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ALSA: pcm: Comment why read blocks when PCM is not running 

This avoids bringing back the problem introduced by
62ba568f7a ("ALSA: pcm: Return 0 when size <
start_threshold in capture") and fixed in 00a399cad1
("ALSA: pcm: Revert capture stream behavior change in
blocking mode"), which prevented the user from starting
capture from another thread.

Signed-off-by: Ricardo Biehl Pasquali <pasqualirb@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Ricardo Biehl Pasquali 2019-02-13 00:57:51 -02:00 committed by Takashi Iwai
parent 5a23f38568
commit 932a815195
1 changed files with 4 additions and 0 deletions
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4
sound/core/pcm_lib.c
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@ -2176,6 +2176,10 @@ snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream,
if (runtime->status->state == SNDRV_PCM_STATE_RUNNING)
snd_pcm_update_hw_ptr(substream);
/*
* If size < start_threshold, wait indefinitely. Another
* thread may start capture
*/
if (!is_playback &&
runtime->status->state == SNDRV_PCM_STATE_PREPARED &&
size >= runtime->start_threshold) {