[PATCH 5.14 02/11] Bluetooth: btusb: check conditions before enabling USB ALT 3 for WBS

[Greg Kroah-Hartman]

From: Pauli Virtanen <pav@xxxxxx>

commit 55981d3541812234e687062926ff199c83f79a39 upstream.

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")
Tested-by: Michał Kępień <kernel@xxxxxxxxxx>
Tested-by: Jonathan Lampérth <jon@xxxxxxx>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/bluetooth/btusb.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--- a/drivers/bluetooth/btusb.c
+++ b/drivers/bluetooth/btusb.c
@@ -525,6 +525,7 @@ 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_ALT3_FOR_WBS	15
 
 struct btusb_data {
 	struct hci_dev       *hdev;
@@ -1757,16 +1758,20 @@ static void btusb_work(struct work_struc
 			/* 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 (btusb_find_altsetting(data, 3) &&
+				 hdev->sco_mtu >= 72 &&
+				 test_bit(BTUSB_USE_ALT3_FOR_WBS, &data->flags))
 				new_alts = 3;
+			else
+				new_alts = 1;
 		}
 
 		if (btusb_switch_alt_setting(hdev, new_alts) < 0)
@@ -4742,6 +4747,7 @@ static int btusb_probe(struct usb_interf
 		 * (DEVICE_REMOTE_WAKEUP)
 		 */
 		set_bit(BTUSB_WAKEUP_DISABLE, &data->flags);
+		set_bit(BTUSB_USE_ALT3_FOR_WBS, &data->flags);
 	}
 
 	if (!reset)