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Date:   Fri, 7 Jun 2019 15:00:21 +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
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On Sunday 19 May 2019 14:22:23 Pali Rohár wrote:
> On Sunday 19 May 2019 11:13:09 Luiz Augusto von Dentz wrote:
> > Hi Pali,
> > 
> > On Sat, May 18, 2019 at 11:12 PM Pali Rohár <pali.rohar@gmail.com> wrote:
> > >
> > > 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.
> > 
> > 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 = infinity = 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?

Hi! Do you have any idea about OCF_WRITE_AUTOMATIC_FLUSH_TIMEOUT? It is
related to ERTM or not?

-- 
Pali Rohár
pali.rohar@gmail.com