[pulseaudio-discuss] [PATCH 1/3] bluetooth: Do not switch to profile unless Playing

[Luiz Augusto von Dentz]

Hi Mikel, Tanu,

On Thu, Nov 24, 2011 at 5:05 PM, Mikel Astiz <mikel.astiz at bmw-carit.de> wrote:
> Hi Tanu,
>
> Thanks for your feedback.
>
>> So, my point is that even with your patch module-bluetooth-device may
>> choose to activate a2dp_source or hfgw, even if their state is just
>> "connected". I'm not an expert here, so I ask you: should the state checks
>> be changed also earlier in the function so that module-bluetooth-device
>> won't get loaded at all if the only connected profile is a2dp_source of
>> hfgw, and they are not yet in the "playing" state?
>
> The current approach seems to be that module-bluetooth-device will be loaded
> as long as the device exists and some audio profile is connected, which
> means the state is connected or playing. In a nutshell, the selected profile
> represents the interface that is actually playing.
>
> Even if a profile is in connected state (not playing), it does make sense to
> load the module, because then you have the option to change the profile from
> PA and effectively open an audio stream. This is useful for example in
> app-initiated audio connections, for example, streaming from phone to PC:
> the app switches the profile to a2dp_source, and the device simply starts to
> stream.
>
> The problem with this approach is that switching profiles has important
> side-effects, and must be considered with care. From my point of view, PA
> should ideally never switch a profile unless it knows it is safe and non
> app-specific. For this reason, this patch tries to set the initial profile
> according to the actual streaming state during discovery, but without
> opening new streams.

This depend on who is the initiator, if we are the initiator of the
connection then it may never enter PLAYING which can cause IOP
problems if we don't request a stream. Now there are recommendations
that a phone/source should open the stream not the carkit/sink but IMO
this should not be taken so literally as Ive seems some devices that
don't always behave as recommended.

> The patch does not solve the problem entirely since module-card-restore
> might still switch to a profile, but I was thinking of another patch to fix
> this second problem.

That sounds a better place to fix this, basically if we have a profile
in Playing state it should have the highest priority which should
prevent the profile switching.

-- 
Luiz Augusto von Dentz