[pulseaudio-discuss] [PATCH v13 10/10] bluetooth: policy: Treat bi-directional A2DP profiles as suitable for VOIP

Tue Oct 29 10:42:51 UTC 2019

On Tuesday 29 October 2019 11:24:06 Hyperion wrote:
> 
> 
> 29.10.2019, 10:24, "Pali Rohár" <pali.rohar at gmail.com>:
> > On Monday 28 October 2019 17:12:45 Hyperion wrote:
> >>  28.10.2019, 16:11, "Tanu Kaskinen" <tanuk at iki.fi>:
> >>  > On Sat, 2019-10-26 at 20:23 +0200, Hyperion wrote:
> >>  >>  26.10.2019, 14:39, "Tanu Kaskinen" <tanuk at iki.fi>:
> >>  >>  > On Sat, 2019-10-19 at 18:42 +0200, Pali Rohár wrote:
> >>  >>  > > On Saturday 19 October 2019 19:27:19 Tanu Kaskinen wrote:
> >>  >>  > > > On Sat, 2019-10-19 at 18:16 +0200, Pali Rohár wrote:
> >>  >>  > > > > On Saturday 19 October 2019 19:07:44 Tanu Kaskinen wrote:
> >>  >>  > > > > > On Sat, 2019-10-19 at 17:20 +0200, Pali Rohár wrote:
> >>  >>  > > > > > > On Friday 18 October 2019 15:29:43 Tanu Kaskinen wrote:
> >>  >>  > > > > > > > On Thu, 2019-10-17 at 15:34 +0200, Hyperion wrote:
> >>  >>  > > > > > > > > Regression would mean that some devices can't connect anymore : this
> >>  >>  > > > > > > > > won't happen if a workaround is provided, and this workaround won't
> >>  >>  > > > > > > > > be used often.
> >>  >>  > > > > > > > >
> >>  >>  > > > > > > > > Most (99% ?) of the devices will work correctly with my patch (many
> >>  >>  > > > > > > > > of them in XQ mode, and some in legacy mode because they will fall
> >>  >>  > > > > > > > > back to legacy bitpool during negociation)
> >>  >>  > > > > > > > >
> >>  >>  > > > > > > > > The remaining (1% ?) : will need a simple boolean swicth in one of
> >>  >>  > > > > > > > > the PA config files to restrict negociation to legacy bitpool (a
> >>  >>  > > > > > > > > module option ? or daemon.conf ?).
> >>  >>  > > > > > > > >
> >>  >>  > > > > > > > > I think it's really "simple", efficient, and not dependent of any
> >>  >>  > > > > > > > > upcoming Bluez feature.
> >>  >>  > > > > > > > >
> >>  >>  > > > > > > > > "The complex solution is always the best until one find a simpler one"
> >>  >>  > > > > > > >
> >>  >>  > > > > > > > I don't know the number of users who use bluetooth headsets with
> >>  >>  > > > > > > > PulseAudio, but even just 1% regression rate can mean quite a few
> >>  >>  > > > > > > > unhappy users. When your headset suddenly stops working, it's not
> >>  >>  > > > > > > > trivial to figure out that you may need to pass a special argument to
> >>  >>  > > > > > > > module-bluetooth-discover in order to make it work again.
> >>  >>  > > > > > > >
> >>  >>  > > > > > > > It would be better to have a module argument to enable the XQ settings.
> >>  >>  > > > > > >
> >>  >>  > > > > > > Main question, do we really need this special "settings"? Because my
> >>  >>  > > > > > > patch series introduce also SBC XQ profile and basically replaces above
> >>  >>  > > > > > > module parameter, by runtime configuration.
> >>  >>  > > > > > >
> >>  >>  > > > > > > For me above solution looks like a hack. It adds some module parameter
> >>  >>  > > > > > > for tweaking configuration. And what would happen with that parameter
> >>  >>  > > > > > > after we have "proper" support for multiple codecs? Do we need to
> >>  >>  > > > > > > maintain backward compatibility? Or would we remove that configuration
> >>  >>  > > > > > > and therefore revert to state prior existence of new module parameter
> >>  >>  > > > > > > (which is current situation)?
> >>  >>  > > > > >
> >>  >>  > > > > > After your patches there's still the "automatic bitpool" mode
> >>  >>  > > > > > available, right?
> >>  >>  > > > >
> >>  >>  > > > > Yes, I wanted to have it there for legacy/backward compatibility reasons
> >>  >>  > > > > for those devices which could be broken with new settings. That is the
> >>  >>  > > > > reason I do not wanted to touch Automatic mode, to have exact same
> >>  >>  > > > > behavior as in current (and older) pulseaudio versions.
> >>  >>  > > > >
> >>  >>  > > > > But if automatic mode is going to be changed, I do not see reason for
> >>  >>  > > > > keeping it (the argument for backward compatibility would not apply
> >>  >>  > > > > anymore, if it is going to be changed). My patch series with new A2DP
> >>  >>  > > > > API can fully replace that automatic mode.
> >>  >>  > > >
> >>  >>  > > > I don't see how the proposed option changes anything about
> >>  >>  > > > compatibility. The option will be disabled by default, so the default
> >>  >>  > > > behaviour will be the same as always.
> >>  >>  > >
> >>  >>  > > And what should happen after support for multiple A2DP codecs (from my
> >>  >>  > > patch series) would be there? Basically it obsoletes that config option.
> >>  >>  > > As all such settings can be set at runtime.
> >>  >>  >
> >>  >>  > If the "enable XQ in the automatic bitpool mode" option is made run-
> >>  >>  > time configurable, then yes, the module argument will become obsolete.
> >>  >>
> >>  >>  I don't think so : by default Pali's patch first connects using one of the 2 XQ modes : so
> >>  >>  it will fail with devices not "XQ able". Since we are having this discussion only because
> >>  >>  we don't want ANY regression (even as rare as the devices that can't do bitpool 38 dual
> >>  >>  , and even for users who don't know how to switch SBC modes) : then the default mode
> >>  >>  of operations shouldn't allow XQ at all.
> >>  >
> >>  > I think we're talking about different things here.
