Hi Pauli,
> 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. Some adapters
> with larger MTU were also reported to have problems with ALT 3.
>
> Add a flag and check it and MTU before selecting ALT 3, falling back to
> ALT 1. Enable the flag for Realtek, restoring the previous behavior for
> non-Realtek devices.
>
> Tested with USB adapters (mtu<72, no/garbled sound with ALT3, ALT1
> works) BCM20702A1 0b05:17cb, CSR8510A10 0a12:0001, and (mtu>=72, ALT3
> works) RTL8761BU 0bda:8771, Intel AX200 8087:0029 (after disabling
> ALT6). Also got reports for (mtu>=72, ALT 3 reported to produce bad
> audio) Intel 8087:0a2b.
>
> Signed-off-by: Pauli Virtanen <pav@xxxxxx>
> Fixes: e848dbd364ac ("Bluetooth: btusb: Add support USB ALT 3 for WBS")
before I will apply this, I need Tested-by or Ack-by people that confirm that this fixes their issues now.
> ---
>
> Changes in v2:
> - Explain magic number 72 in a comment; didn't add the table for them,
> because it's not used elsewhere and we need just one number from it.
> - Add flag for ALT3 support, restoring the behavior
> for non-Realtek devices the same as before e848dbd364ac, due to
> the problems reported on an Intel adapter. Don't have the device
> myself.
>
> drivers/bluetooth/btusb.c | 22 ++++++++++++++--------
> 1 file changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> index 6d23308119d1..5cec719f6cba 100644
> --- a/drivers/bluetooth/btusb.c
> +++ b/drivers/bluetooth/btusb.c
> @@ -516,6 +516,7 @@ static const struct dmi_system_id btusb_needs_reset_resume_table[] = {
> #define BTUSB_HW_RESET_ACTIVE 12
> #define BTUSB_TX_WAIT_VND_EVT 13
> #define BTUSB_WAKEUP_DISABLE 14
> +#define BTUSB_ALT3_OK_FOR_WBS 15
Rename this to BTUSB_USE_ALT3_FOR_WBS.
>
> struct btusb_data {
> struct hci_dev *hdev;
> @@ -1748,16 +1749,20 @@ static void btusb_work(struct work_struct *work)
> /* Bluetooth USB spec recommends alt 6 (63 bytes), but
> * many adapters do not support it. Alt 1 appears to
> * work for all adapters that do not have alt 6, and
> - * which work with WBS at all.
> + * which work with WBS at all. Some devices prefer
> + * alt 3 (HCI payload >= 60 Bytes let air packet
> + * data satisfy 60 bytes), requiring
> + * MTU >= 3 (packets) * 25 (size) - 3 (headers) = 72
> + * see also Core spec 5, vol 4, B 2.1.1 & Table 2.1.
> */
> - new_alts = btusb_find_altsetting(data, 6) ? 6 : 1;
> - /* 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.
> - */
> - if (new_alts == 1 && btusb_find_altsetting(data, 3))
> + if (btusb_find_altsetting(data, 6))
> + new_alts = 6;
> + else if (test_bit(BTUSB_ALT3_OK_FOR_WBS, &data->flags) &&
> + hdev->sco_mtu >= 72 &&
> + btusb_find_altsetting(data, 3))
This is whitespace damaged.
> new_alts = 3;
> + else
> + new_alts = 1;
> }
>
> if (btusb_switch_alt_setting(hdev, new_alts) < 0)
> @@ -4733,6 +4738,7 @@ static int btusb_probe(struct usb_interface *intf,
> * (DEVICE_REMOTE_WAKEUP)
> */
> set_bit(BTUSB_WAKEUP_DISABLE, &data->flags);
> + set_bit(BTUSB_ALT3_OK_FOR_WBS, &data->flags);
> }
Regards
Marcel
