PCI/MSI: Fix MSIs for generic hosts that use device-tree's "msi-map"

Since commit 9ec37ef ("PCI/MSI: Make pci_host_common_probe() declare
its reliance on MSI domains"), platforms that rely on the "msi-map"
device-tree property don't get MSIs anymore.

On the Arm Fast Model for example [1], the host bridge doesn't have a
"msi-parent" property since it doesn't itself generate MSIs, and so doesn't
get a MSI domain. It has an "msi-map" property instead to describe MSI
controllers of child devices. As a result, due to the new msi_domain check
in pci_register_host_bridge(), the whole bus gets PCI_BUS_FLAGS_NO_MSI.

Check whether the root complex has an "msi-map" property before giving
up on MSIs.

[1] arch/arm64/boot/dts/arm/fvp-base-revc.dts

Fixes: 9ec37ef ("PCI/MSI: Make pci_host_common_probe() declare its reliance on MSI domains")
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jean-Philippe Brucker <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Acked-by: Marc Zyngier <[email protected]>

Author: jpbrucker

drivers/pci/of.c

@@ -103,6 +103,13 @@ struct irq_domain *pci_host_bridge_of_msi_domain(struct pci_bus *bus)
 #endif
 }
 
+bool pci_host_of_has_msi_map(struct device *dev)
+{
+	if (dev && dev->of_node)
+		return of_get_property(dev->of_node, "msi-map", NULL);
+	return false;
+}
+
 static inline int __of_pci_pci_compare(struct device_node *node,
 				       unsigned int data)
 {

drivers/pci/probe.c

@@ -925,7 +925,8 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	device_enable_async_suspend(bus->bridge);
 	pci_set_bus_of_node(bus);
 	pci_set_bus_msi_domain(bus);
-	if (bridge->msi_domain && !dev_get_msi_domain(&bus->dev))
+	if (bridge->msi_domain && !dev_get_msi_domain(&bus->dev) &&
+	    !pci_host_of_has_msi_map(parent))
 		bus->bus_flags |= PCI_BUS_FLAGS_NO_MSI;
 
 	if (!parent)

include/linux/pci.h

@@ -2344,13 +2344,15 @@ int pci_vpd_find_info_keyword(const u8 *buf, unsigned int off,
 struct device_node;
 struct irq_domain;
 struct irq_domain *pci_host_bridge_of_msi_domain(struct pci_bus *bus);
+bool pci_host_of_has_msi_map(struct device *dev);
 
 /* Arch may override this (weak) */
 struct device_node *pcibios_get_phb_of_node(struct pci_bus *bus);
 
 #else	/* CONFIG_OF */
 static inline struct irq_domain *
 pci_host_bridge_of_msi_domain(struct pci_bus *bus) { return NULL; }
+static inline bool pci_host_of_has_msi_map(struct device *dev) { return false; }
 #endif  /* CONFIG_OF */
 
 static inline struct device_node *