PCI/MSI: Allow an msi_controller to be associated to an irq domain

With the new stacked irq domains, it becomes pretty tempting to
allocate an MSI domain per PCI bus, which would remove the requirement
of either relying on arch-specific code, or a default PCI MSI domain.

By allowing the msi_controller structure to carry a pointer to an
irq_domain, we can easily use this in pci_msi_setup_msi_irqs. The
existing code can still be used as a fallback if the MSI driver does
not populate the domain field.

Tested on arm64 with the GICv3 ITS driver.

Signed-off-by: Marc Zyngier <[e-mail]>
Cc: Yingjoe Chen <[e-mail]>
Cc: Bjorn Helgaas <[e-mail]>
Cc: [e-mail]
Cc: Jiang Liu <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

drivers/pci/msi.c

···
 	return pci_msi_default_domain;
 }
 
+static struct irq_domain *pci_msi_get_domain(struct pci_dev *dev)
+{
+	struct irq_domain *domain = NULL;
+
+	if (dev->bus->msi)
+		domain = dev->bus->msi->domain;
+	if (!domain)
+		domain = arch_get_pci_msi_domain(dev);
+
+	return domain;
+}
+
 static int pci_msi_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
 {
 	struct irq_domain *domain;
 
-	domain = arch_get_pci_msi_domain(dev);
+	domain = pci_msi_get_domain(dev);
 	if (domain)
 		return pci_msi_domain_alloc_irqs(domain, dev, nvec, type);
 
···
 {
 	struct irq_domain *domain;
 
-	domain = arch_get_pci_msi_domain(dev);
+	domain = pci_msi_get_domain(dev);
 	if (domain)
 		pci_msi_domain_free_irqs(domain, dev);
 	else

include/linux/msi.h

···
 	struct device *dev;
 	struct device_node *of_node;
 	struct list_head list;
+#ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
+	struct irq_domain *domain;
+#endif
 
 	int (*setup_irq)(struct msi_controller *chip, struct pci_dev *dev,
 			 struct msi_desc *desc);