On Jun 19 2017 02:23, Takashi Iwai wrote:
I'll post a patch to take 'snd_pcm_reset()' to use
'snd_pcm_action_lock_irq()' instead of
'snd_pcm_action_nonatomic()'. How do you think about it?
Conceptually seen, that's not right. snd_pcm_reset() calls PCM ioctl
ops, and this is supposed to be always non-atomic (it's a kind of
ioctl wrapper, after all). So the correct fix would be simply to wrap
only the snd_pcm_playback_silence() call with the stream lock.
I once investigated for this idea. But I was discouraged because of
several resons:
1. There's a semantic contradiction. 'snd_pcm_action_nonatomic()'
includes atomic operation. The idea perhaps puzzles developers.
2. In 'snd_pcm_pre_reset()', 'snd_pcm_do_reset()' and
'snd_pcm_post_reset()', parameters of runtime for PCM substream are also
changed or referred. They can be changed in other functions
concurrently, thus should be locked.
3. Currently there're a few drivers which implements the local ioctl.
All of them handle the callback without calling task scheduler. It's
reasonable against the cost to have an additional restraint just for
context with the reset command.
Well, this is a revised version.
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 7e8f3656b695..c74bee099155 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -1593,7 +1593,11 @@ static int snd_pcm_pre_reset(struct
snd_pcm_substream *substream, int state)
static int snd_pcm_do_reset(struct snd_pcm_substream *substream, int
state)
{
struct snd_pcm_runtime *runtime = substream->runtime;
- int err = substream->ops->ioctl(substream,
SNDRV_PCM_IOCTL1_RESET, NULL);
+ int err;
+
+ snd_pcm_stream_unlock_irq(substream);
+ err = substream->ops->ioctl(substream, SNDRV_PCM_IOCTL1_RESET,
NULL);
+ snd_pcm_stream_lock_irq(substream);
if (err < 0)
return err;
runtime->hw_ptr_base = 0;
@@ -1621,7 +1625,7 @@ static const struct action_ops
snd_pcm_action_reset = {
static int snd_pcm_reset(struct snd_pcm_substream *substream)
{
- return snd_pcm_action_nonatomic(&snd_pcm_action_reset,
substream, 0);
+ return snd_pcm_action_lock_irq(&snd_pcm_action_reset, substream, 0);
}
/*
There's still a contradiction about atomicity but as a whole better than
before.
Regards
Takashi Sakamoto
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
