Re: [PATCH] ALSA: pcm: Release paused streams before suspend if resume is not supported

[Takashi Iwai <tiwai@suse.de>]

On Wed, 02 Apr 2025 12:45:36 +0200,
Jaroslav Kysela wrote:
> 
> On 02. 04. 25 11:16, Takashi Iwai wrote:
> 
> >>>> For my view, the drivers may also receive those triggers:
> >>>> 
> >>>> SNDRV_PCM_TRIGGER_PAUSE_RELEASE_AND_STOP
> >>>> SNDRV_PCM_TRIGGER_SUSPEND_IN_PAUSE
> >>>> SNDRV_PCM_TRIGGER_RELEASE_IN_PAUSE
> >>>> 
> >>>> This will allow to handle all states properly without any side effects
> >>>> (like short unwanted DMA transfers).
> >>>> 
> >>>> The drivers should probably activate those triggers conditionally to
> >>>> not break current state sequences.
> >>> 
> >>> Hmm, that looks too complex, IMO.
> >>> 
> >>> Another slightly more straightforward fix would be just to allow the
> >>> direct state transition from PAUSED to any state.  Then the remaining
> >>> piece is all about driver implementations.  And, this can be
> >>> conditionally operated, e.g. only when some extra flag is set.  When
> >>> no flag is set, we keep applying PAUSE_RELEASE before the transition
> >>> like now, including Peter's patch, that can work generically (but not
> >>> always ideally).
> >> 
> >> It looks also feasible. My proposal just allows the straight state
> >> identification from the trigger value in the drivers.
> > 
> > On the second thought, yet another variant would be to introduce only
> > one new trigger, SNDRV_PCM_TRIGGER_PAUSE_RESET, for resetting the
> > PAUSED state as a step before stopping the stream.  This can be
> > applied to all cases for snd_pcm_drop() and snd_pcm_suspend(), too.
> > If the driver doesn't support this mode, the PCM core may fall back to
> > SNDRV_PCM_TRIGGER_PAUSE_RELEASE.
> 
> This looks identical to my proposed
> SNDRV_PCM_TRIGGER_PAUSE_RELEASE_AND_STOP which is more
> explanatory. It's not clear what PAUSE_RESET should do (probably the
> stream should be kept inactive).

There is a slight difference.  My proposal, *_TRIGGER_PAUSE_RESET,
doesn't have to stop the stream by itself, but it's only a preparation
for stopping.  That is, a proper TRIGGER_STOP always follows after
TRIGGER_PAUSE_RESET.


thanks,

Takashi