usb: musb: fix setting JZ4740 gadget periphal mode on reset

JZ4740 USB Device Controller is not OTG compatible and does not have
DEVCTL register in silicon.

During ethernet-over-usb transactions, on reset, musb driver tries to
read from DEVCTL and consequently sets device as host (A-Device)
instead of peripheral (B-Device), which makes it a composite device to
the USB gadget driver.
This induces a kernel panic during power down where the USB gadget
driver does a null pointer dereference when trying to access the
composite device configuration.

On reset, do not rely on DEVCTL value for setting gadget peripheral
mode. Use is_otg flag instead to set it to B-Device.

Signed-off-by: Apelete Seketeli <apelete@seketeli.net>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_gadget.c

@@ -2119,7 +2119,15 @@ __acquires(musb->lock)
 	/* Normal reset, as B-Device;
 	 * or else after HNP, as A-Device
 	 */
-	if (devctl & MUSB_DEVCTL_BDEVICE) {
+	if (!musb->g.is_otg) {
+		/* USB device controllers that are not OTG compatible
+		 * may not have DEVCTL register in silicon.
+		 * In that case, do not rely on devctl for setting
+		 * peripheral mode.
+		 */
+		musb->xceiv->state = OTG_STATE_B_PERIPHERAL;
+		musb->g.is_a_peripheral = 0;
+	} else if (devctl & MUSB_DEVCTL_BDEVICE) {
 		musb->xceiv->state = OTG_STATE_B_PERIPHERAL;
 		musb->g.is_a_peripheral = 0;
 	} else {