Bluetooth: btusb: check conditions before enabling USB ALT 3 for WBS

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@iki.fi>
Fixes: e848dbd364ac ("Bluetooth: btusb: Add support USB ALT 3 for WBS")
Tested-by: Michał Kępień <kernel@kempniu.pl>
Tested-by: Jonathan Lampérth <jon@h4n.dev>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
index afd2b1f..e0859f4 100644 (file)
--- a/drivers/bluetooth/btusb.c
+++ b/drivers/bluetooth/btusb.c
@@ -486,6 +486,7 @@ 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;
@@ -1718,16 +1719,20 @@ 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 (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)
@@ -4170,6 +4175,7 @@ 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)