linux-kernel - Re: [RESEND PATCH] ALSA: dmaengine_pcm: terminate dmaengine before synchronize

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Date: Thu, 20 Jun 2024 09:57:00 +0200
From: Takashi Iwai <tiwai@...e.de>
To: Shengjiu Wang <shengjiu.wang@....com>
Cc: lars@...afoo.de,
	perex@...ex.cz,
	tiwai@...e.com,
	broonie@...nel.org,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	alsa-devel@...a-project.org,
	shengjiu.wang@...il.com
Subject: Re: [RESEND PATCH] ALSA: dmaengine_pcm: terminate dmaengine before synchronize

On Thu, 20 Jun 2024 04:40:18 +0200,
Shengjiu Wang wrote:
> 
> When dmaengine supports pause function, in suspend state,
> dmaengine_pause() is called instead of dmaengine_terminate_async(),
> 
> In end of playback stream, the runtime->state will go to
> SNDRV_PCM_STATE_DRAINING, if system suspend & resume happen
> at this time, application will not resume playback stream, the
> stream will be closed directly, the dmaengine_terminate_async()
> will not be called before the dmaengine_synchronize(), which
> violates the call sequence for dmaengine_synchronize().

Hmm, I can't follow this state change.
Do you mean that:
- snd_pcm_drain() is performed for a playback stream
- while draining operation, the system goes to suspend
- the system resumes (but the application doesn't call resume yet)
- The stream is closed (without calling resume)
??

If so, it's rather an inconsistent PCM state in the core side, and can
be fixed by a simple call like below:

-- 8< --
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2700,6 +2700,7 @@ void snd_pcm_release_substream(struct snd_pcm_substream *substream)
 	if (substream->ref_count > 0)
 		return;
 
+	snd_pcm_resume(substream);
 	snd_pcm_drop(substream);
 	if (substream->hw_opened) {
 		if (substream->runtime->state != SNDRV_PCM_STATE_OPEN)
-- 8< --

This will be no-op for the PCM device without SNDRV_PCM_INFO_RESUME.

But, this may need more rework, too; admittedly it imposes the
unnecessary resume of the stream although it shall be stopped and
closed immediately after that.  We may have some optimization in
addition.


thanks,

Takashi