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

Hi Pasi, Pauli,

On Tue, Aug 10, 2021 at 9:50 AM Pasi Kärkkäinen [off-list ref] wrote:

Hello Marcel,

On Fri, Jul 23, 2021 at 02:19:09PM +0200, Marcel Holtmann wrote:

quoted

Hi Pauli,

quoted

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 <redacted>
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.

Is v3 ok/enough? It has one Tested-by.
It would probably be good to send v4 anyway with CC stable@kernel.org ..


Thanks,

-- Pasi

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quoted

---

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.

quoted

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.

Ive fixed this and made it fit in 80 columns by reordering the checks.

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                            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

Applied, thanks.


-- 
Luiz Augusto von Dentz