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Date:   Mon, 21 Dec 2020 22:14:37 +0100
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     Joakim Tjernlund <Joakim.Tjernlund@infinera.com>,
        "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>
Subject: Re: Default to HW mSBC on capable controllers ?
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On Friday 18 December 2020 11:43:32 Luiz Augusto von Dentz wrote:
> Hi Joakim,
> 
> On Fri, Dec 18, 2020 at 10:48 AM Joakim Tjernlund
> <Joakim.Tjernlund@infinera.com> wrote:
> >
> > There seems to be quite a few USB controllers gaining the BTUSB_WIDEBAND_SPEECH which I guess means HW mSBC but currently there is no way to select this mode.
> > Any idea if one could patch the kernel to default to HW mSBC and user apps like bluealsa/pulseaudio would just use it automatically?
> 
> It is in our plan to support HW offloading, but that doesn't mean all
> platforms will be supported since that depends on the PCM lines being
> connected to BT controller in the first place.

Dedicated PCM lines are used in embedded world and maybe also still in
some mobile segment. I remember that e.g. Nokia N900 had this setup. And
it was quite crazy how it was finally configured... but it worked!

But this is nothing for classic x86 laptops with USB bluetooth
controllers on classic intel bluetooth+wifi mPCIe cards where SCO
traffic is routed via HCI (over USB). And not via dedicated PCM pins.
Moreover I think there are not any mainstream laptop which have PCM pins
on mPCIe slots usable for such bluetooth mPCIe cards.

For classic desktop / laptop it is needed to deal with fact that SCO
audio is routed via HCI (like A2DP) and therefore support for Enhanced
Setup Synchronous Connection HCI command.

AFAIK even for routing SCO over PCM when mSBC hw encoder is used,
Enhanced Setup Synchronous Connection HCI command is required.