From: Trent Piepho tpiepho@gmail.com
commit 517b693351a2d04f3af1fc0e506ac7e1346094de upstream.
When alt mode 6 is not available, fallback to the kernel <= 5.7 behavior of always using alt mode 1.
Prior to kernel 5.8, btusb would always use alt mode 1 for WBS (Wide Band Speech aka mSBC aka transparent SCO). In commit baac6276c0a9 ("Bluetooth: btusb: handle mSBC audio over USB Endpoints") this was changed to use alt mode 6, which is the recommended mode in the Bluetooth spec (Specifications of the Bluetooth System, v5.0, Vol 4.B ยง2.2.1). However, many if not most BT USB adapters do not support alt mode 6. In fact, I have been unable to find any which do.
In kernel 5.8, this was changed to use alt mode 6, and if not available, use alt mode 0. But mode 0 has a zero byte max packet length and can not possibly work. It is just there as a zero-bandwidth dummy mode to work around a USB flaw that would prevent device enumeration if insufficient bandwidth were available for the lowest isoc mode supported.
In effect, WBS was broken for all USB-BT adapters that do not support alt 6, which appears to nearly all of them.
Then in commit 461f95f04f19 ("Bluetooth: btusb: USB alternate setting 1 for WBS") the 5.7 behavior was restored, but only for Realtek adapters.
I've tested a Broadcom BRCM20702A and CSR 8510 adapter, both work with the 5.7 behavior and do not with the 5.8.
So get rid of the Realtek specific flag and use the 5.7 behavior for all adapters as a fallback when alt 6 is not available. This was the kernel's behavior prior to 5.8 and I can find no adapters for which it is not correct. And even if there is an adapter for which this does not work, the current behavior would be to fall back to alt 0, which can not possibly work either, and so is no better.
Signed-off-by: Trent Piepho tpiepho@gmail.com Signed-off-by: Marcel Holtmann marcel@holtmann.org Cc: Salvatore Bonaccorso carnil@debian.org Cc: Sjoerd Simons sjoerd@luon.net Cc: Sebastian Reichel sre@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/bluetooth/btusb.c | 20 ++++++-------------- 1 file changed, 6 insertions(+), 14 deletions(-)
--- a/drivers/bluetooth/btusb.c +++ b/drivers/bluetooth/btusb.c @@ -506,7 +506,6 @@ static const struct dmi_system_id btusb_ #define BTUSB_HW_RESET_ACTIVE 12 #define BTUSB_TX_WAIT_VND_EVT 13 #define BTUSB_WAKEUP_DISABLE 14 -#define BTUSB_USE_ALT1_FOR_WBS 15
struct btusb_data { struct hci_dev *hdev; @@ -1736,15 +1735,12 @@ static void btusb_work(struct work_struc new_alts = data->sco_num; } } else if (data->air_mode == HCI_NOTIFY_ENABLE_SCO_TRANSP) { - /* Check if Alt 6 is supported for Transparent audio */ - if (btusb_find_altsetting(data, 6)) { - data->usb_alt6_packet_flow = true; - new_alts = 6; - } else if (test_bit(BTUSB_USE_ALT1_FOR_WBS, &data->flags)) { - new_alts = 1; - } else { - bt_dev_err(hdev, "Device does not support ALT setting 6"); - } + /* 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. + */ + new_alts = btusb_find_altsetting(data, 6) ? 6 : 1; }
if (btusb_switch_alt_setting(hdev, new_alts) < 0) @@ -4548,10 +4544,6 @@ static int btusb_probe(struct usb_interf * (DEVICE_REMOTE_WAKEUP) */ set_bit(BTUSB_WAKEUP_DISABLE, &data->flags); - if (btusb_find_altsetting(data, 1)) - set_bit(BTUSB_USE_ALT1_FOR_WBS, &data->flags); - else - bt_dev_err(hdev, "Device does not support ALT setting 1"); }
if (!reset)