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

[Pauli Virtanen <pav@iki.fi>]

Hi,

la, 2021-07-17 kello 21:34 +0800, Joseph Hwang kirjoitti:
> 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 for looking at it. IIUC, hci_packet_size_usb_alt only appears in
previous discussions on this list, which did not seem to reach a
conclusion if this should be computed from wMaxPacketSize. I can do
less magical v2 and add the table.

Different solution would be to make the altsetting choice
manufacturer/device specific flag, as I'm not sure on what hardware
e848dbd364ac was tested on, so maybe it is intended Realtek specific.

Best,
Pauli


> 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
> > 
> > 
> 
>