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From:   Emil Lenngren <emil.lenngren@gmail.com>
Date:   Wed, 4 Mar 2020 22:40:51 +0000
Message-ID: <CAO1O6sfp2ikCkAY3UGvxe-+F-L-nG=cdTqjzthrv4ddrADxWnw@mail.gmail.com>
Subject: Re: Get negotiated ATT MTU?
To:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     Jamie Mccrae <Jamie.Mccrae@lairdconnect.com>,
        Bluez mailing list <linux-bluetooth@vger.kernel.org>
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Hi Luiz,

Den ons 4 mars 2020 kl 20:44 skrev Luiz Augusto von Dentz
<luiz.dentz@gmail.com>:
> > > It completely transparent to D-Bus, so if we do expose the MTU it
> > > should probably be reporting the biggest MTU of all connected channel,
> >
> > Is there ever any reason for one application to have more than one ATT
> > bearer? I thought the idea of EATT was to allow one ATT bearer per
> > application.
>
> EATT is meant to allow multiple outstanding requests, it probably
> would not escale if we would add an API to have a bearer per
> application so we just use the extra bearers as a pool.

I just read the 5.2 overview and 5.2 specification again and I see now
that the overview suggests that a pool of bearers should be used, as
you mentioned. So yes in that case the maximum ATT_MTU of the bearers
seems reasonable to report (if they for some reason would differ). But
by having a pool like this, I hope implementations will make sure that
multiple Write Without Response values or notifications from the same
application are sent on a single bearer, to avoid reorderings.

/Emil