[+cc stable@vger.kernel.org]

Hi,

On Sat, Feb 06, 2021 at 04:56:53PM +0100, Sjoerd Simons wrote:

On Fri, Dec 18, 2020 at 10:23:08PM +0100, Marcel Holtmann wrote:

...

Hi Trent,

...

When alt mode 6 is not available, fallback to the kernel <= 5.7 behavior of always using alt mode 1.

Prior to kernel 5.8, btusb would always use alt mode 1 for WBS (Wide Band Speech aka mSBC aka transparent SCO). In commit baac6276c0a9 ("Bluetooth: btusb: handle mSBC audio over USB Endpoints") this was changed to use alt mode 6, which is the recommended mode in the Bluetooth spec (Specifications of the Bluetooth System, v5.0, Vol 4.B §2.2.1). However, many if not most BT USB adapters do not support alt mode 6. In fact, I have been unable to find any which do.

...

patch has been applied to bluetooth-next tree.

For easier application to the stable tree(s) this should probably get: Fixes: baac6276c0a9 ("Bluetooth: btusb: handle mSBC audio over USB Endpoints")

In my testing this indeed fixes mSBC audio with both a Belkin (Broadcom BCM20702A, 050d:065a) and an Intel Bluetooth (8087:0a2b) adapters.

Tested-By: Sjoerd Simons sjoerd@collabora.com

Tested on Intel AX200 Bluetooth (8087:0029):

Tested-by: Sebastian Reichel sre@kernel.org

The patch has been merged to Linus' tree today and I think it should be applied to the 5.10 tree, which is used by Debian. This patch is required to use BT headset with bidirectional-audio in acceptable quality (That also requires proper userspace software, e.g. pipewire 0.3.22, which Sjoerd uploaded to Debian experimental).

Patch applies cleanly on 5.10.

Thanks,

-- Sebastian