Re: [PATCH] Bluetooth: btusb: check SCO MTU before enabling USB ALT 3 for WBS

["Pasi Kärkkäinen" <pasik@iki.fi>]

Hi Pauli,

On Fri, Jul 16, 2021 at 08:58:17PM +0300, Pauli Virtanen wrote:
> Some USB BT adapters don't satisfy the MTU requirement mentioned in
> commit e848dbd364ac ("Bluetooth: btusb: Add support USB ALT 3 for WBS")
> and have ALT 3 setting that produces no/garbled audio. Check that the MTU
> condition is satisfied, and fall back to ALT 1 if not.
> 
> Tested with USB adapters (mtu<72, produce sound only with ALT1)
> BCM20702A1 0b05:17cb, CSR8510A10 0a12:0001, and (mtu>=72, ALT3)
> RTL8761BU 0bda:8771, Intel AX200 8087:0029 (after disabling ALT6).
> 
> Signed-off-by: Pauli Virtanen <pav@iki.fi>
> ---
>

Maybe add a Fixes: tag ?


Thanks,

-- Pasi

>  drivers/bluetooth/btusb.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> index a9855a2dd561..3ee66e415c4d 100644
> --- a/drivers/bluetooth/btusb.c
> +++ b/drivers/bluetooth/btusb.c
> @@ -1763,9 +1763,11 @@ static void btusb_work(struct work_struct *work)
>  			/* Because mSBC frames do not need to be aligned to the
>  			 * SCO packet boundary. If support the Alt 3, use the
>  			 * Alt 3 for HCI payload >= 60 Bytes let air packet
> -			 * data satisfy 60 bytes.
> +			 * data satisfy 60 bytes. USB Alt 3 support also needs
> +			 * HFP transparent MTU >= 72 Bytes.
>  			 */
> -			if (new_alts == 1 && btusb_find_altsetting(data, 3))
> +			if (new_alts == 1 && hdev->sco_mtu >= 72 &&
> +			    btusb_find_altsetting(data, 3))
>  				new_alts = 3;
>  		}
>  
> -- 
> 2.31.1
> 
>