency between the PCM hw completing a period and when the driver called snd_pcm_period_elapsed() to notify ALSA core, typically determined by interrupt handling latency. After this change the accuracy of the estimate is determined by the latency between the PCM hw completing a period and the application calling snd_pcm_status(), determined by the scheduling of the application process.
Revert the part of commit 3179f62001880e588e229db3006a59ad87b7792a ("ALSA: core: add .get_time_info") that changed be behaviour of snd_pcm_update_hw_ptr0() when the PCM hw pointer has not moved.
Fixes: 3179f6200188 ("ALSA: core: add .get_time_info") Signed-off-by: Henrik Eriksson henrik.eriksson@axis.com --- sound/core/pcm_lib.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c index a93a4235a332..2fbaf9a974cc 100644 --- a/sound/core/pcm_lib.c +++ b/sound/core/pcm_lib.c @@ -437,10 +437,8 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream, }
no_delta_check: - if (runtime->status->hw_ptr == new_hw_ptr) { - update_audio_tstamp(substream, &curr_tstamp, &audio_tstamp); + if (runtime->status->hw_ptr == new_hw_ptr) return 0; - }
if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK && runtime->silence_size > 0)