ALSA: pcm: Skip ack callback without actual appl_ptr update

We call ack callback whenever appl_ptr gets updated via pcm_lib_apply_appl_ptr(). There are various code paths to call this function. A part of them are for read/write/forward/rewind, where the appl_ptr is always changed and thus the call of ack is mandatory. OTOH, another part of code paths are from the explicit user call, e.g. via SYNC_PTR ioctl. There, we may receive the same appl_ptr value, and in such a case, calling ack is obviously superfluous. This patch adds the check of the given appl_ptr value, and returns immediately if it's no real update. Reviewed-by: Takashi Sakamoto <[email protected]> Signed-off-by: Takashi Iwai <[email protected]>
CamonZ · Jun 14, 2017 · f8ff2f2 · f8ff2f2
1 parent 4e99151
commit f8ff2f2
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
@@ -2112,6 +2112,9 @@ int pcm_lib_apply_appl_ptr(struct snd_pcm_substream *substream,
 	snd_pcm_uframes_t old_appl_ptr = runtime->control->appl_ptr;
 	int ret;
 
+	if (old_appl_ptr == appl_ptr)
+		return 0;
+
 	runtime->control->appl_ptr = appl_ptr;
 	if (substream->ops->ack) {
 		ret = substream->ops->ack(substream);