PCI/MSI: Allow msi_domain lookup using the host bridge node

A number of platforms do not need to use the msi-parent property,
as the host bridge itself provides the MSI controller.

Allow this configuration by performing an irq domain lookup based
on the host bridge node if it doesn't have a valid msi-parent property.
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: <linux-arm-kernel@lists.infradead.org>
Cc: Yijing Wang <wangyijing@huawei.com>
Cc: Ma Jun <majun258@huawei.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Duc Dang <dhdang@apm.com>
Cc: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1438091186-10244-7-git-send-email-marc.zyngier@arm.comSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/pci/of.c

@@ -72,8 +72,13 @@ struct irq_domain *pci_host_bridge_of_msi_domain(struct pci_bus *bus)
 
 	/* Start looking for a phandle to an MSI controller. */
 	np = of_parse_phandle(bus->dev.of_node, "msi-parent", 0);
+
+	/*
+	 * If we don't have an msi-parent property, look for a domain
+	 * directly attached to the host bridge.
+	 */
 	if (!np)
-		return NULL;
+		np = bus->dev.of_node;
 
 	d = irq_find_matching_host(np, DOMAIN_BUS_PCI_MSI);
 	if (d)