Re: [PATCH v2] Bluetooth: btusb: check conditions before enabling USB ALT 3 for WBS

[Marcel Holtmann <marcel@holtmann.org>]

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@iki.fi>
> 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