[PATCH v5 2/8] Bluetooth: btmtk: fix ISO interface setup for single alt setting

Javier Tia
2026-03-31T17:09:53Z

Some MT6639 Bluetooth USB interfaces (e.g. IMC Networks 13d3:3588 on
ASUS ROG STRIX X870E-E and ProArt X870E-Creator boards) expose only a
single alternate setting (alt 0) on the ISO interface. The driver
unconditionally requests alt setting 1, which fails with EINVAL on
these devices, causing a ~20 second initialization delay and no LE
audio support.

Check the number of available alternate settings before selecting one.
If only alt 0 exists, use it; otherwise request alt 1 as before.

Closes: https://github.com/jetm/mediatek-mt7927-dkms/pull/39
Signed-off-by: Javier Tia <floss@jetm.me>
Reported-by: Ryan Gilbert <xelnaga@gmail.com>
Tested-by: Ryan Gilbert <xelnaga@gmail.com>
---
drivers/bluetooth/btmtk.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/bluetooth/btmtk.c b/drivers/bluetooth/btmtk.c
index 4af19b86c551..f8cff895f14c 100644
--- a/drivers/bluetooth/btmtk.c
+++ b/drivers/bluetooth/btmtk.c
@@ -1029,7 +1029,8 @@ static int __set_mtk_intr_interface(struct hci_dev *hdev)
if (!btmtk_data->isopkt_intf)
return -ENODEV;

- err = usb_set_interface(btmtk_data->udev, MTK_ISO_IFNUM, 1);
+ err = usb_set_interface(btmtk_data->udev, MTK_ISO_IFNUM,
+ (intf->num_altsetting > 1) ? 1 : 0);
if (err < 0) {
bt_dev_err(hdev, "setting interface failed (%d)", -err);
return err;

--
2.53.0