[PATCH 1/2] Bluetooth: btmtk: Fix btmtk_usb_subsys_reset() reporting success on failure

[Ismail Tarim]

btmtk_usb_subsys_reset() validates the subsystem reset by reading the
chip id back. When that read succeeds at the bus level but yields an id
of zero, the reset has demonstrably not taken effect: the function logs
"Can't get device id, subsys reset fail." and then returns the return
value of btmtk_usb_id_get(), which in that case is zero, i.e. success.

btusb_mtk_reset() returns that value unchanged, so its caller cannot
tell a completed reset from a failed one.

Return -ENODEV when the chip id reads back as zero, leaving the existing
MT6639 exemption intact.

Observed on an MT7902 [13d3:3579] where the controller firmware asserts
and the subsequent subsystem reset fails, yet the driver continues as if
the reset had succeeded:

  Bluetooth: hci0: Mediatek coredump end
  Bluetooth: hci0: Can't get device id, subsys reset fail.
  usb 3-10: reset high-speed USB device number 5 using xhci_hcd
  usb 3-10: device descriptor read/64, error -110
  usb usb3-port10: attempt power cycle
  usb usb3-port10: unable to enumerate USB device

Note that this corrects the error reporting only; it does not by itself
make the controller recoverable in the case above.

Fixes: 25b6d7593a3a ("Bluetooth: btmtk: introduce btmtk reset work")
Signed-off-by: Ismail Tarim <ismailtarim7 at gmail.com>
---
 drivers/bluetooth/btmtk.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/bluetooth/btmtk.c b/drivers/bluetooth/btmtk.c
index 66b346761043..dc702c0a6034 100644
--- a/drivers/bluetooth/btmtk.c
+++ b/drivers/bluetooth/btmtk.c
@@ -968,8 +968,10 @@ int btmtk_usb_subsys_reset(struct hci_dev *hdev, u32 dev_id)
 	}
 
 	err = btmtk_usb_id_get(hdev, 0x70010200, &val);
-	if (err || (!val && dev_id != 0x6639))
+	if (err || (!val && dev_id != 0x6639)) {
 		bt_dev_err(hdev, "Can't get device id, subsys reset fail.");
+		return err ? err : -ENODEV;
+	}
 
 	return err;
 }
-- 
2.55.0