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Date:   Sun, 19 May 2019 14:22:23 +0200
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali.rohar@gmail.com>
To:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     linux-bluetooth@vger.kernel.org
Subject: Re: bluez A2DP socket reliability
Message-ID: <20190519122223.gabew7qfftihlbic@pali>
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On Sunday 19 May 2019 11:13:09 Luiz Augusto von Dentz wrote:
> Hi Pali,
>=20
> On Sat, May 18, 2019 at 11:12 PM Pali Roh=C3=A1r <pali.rohar@gmail.com> w=
rote:
> >
> > Hello! How is L2CAP layer of bluetooth socket used for A2DP audio
> > transfer configured in bluez? It is reliable with big/infinite
> > retransmit count? Or in best-effort manner and some packets may be
> > dropped? And it is possible to change between these two modes for
> > application which uses bluez DBUS API? I'm asking because some A2DP
> > audio codecs are designed to deal with packet loss and for those codecs
> > it would be probably better to configure L2CAP socket to unreliable
> > mode.
>=20
> We don't use ERTM with AVDTP, both signaling and transport sockets are
> using basic mode which don't support retransmissions, there the
> concept of flush timeout which iirc we don't currently it.

On bluez.org site there is no information how to use bluez sockets and
the only documentation/tutorial which I found on internet was this:

  https://people.csail.mit.edu/albert/bluez-intro/x559.html

I do not know how up-to-date it is, but seems that by default bluez
L2CAP sockets are reliable and to change them to unreliable mode it is
needed to issue OGF_HOST_CTL / OCF_WRITE_AUTOMATIC_FLUSH_TIMEOUT (0x28)
request. As default is zero =3D infinity =3D reliable connection.

I do not understand low level bluetooth details, but is ERTM related to
OCF_WRITE_AUTOMATIC_FLUSH_TIMEOUT?

So what are default settings for L2CAP socket used by AVDTP/A2DP
profiles which are transferred to user application via DBUS?

--=20
Pali Roh=C3=A1r
pali.rohar@gmail.com

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