[pulseaudio-discuss] [PATCH 1/2] sink, source: Add a flag to inhibit suspend

[Tanu Kaskinen]

On Thu, 2013-08-08 at 12:09 +0530, Arun Raghavan wrote:
> On Thu, 2013-08-08 at 09:07 +0300, Tanu Kaskinen wrote:
> > On Thu, 2013-08-08 at 10:53 +0530, Arun Raghavan wrote:
> > > This adds the ability to inhibit the suspending of a sink/source. Policy
> > > modules may override this, but should avoid doing so if they can.
> > > ---
> > >  src/pulse/def.h        | 6 ++++++
> > >  src/pulsecore/sink.c   | 3 +++
> > >  src/pulsecore/source.c | 3 +++
> > >  3 files changed, 12 insertions(+)
> > > 
> > > diff --git a/src/pulse/def.h b/src/pulse/def.h
> > > index 58190cb..11f5cb2 100644
> > > --- a/src/pulse/def.h
> > > +++ b/src/pulse/def.h
> > > @@ -795,6 +795,9 @@ typedef enum pa_sink_flags {
> > >  
> > >      PA_SINK_DEFERRED_VOLUME = 0x2000000U,
> > >      /**< The HW volume changes are syncronized with SW volume. */
> > > +
> > > +    PA_SINK_ALWAYS_RUNNING = 0x4000000U,
> > > +    /**< The sink should not be automatically suspended. */
> > >  /** \endcond */
> > >  #endif
> > >  
> > > @@ -914,6 +917,9 @@ typedef enum pa_source_flags {
> > >  
> > >      PA_SOURCE_DEFERRED_VOLUME = 0x2000000U,
> > >      /**< The HW volume changes are syncronized with SW volume. */
> > > +
> > > +    PA_SOURCE_ALWAYS_RUNNING = 0x4000000U,
> > > +    /**< The source should not be automatically suspended. */
> > >  #endif
> > >  } pa_source_flags_t;
> > >  
> > > diff --git a/src/pulsecore/sink.c b/src/pulsecore/sink.c
> > > index 00bc29a..9ebf4ce 100644
> > > --- a/src/pulsecore/sink.c
> > > +++ b/src/pulsecore/sink.c
> > > @@ -834,6 +834,9 @@ int pa_sink_suspend(pa_sink *s, bool suspend, pa_suspend_cause_t cause) {
> > >      pa_assert(PA_SINK_IS_LINKED(s->state));
> > >      pa_assert(cause != 0);
> > >  
> > > +    if ((s->flags & PA_SINK_ALWAYS_RUNNING) && (cause == PA_SUSPEND_IDLE))
> > > +        return 0;
> > 
> > Shouldn't the return value be -1?
> > 
> > This assumes that if ALWAYS_RUNNING is set, then the IDLE cause can't
> > appear together with other causes. I think that's a valid assumption,
> > though, so I don't have a problem with that. Avoiding that assumption
> > would require deciding what to do when one suspend cause is not allowed
> > and one is, and I don't want to form an opinion about that.
> 
> My thinking was basically that this is not an error. A policy module
> said "go ahead and suspend this sink, I think it's not needed", while
> some other policy asserted "nope, don't ever suspend this sink". So it's
> not an error but a behaviour override.

I disagree. ALWAYS_RUNNING is set by hw adaptation code, and the hw
adaptation shouldn't have any say in the policy. I think the
ALWAYS_RUNNING flag describes the hardware, it says "if you suspend this
sink needlessly, bad things will happen". The flag is not part of the
policy configuration. ALWAYS_RUNNING does sound like a policy flag,
though, so I think AVOID_UNNECESSARY_SUSPENDING would be a better name.

Some policy module asked the sink to suspend with the IDLE cause, and
that operation was not allowed, so I think it makes sense to tell the
policy module that its request was denied.

> As for chained suspend causes, the intention of this patch was to only
> ignore idle suspend. If something else wants to force a suspend, I think
> it should be honoured. That is, the check should be filter out the IDLE
> cause if cause is IDLE+<something else>.

I think we shouldn't prepare for IDLE+<something else>, because we don't
need to and it would bring some complications as I explained in the
previous mail.

> > This also assumes that if ALWAYS_RUNNING is set, then s->suspend_cause
> > can't contain IDLE, because this blocks also unsuspending with the IDLE
> > cause. I think it would be better to avoid this assumption by not
> > failing when unsuspending.
> 
> Or we do the thing I stated above and (David's going to hate me) add an
> assert for this case. If something's modifying that suspend cause and
> it's not pa_sink_suspend(), we probably want to catch it and either make
> it not do that or make sure it's handling this flag correctly.

A sink might want to start suspended, in which case pa_sink_suspend()
wouldn't be called.

-- 
Tanu