irqdomain/msi: Provide DOMAIN_BUS_VMD_MSI

PCI devices behind a VMD bus are not subject to interrupt remapping, but
the irq domain for VMD MSI cannot be distinguished from a regular PCI/MSI
irq domain.

Add a new domain bus token and allow it in the bus token check in
msi_check_reservation_mode() to keep the functionality the same once VMD
uses this token.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Marc Zyngier <maz@kernel.org>
Acked-by: Jon Derrick <jonathan.derrick@intel.com>
Link: https://lore.kernel.org/r/20200826112332.954409970@linutronix.de

include/linux/irqdomain.h

@@ -84,6 +84,7 @@ enum irq_domain_bus_token {
 	DOMAIN_BUS_FSL_MC_MSI,
 	DOMAIN_BUS_TI_SCI_INTA_MSI,
 	DOMAIN_BUS_WAKEUP,
+	DOMAIN_BUS_VMD_MSI,
 };
 
 /**

kernel/irq/msi.c

@@ -364,8 +364,13 @@ static bool msi_check_reservation_mode(struct irq_domain *domain,
 {
 	struct msi_desc *desc;
 
-	if (domain->bus_token != DOMAIN_BUS_PCI_MSI)
+	switch(domain->bus_token) {
+	case DOMAIN_BUS_PCI_MSI:
+	case DOMAIN_BUS_VMD_MSI:
+		break;
+	default:
 		return false;
+	}
 
 	if (!(info->flags & MSI_FLAG_MUST_REACTIVATE))
 		return false;