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

[Joseph Hwang <josephsih@google.com>]

It looks reasonable to check sco_mtu. My suggestion is to use
hci_packet_size_usb_alt[3] instead of the magic number 72.

Thanks,
Joseph


On Sat, Jul 17, 2021 at 1:58 AM Pauli Virtanen <pav@iki.fi> 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>
> ---
>  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
>
>


-- 

Joseph Shyh-In Hwang
Email: josephsih@google.com