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>
---
Changes in v3:
- Rename flag to BTUSB_USE_ALT3_FOR_WBS.
- No spaces in indent.
- Added Tested-by: Michał Kępień
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..e8062d0b7d4d 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_USE_ALT3_FOR_WBS 15
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_USE_ALT3_FOR_WBS, &data->flags) &&
+ hdev->sco_mtu >= 72 &&
+ btusb_find_altsetting(data, 3))
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_USE_ALT3_FOR_WBS, &data->flags);
}
if (!reset)
--
2.31.1
