Hi,
Thanks for your supplement.
Add the sco_mtu condition is better.
When USB BT adapters support the alternate 3, it will announce alternate 3.
However, USB Alt 3 supported also need HFP support transparent MTU in 72 Bytes.
Add this sco_mtu condition could avoid HFP profile transparent MTU not match or not suitable ALT 3.
Regards,
Hilda
-----Original Message-----
From: Pauli Virtanen <pav@xxxxxx>
Sent: Wednesday, July 21, 2021 11:40 PM
To: Joseph Hwang <josephsih@xxxxxxxxxx>
Cc: linux-bluetooth <linux-bluetooth@xxxxxxxxxxxxxxx>; Hilda Wu <hildawu@xxxxxxxxxxx>
Subject: Re: [PATCH] Bluetooth: btusb: check SCO MTU before enabling USB ALT 3 for WBS
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@xxxxxx> 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@xxxxxx>
> > ---
> > 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
> >
> >
>
>
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