Re: bluez: Export SDP "Remote audio volume control" item for HSP profile

From: "Pali Rohár" <pali.rohar@gmail.com>
To: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc: "linux-bluetooth@vger.kernel.org"
	<linux-bluetooth@vger.kernel.org>,
	David Heidelberg <david@ixit.cz>
Subject: Re: bluez: Export SDP "Remote audio volume control" item for HSP profile
Date: Sat, 21 Mar 2020 19:40:15 +0100	[thread overview]
Message-ID: <20200321184015.mtmb7zfk3jqcf6ya@pali> (raw)
In-Reply-To: <CABBYNZ+nuBOH8gu1EJ4iF_r8v53g3rvVMcCm_Kt=5SXijhQY7A@mail.gmail.com>

On Friday 20 March 2020 10:48:02 Luiz Augusto von Dentz wrote:
> Hi Pali,
> 
> On Fri, Mar 20, 2020 at 6:02 AM Pali Rohár <pali.rohar@gmail.com> wrote:
> >
> > On Sunday 09 February 2020 14:02:43 Pali Rohár wrote:
> > > On Friday 13 December 2019 00:03:14 Pali Rohár wrote:
> > > > On Thursday 12 December 2019 21:42:27 Luiz Augusto von Dentz wrote:
> > > > > Hi Pali,
> > > > >
> > > > > On Thu, Dec 12, 2019 at 7:31 PM Pali Rohár <pali.rohar@gmail.com> wrote:
> > > > > >
> > > > > > Hello!
> > > > > >
> > > > > > According to HSP 1.2 specification, section 4.7 Remote Audio Volume
> > > > > > Control, Support for remote audio volume control is optional, so an
> > > > > > implementation may support none, either, or both of the controls for
> > > > > > microphone volume and speaker volume.
> > > > > >
> > > > > > According to HSP 1.2 specification, section 5.3 SDP Interoperability
> > > > > > Requirements, bluetooth device with HSP profile announce via SDP "Remote
> > > > > > audio volume control" field information if device itself supports volume
> > > > > > control.
> > > > > >
> > > > > > But currently I did not found any way how to access "Remote audio volume
> > > > > > control" SDP field in (pulseaudio) application as bluez does not export
> > > > > > it.
> > > > > >
> > > > > > Can you please export this field? E.g. for HFP profile all optional
> > > > > > features from SDP are passed to NewConnection() DBus method via
> > > > > > fd_properties dictionary under Features key. Could you export that
> > > > > > "Remote audio volume control" bit for HSP profile in Features key?
> > > > > >
> > > > > > And in same way, this needs to be handled also in RegisterProfile() DBus
> > > > > > method.
> > > > >
> > > > > Do you have a use case in mind?
> > > >
> > > > Yes, checking in pulseaudio if remote side announce that supports remote
> > > > volume control or not. And based on this switch to software volume
> > > > level.
> > >
> > > Hello Luiz! Is it is possible to export this field?
> >
> > Hello, I have not got any answer to my question.
> >
> > So may I ask again how to retrieve SDP attribute 0x0302 "Remote audio
> > volume control" for a remote bluetooth headset with HSP profile?
> >
> > It is really important as this attribute says if remote bluetooth
> > headset supports volume control or not. In case it does not support, we
> > need to switch to software volume control on host side.
> >
> > There is open pulseaudio bug that on some headsets it is not possible to
> > control volume level and therefore pulseaudio needs to switch to
> > software volume control.
> >
> > But without checking this SDP attribute 0x0302 this is not possible.
> 
> Not sure when I will have time to work on this one, btw can't you
> actually detect this via some AT command, or the headset simple don't
> respond to the AT command for volume control?

Hello Luiz! I'm planing to add some "workaround" by detecting what
happen when VGS or VGM commands are sent. But this is just a workaround
and I would like to know how would proper solution would like.

Does it mean that currently it is really not possible to retrieve SDP
attributes of remote device? And we need to wait until bluez daemon
exports it via DBus API (fd_properties dictionary under Features key)?

-- 
Pali Rohár
pali.rohar@gmail.com