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Date:   Wed, 04 Dec 2019 20:45:23 +0530
From:   "Arun Raghavan" <arun@arunraghavan.net>
To:     =?UTF-8?Q?Pali_Roh=C3=A1r?= <pali.rohar@gmail.com>,
        "Tanu Kaskinen" <tanuk@iki.fi>
Cc:     "PulseAudio Discussion" <pulseaudio-discuss@lists.freedesktop.org>,
        linux-bluetooth@vger.kernel.org, ofono@ofono.org,
        devkit-devel@lists.freedesktop.org,
        "Bastien Nocera" <hadess@hadess.net>,
        "Georg Chini" <georg@chini.tk>,
        "Russell Treleaven" <rtreleaven@bunnykick.ca>,
        "Luiz Augusto von Dentz" <luiz.dentz@gmail.com>,
        "Marcel Holtmann" <marcel@holtmann.org>,
        "Sebastian Reichel" <sre@ring0.de>, "Pavel Machek" <pavel@ucw.cz>,
        "Wim Taymans" <wim.taymans@gmail.com>,
        "George Kiagiadakis" <george.kiagiadakis@collabora.com>
Subject: =?UTF-8?Q?Re:_[pulseaudio-discuss]_Proposal_for_a_new_API_and_usage_of_B?=
 =?UTF-8?Q?luetooth_HSP_and_HFP_profiles_on_Linux?=
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Sender: linux-bluetooth-owner@vger.kernel.org
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+Wim and George from PipeWire

On Tue, 3 Dec 2019, at 12:15 AM, Pali Roh=C3=A1r wrote:
> On Monday 02 December 2019 19:01:11 Tanu Kaskinen wrote:
> > On Sun, 2019-12-01 at 19:57 +0100, Pali Roh=C3=A1r wrote:
> > > Hello!
> > >=20
> > > I'm sending this email to relevant mailing lists and other people =
who
> > > could be interested in it. (I'm not subscribed to all of ML, so pl=
ease
> > > CC me when replying).
> > >=20
> > >=20
> > > I would like to open a discussion about a completely new way of ha=
ndling
> > > Bluetooth HSP and HFP profiles on Linux. These two profiles are th=
e only
> > > standard way how to access microphone data from Bluetooth Headsets=
.
> > >=20
> > >=20
> > > Previously in bluez4, HFP profile was implemented by bluez daemon =
and
> > > telephony HFP functionality was provided by either dummy modem, of=
ono
> > > modem or by Nokia's CSD Maemo modem.
> > >=20
> > > In bluez5 version was modem code together with implementation of H=
FP
> > > profile removed. And let implementation of HSP and HFP profiles to=

> > > external application.
> > >=20
> > > Currently HSP profile is implemented in pulseaudio daemon to handl=
e
> > > microphone and Bluetooth speakers. HFP profile is not implemented =
yet.
> > >=20
> > >=20
> > > HSP and HFP profiles use AT modem commands, so its implementation =
needs
> > > to parse and generates AT commands, plus implement needed state ma=
chine
> > > for it.
> > >=20
> > > And now problem is that last version of HFP profile specification =
is too
> > > complicated, plus Bluetooth headsets vendors started to inventing =
and
> > > using of own custom extensions to HFP profile and AT commands.
> > >=20
> > > Main problem of this "external" implementation outside of bluez is=
 that
> > > only one application can communicate with remote Bluetooth device.=
 It
> > > is application which received needed socket from bluez.
> > >=20
> > > So in this design if audio daemon (pulseaudio) implements HFP prof=
ile
> > > for processing audio, and e.g. power supply application wants to
> > > retrieve battery level from Bluetooth device, it means that audio =
daemon
> > > needs to implement also battery related functionality.
> > >=20
> > > It does not make sense to force power supply daemon (upower) to
> > > implement audio routing/encoding/decoding or audio daemon (power s=
upply)
> > > to force implementing battery related operations.
> > >=20
> > >=20
> > > For handle this problem I would like to propose a new way how to u=
se and
> > > implement HSP and HFP profiles on Linux.
> > >=20
> > > Implement a new HSP/HFP daemon (I called it hsphfpd) which registe=
r HSP
> > > and HFP profiles in bluez and then exports functionality for all o=
ther
> > > specific applications via DBus API (API for audio, power supply, i=
nput
> > > layer, telephony functions, vendor extensions, etc...). So it woul=
d acts
> > > as proxy daemon between bluez and target applications (pulseaudio,=