> >>  >
> >>  > A mode for automatic bitpool is needed and will have to be the default.
> >>  > XQ bitpool values need to be disabled by default. An option for
> >>  > enabling XQ bitpool values in the automatic mode would be useful, so I
> >>  > hope we will have that.
> >>  >
> >>  > When I said that "the module argument will become obsolete" didn't mean
> >>  > that the XQ option itself would become obsolete. If the option can be
> >>  > configured at run-time, for example with "pactl enable-sbc-xq true" or
> >>  > with pavucontrol, then that will not be implemented via a module
> >>  > argument. It will be implemented using the message API (which is still
> >>  > under review), and the option value will be stored in a database.
> >>  > Having a module argument doesn't add any value in this scheme, which is
> >>  > why I said the module argument will become obsolete.
> >>  >
> >>  > This depends on someone actually implementing the interface for setting
> >>  > the XQ option, however. I hope someone will promise to do that. It
> >>  > could be you, or it could be Pali. I'm not promising to do it myself.
> >>  > If nobody promises to implement that, then I'm going to accept a module
> >>  > argument, because having something is better than having nothing.
> >
> > I have already implemented it! It is in my patch series. Currently
> > selection is done by choosing PA profile (because there is no other
> > mechanism yet).
> >
> >>  It's not obvious to get details of the A2DP protocol without reading the RFC,
> >>  so I'm going to give a few tracks :
> >>
> >>  - Bluetooth packet size is not constant : BT traffic is splited in radio slots
> >>  that have fixed time lengh : so for a given bandwidth : slots size vary
> >
> > Plus there is retransmission at low bluetooth layer when they are lost.
> >
> > Also radio slots are shared across all bluetooth traffic between host
> > and device. So not only A2DP packets are transmitted, but also other
> > packets, like established HSP / HFP or anything else.
> >
> >>  - Bitpool is dynamically reduced when the bandwidth decrease : for example
> >>  when the emitter go away from the receiver.
> >>  - Bitrate is related to bitpool but depends on other parameters (see the attached sheet)
> >>  - Bluetooth A2DP emiters (SRC) usually specify a maximum value for Bitpool.
> >
> > It specify both minimum and maximum (range)
> >
> >>  This value is not the value that will be negociated but rather a
> >>  highest negociation value.
> >
> > Result of negotiation is bitpool range, which must be continuous subset
> > of intersect of supported range of host and device.
> >
> > And then emitter choose any bitpool value from negotiated range,
> > probably always the highest value from that range.
> >
> >>  - SBC XQ is standard SBC codec operating at high bitrates and thus reaching
> >>  the transparent audio transport quality of AptX (HD) . It can be achieved either
> >>  in STEREO MODE, with bitpool ~ 76, or in DUAL CHANNEL MODE, with bitpool ~ 38
> >>  per channel (simplified)
> >>  - "Legacy automatic" is the barbarous name I gave to the traditional negociated algorithm
> >>  with max bitpool=53 and STEREO MODE prefered to DUAL CHANNEL MODE : it is implemented
> >>  in current PA
> >>  - "XQ automatic" is the barbarous name I gave to the negociated algorithm
> >>  implemented in my patch with max bitpool=38 per channel, and DUAL CHANNEL
> >>  prefered to STEREO MODE (simplified)
> >>  - "Forced XQ" modes are several algorithms implemented by Pali with fixed
> >>  bitpool values : not negociated : if the receiver can do the fixed bitpool it works, else
> >>  it fails (simplified)
> >
> > It is negotiated too. If remote side does not announce that it (may)
> > support "forced XQ" then it is not available for PA.
> >
> >>  Now the "quaity switch" idea :
> >>  The "quaity switch" (aka module param or pactl API call, all good for me) is a way
> >>  to switch between "Legacy automatic" and something else giving better quality.
> >>  The "something else" could be :
> >>  - "XQ automatic" + several "Forced XQ" modes (my latest idea, relies on Pali's code + my code + "quaity switch")
> >>  - "XQ automatic" alone (my former idea, relies on my "simple" patch + "quaity switch")
> >>  - several "Forced XQ" modes alone (Pali's idea, relies on Pali's code +"quaity switch")
> >
> > My proposed API in PA server allows to define any settings or
> > combination for SBC codec. So it would be easy to define any such
> > "SBC profile" with my patches.
> 
> So it's all fine for me. Plus the fact that you implemented the bitpool 
> automatic recovery grow up when bandwidth grow : it's perfect.

No, grow up is not implemented. This is missing and I do not know how to
implement it. Because I do not know how to detect that conditions allows
computer to start sending more A2DP packets.

> I would just suggest to add an automatic XQ profile (inspired from 
> my patch if you want to) and make it default when XQ is available 
> on SNK side. 
> This way we don't have to wait for Bluez to provide codec switching 
> and it allows for a 14.0 PA release at the date already scheduled by Tanu.
> 
> JP 
> 
> >
> >>  Pali : please fix the above in case I did some mistakes
> >>  JP
> >>
> >>  >
> >>  > --
> >>  > Tanu
> >>  >
> >>  > https://www.patreon.com/tanuk
> >>  > https://liberapay.com/tanuk
> >
> > --
> > Pali Rohár
> > pali.rohar at gmail.com

-- 
Pali Rohár
pali.rohar at gmail.com