Re: [PATCH v2 1/3] ALSA: pcm: add snd_pcm_period_elapsed() variant without acquiring lock of PCM substream

[Takashi Sakamoto <o-takashi@sakamocchi.jp>]

Hi,

On Thu, Jun 10, 2021 at 01:03:19PM +0200, Takashi Iwai wrote:
> On Thu, 10 Jun 2021 12:12:43 +0200, Takashi Sakamoto wrote:
> > 
> > On Thu, Jun 10, 2021 at 10:36:57AM +0200, Takashi Iwai wrote:
> > > Again, my *only* point is about the sleep.  You addition was:
> > > 
> > > + * Context: Any context in which lock of PCM substream is already acquired. This function may not
> > > + * sleep.
> > > 
> > > where "This function may not sleep" is stated incorrectly.
> > 
> > Hm. Would I request you to show the detail case that the call of function
> > (snd_pcm_period_elapsed_under_stream_lock()) goes sleep except for
> > driver-side implementation of snd_pcm_ops.{pointer, trigger,
> > get_time_info}? At least, in callgraph I find no function call to
> > yield...
> 
> True.  But the fact that those callbacks may sleep means that the
> function would go sleeping after all.

Thanks. After all, our discussion comes from the ambiguity that what
has responsibility at yielding processor under the lock. I think it helpful
to describe devide responsibilities about the yielding. I'm glad for you
to review patch below:

======== 8< --------

From 98e1b8332a95935ae875c637d3ddc27e68689aa0 Mon Sep 17 00:00:00 2001
From: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Date: Fri, 11 Jun 2021 11:03:46 +0900
Subject: [PATCH] ALSA: pcm: add context section for documentation about
 period-elapsed kernel APIs

This commit fulfils documentation of period-elapsed kernel APIs with their
context section.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
---
 sound/core/pcm_lib.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 7d5883432085..5d28d63a3216 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1803,6 +1803,10 @@ EXPORT_SYMBOL(snd_pcm_lib_ioctl);
  * - .get_time_info - to retrieve audio time stamp if needed.
  *
  * Even if more than one periods have elapsed since the last call, you have to call this only once.
+ *
+ * Context: Any context in which lock of PCM substream is already acquired. The function may not
+ * sleep by ALSA PCM core. The function may sleep in the above callbacks by driver which should
+ * configures PCM device for it (@snd_pcm.nonatomic).
  */
 void snd_pcm_period_elapsed_under_stream_lock(struct snd_pcm_substream *substream)
 {
@@ -1836,6 +1840,10 @@ EXPORT_SYMBOL(snd_pcm_period_elapsed_under_stream_lock);
  * It's typically called by any type of IRQ handler when hardware IRQ occurs to notify event that
  * the batch of audio data frames as the same size as the period of buffer is already processed in
  * audio data transmission.
+ *
+ * Context: Any context in which lock of PCM substream is not acquired yet. It depends on
+ * configuration of PCM device (@snd_pcm.nonatomic) by driver whether the function may or may not
+ * sleep by operating lock of PCM substream.
  */
 void snd_pcm_period_elapsed(struct snd_pcm_substream *substream)
 {
-- 
2.27.0

======== 8< --------

Thanks

Takashi Sakamoto