powerpc/pmac: Fix internal modem IRQ on Wallstreet PowerBook

The (relatively) new pmac_zilog driver doesn't use the pre-munged
IRQ numbers from the macio_dev unlike other macio things, it
directly maps it off the OF device-tree.

It does that because it can be initialized much earlier than the
registration of the macio devices, in order to get a serial
console early.

Unfortunately, that means that it "misses" some fixups done
by the macio layer to work around missing interrupt descriptions
in the device-tree of the Wallstreet machines.

This patch brings the necessary workaround into the pmac_zilog
driver itself to bring it back to working condition.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

drivers/serial/pmac_zilog.c

@@ -1538,6 +1538,21 @@ static int __init pmz_init_port(struct uart_pmac_port *uap)
 	uap->port.type = PORT_PMAC_ZILOG;
 	uap->port.flags = 0;
 
+	/*
+	 * Fixup for the port on Gatwick for which the device-tree has
+	 * missing interrupts. Normally, the macio_dev would contain
+	 * fixed up interrupt info, but we use the device-tree directly
+	 * here due to early probing so we need the fixup too.
+	 */
+	if (uap->port.irq == NO_IRQ &&
+	    np->parent && np->parent->parent &&
+	    of_device_is_compatible(np->parent->parent, "gatwick")) {
+		/* IRQs on gatwick are offset by 64 */
+		uap->port.irq = irq_create_mapping(NULL, 64 + 15);
+		uap->tx_dma_irq = irq_create_mapping(NULL, 64 + 4);
+		uap->rx_dma_irq = irq_create_mapping(NULL, 64 + 5);
+	}
+
 	/* Setup some valid baud rate information in the register
 	 * shadows so we don't write crap there before baud rate is
 	 * first initialized.