> > > upower, ofono, ...)
> > >=20
> > > This would simplify whole HFP usage as applications would not need=
 to
> > > re-implement parsing and processing of AT commands and it would al=
low
> > > more applications to use HFP profile at one time. And also it mean=
s that
> > > audio software does not have to implement telephony stack or power=

> > > supply operations.
> > >=20
> > >=20
> > > I wrote a document how such DBus API could look like, see here:
> > >=20
> > >   https://github.com/pali/hsphfpd-prototype/raw/prototype/hsphfpd.=
txt
> > >=20
> > >=20
> > > And also I implemented "prototype" implementation to verify that
> > > designed API make sense and can be really implemented. Prototype f=
ully
> > > supports HSP profile in both HS and AG role, plus HFP profile in H=
F
> > > role. This prototype implementation is available here:
> > >=20
> > >   https://github.com/pali/hsphfpd-prototype
> > >=20
> > > Some other details are written in README:
> > >=20
> > >   https://github.com/pali/hsphfpd-prototype/raw/prototype/README
> > >=20
> > >=20
> > > What do you think about it? Does it make sense to have such design=
?
> > > Would you accept usage of such hsphfpd daemon, implemented accordi=
ng to
> > > specification, on Linux desktop?
> > >=20
> > > I would like to hear your opinion if I should continue with this h=
sphfpd
> > > design, or not.
> > >=20
> > >=20
> > > With this design and implementation of hsphfpd is possible to easi=
ly fix
> > > pulseaudio issue about power supply properties:
> > >=20
> > >   https://gitlab.freedesktop.org/pulseaudio/pulseaudio/issues/722
> >=20
> > I quite like this proposal. Avoiding the need to implement the butto=
n
> > press, battery level etc. handling separately in PulseAudio, oFono a=
nd
> > PipeWire seems like a pretty good justification to me. I assume you'=
re
> > volunteering to maintain this new daemon?
>=20
> Yes, I can maintain this new daemon.
>=20
> > It's not clear to me how this would affect the PulseAudio <-> oFono
> > interaction, if at all.
>=20
> Only one application can register to bluez and "own" bluez socket for
> communication with bluetooth headset. Currently it can be either
> pulseaudio (with native backend in pulseaudio for HSP profile) or ofon=
o
> (with ofono backend in pulseaudio for HFP profile).
>=20
> So if hsphfpd would be in use, then ofono would not be able to get
> socket from bluez. And it would be needed to add a new "plugin" into
> ofono to use hsphpfd for telephony operations. See hsphfpd.txt file
> (there is diagram of usage).
>=20
> > When oFono is used, would PulseAudio get the
> > audio socket from oFono or hsphfpd?
>=20
> Always from hsphfpd.
>=20
> > What about volume commands, would they go through oFono or would
> > PulseAudio interact with hsphfpd directly?
>=20
> Internally they are handled by hsphpfd directly and appropriate API is=

> exported via DBus for audio application daemon (pulseaudio). For detai=
ls
> see hsphfpd.txt file, interface org.hsphfpd.AudioTransport.
>=20
> > I think hsphfpd should be part of bluetoothd, but if that's not
> > possible, then that's not possible.
>=20
> I do not know if bluez developers are interested in having this code a=
s
> part of bluez project, specially when in bluez4 HFP profile was there
> and in bluez5 was HFP code completely removed.
>=20
> But it should not matter where hsphpfd is implemented.
>=20
> > (I don't want to get into a lengthy discussion about programming
> > languages, but I'll just note here that I don't like Perl.)
>=20
> It is just a prototype. I used Perl just because it is faster for me t=
o
> implement parsing of AT commands needed for prototype purposes.

Broadly, I think this is a good thing to do. My main concern is having t=
his be adequately maintained over a longer period of time.

The other thing to note is that in PipeWire, it is possible for external=
 entities to implement the equivalent of a "sink" or "source" (it's just=
 a node in PipeWire terminology), so in the long run, it might be good t=
o have a single BT audio daemon that manages A2DP and HSP/HFP..

This would also have the benefit of moving codec dependencies out of Pul=
seAudio (which I'll help mitigate in other ways within PulseAudio anyway=
).

Cheers,
Arun