[PATCH v2 1/2] Bluetooth: btmtk: Do not report success when subsys reset fails

[Ismail Tarim <ismailtarim7@gmail.com>]

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]. The path can be reached on demand by
asking the controller for a coredump, since btmtk requests a reset once
the dump completes:

  # echo 1 > /sys/class/bluetooth/hci0/device/coredump

  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

The same sequence occurs unprompted when the controller firmware asserts
on its own.

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@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