drivers/tty: 8250: only call fintek_8250_probe when doing port I/O

commit 4c4fc909 upstream.

Commit fa01e2ca ("serial: 8250: Integrate Fintek into 8250_base")
modified the probing logic for PNP0501 devices, to remove a collision
between the generic 16550A driver and the Fintek driver, which reused
the same ACPI _HID.

The Fintek device probe is now incorporated into the common 8250 probe
path, and gets called for all discovered 16550A compatible devices,
including ones that are MMIO mapped rather than IO mapped. However,
the Fintek driver assumes the port base is a I/O address, and proceeds
to probe some arbitrary offsets above it.

This is generally a wrong thing to do, but on ARM systems (having no
native port I/O), this may result in faulting accesses of completely
unrelated MMIO regions in the PCI I/O space. Given that this is at
serial probe time, this results in hard to diagnose crashes at boot.

So let's restrict the Fintek probe to devices that we know are using
port I/O in the first place.

Fixes: fa01e2ca ("serial: 8250: Integrate Fintek into 8250_base")
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Ricardo Ribalda <ricardo.ribalda@gmail.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_port.c

@@ -1337,7 +1337,7 @@ static void autoconfig(struct uart_8250_port *up)
 	/*
 	 * Check if the device is a Fintek F81216A
 	 */
-	if (port->type == PORT_16550A)
+	if (port->type == PORT_16550A && port->iotype == UPIO_PORT)
 		fintek_8250_probe(up);
 
 	if (up->capabilities != old_capabilities) {