[pulseaudio-discuss] [PATCH v0] bluetooth: Fix unacquired transports during sink resume

[Tanu Kaskinen]

On Tue, 2012-12-04 at 08:18 +0100, Mikel Astiz wrote:
> Hi Tanu,
> 
> On Tue, Dec 4, 2012 at 1:43 AM, Tanu Kaskinen <tanuk at iki.fi> wrote:
> > On Mon, 2012-12-03 at 10:57 +0100, Mikel Astiz wrote:
> >> On Sun, Dec 2, 2012 at 4:05 AM, Tanu Kaskinen <tanuk at iki.fi> wrote:
> >> > On Thu, 2012-11-29 at 14:33 +0100, Mikel Astiz wrote:
> >> >> On Thu, Nov 29, 2012 at 4:55 AM, Tanu Kaskinen <tanuk at iki.fi> wrote:
> >> >> > so that INIT->IDLE transitions will work too, if we decide some day that
> >> >> > it's not a good idea to start the devices suspended. (I think it makes
> >> >> > sense to start them suspended, but relying on module-suspend-on-idle for
> >> >> > unsuspending is not good.)
> >> >>
> >> >> INIT->IDLE should already be working, since in this case the transport
> >> >> is acquired before the thread is started. I just sent two patches
> >> >> that would do this for headsets, since Arun was
> >> >> also concerned about relying on the presence of
> >> >> module-suspend-on-idle.
> >> >
> >> > Would the acquire in setup_transport() be necessary at all if the
> >> > transport would be acquired in the PA_SINK_MESSAGE_SET_STATE handler
> >> > also for the INIT->IDLE transition?
> >>
> >> I believe that the acquire would always be necessary in
> >> setup_transport(), since this is the only way to find out which the
> >> initial state of the sink/sources should be.
> >
> > The initial state should always be IDLE for headsets, so in that case
> > there's nothing to decide, right? (Until the suspend-on-idle interaction
> > gets sorted out, that is.) For a2dp_source/hfgw, couldn't you figure out
> > the initial sink/source state from the bluetooth stream state instead of
> > checking whether the transport has been acquired? If the stream is not
> > playing, start suspended.
> 
> The issue is indeed about a2dp_source/hfgw.
> 
> The problem with checking the state before you acquire is that it's
> racy: by the time you reach MESSAGE_SET_STATE (or even worse, the
> BlueZ daemon) the state might have already changed. So the only real
> way to confirm that the audio is streaming by acquiring.

I see.

> This is not a strong argument for BlueZ 4.x since the D-Bus API does
> not support such atomic test&set acquisitions (optional acquire).
> That's why we have a FIXME in bt_transport_acquire(), where a similar
> behavior is simulated but is still racy. However, this has already
> been fixed for BlueZ 5 so I would suggest we continue with this
> approach, so we don't have to move more code around in the near
> future.

Yes, I agree.

-- 
Tanu