x86/pci: Set default irq domain in pcibios_add_device()

Now that interrupt remapping sets the irqdomain pointer when a PCI device
is added it's possible to store the default irq domain in the device struct
in pcibios_add_device().

If the bus to which a device is connected has an irq domain associated then
this domain is used otherwise the default domain (PCI/MSI native or XEN
PCI/MSI) is used. Using the bus domain ensures that special MSI bus domains
like VMD work.

This makes XEN and the non-remapped native case work solely based on the
irq domain pointer in struct device for PCI/MSI and allows to remove the
arch fallback and make most of the x86_msi ops private to XEN in the next
steps.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20200826112333.900423047@linutronix.de

arch/x86/include/asm/irqdomain.h

@@ -53,9 +53,11 @@ extern int mp_irqdomain_ioapic_idx(struct irq_domain *domain);
 #ifdef CONFIG_PCI_MSI
 void x86_create_pci_msi_domain(void);
 struct irq_domain *native_create_pci_msi_domain(void);
+extern struct irq_domain *x86_pci_msi_default_domain;
 #else
 static inline void x86_create_pci_msi_domain(void) { }
 #define native_create_pci_msi_domain	NULL
+#define x86_pci_msi_default_domain	NULL
 #endif
 
 #endif

arch/x86/kernel/apic/msi.c

@@ -21,7 +21,7 @@
 #include <asm/apic.h>
 #include <asm/irq_remapping.h>
 
-static struct irq_domain *x86_pci_msi_default_domain __ro_after_init;
+struct irq_domain *x86_pci_msi_default_domain __ro_after_init;
 
 static void __irq_msi_compose_msg(struct irq_cfg *cfg, struct msi_msg *msg)
 {

arch/x86/pci/common.c

@@ -19,6 +19,7 @@
 #include <asm/smp.h>
 #include <asm/pci_x86.h>
 #include <asm/setup.h>
+#include <asm/irqdomain.h>
 
 unsigned int pci_probe = PCI_PROBE_BIOS | PCI_PROBE_CONF1 | PCI_PROBE_CONF2 |
 				PCI_PROBE_MMCONF;
@@ -633,8 +634,9 @@ static void set_dev_domain_options(struct pci_dev *pdev)
 
 int pcibios_add_device(struct pci_dev *dev)
 {
-	struct setup_data *data;
 	struct pci_setup_rom *rom;
+	struct irq_domain *msidom;
+	struct setup_data *data;
 	u64 pa_data;
 
 	pa_data = boot_params.hdr.setup_data;
@@ -661,6 +663,20 @@ int pcibios_add_device(struct pci_dev *dev)
 		memunmap(data);
 	}
 	set_dev_domain_options(dev);
+
+	/*
+	 * Setup the initial MSI domain of the device. If the underlying
+	 * bus has a PCI/MSI irqdomain associated use the bus domain,
+	 * otherwise set the default domain. This ensures that special irq
+	 * domains e.g. VMD are preserved. The default ensures initial
+	 * operation if irq remapping is not active. If irq remapping is
+	 * active it will overwrite the domain pointer when the device is
+	 * associated to a remapping domain.
+	 */
+	msidom = dev_get_msi_domain(&dev->bus->dev);
+	if (!msidom)
+		msidom = x86_pci_msi_default_domain;
+	dev_set_msi_domain(&dev->dev, msidom);
 	return 0;
 }