Index: sys/dev/pci/pci_host_generic_acpi.c
===================================================================
--- sys/dev/pci/pci_host_generic_acpi.c
+++ sys/dev/pci/pci_host_generic_acpi.c
@@ -348,14 +348,52 @@
 	return (acpi_pcib_route_interrupt(bus, dev, pin, &sc->ap_prt));
 }
 
+static u_int
+generic_pcie_get_xref(device_t pci, device_t child)
+{
+	struct generic_pcie_acpi_softc *sc;
+	uintptr_t rid;
+	u_int xref, devid;
+	int err;
+
+	sc = device_get_softc(pci);
+	err = pcib_get_id(pci, child, PCI_ID_RID, &rid);
+	if (err != 0)
+		return (ACPI_MSI_XREF);
+	err = acpi_iort_map_pci_msi(sc->base.ecam, rid, &xref, &devid);
+	if (err != 0)
+		return (ACPI_MSI_XREF);
+	return (xref);
+}
+
+static u_int
+generic_pcie_map_id(device_t pci, device_t child, uintptr_t *id)
+{
+	struct generic_pcie_acpi_softc *sc;
+	uintptr_t rid;
+	u_int xref, devid;
+	int err;
+
+	sc = device_get_softc(pci);
+	err = pcib_get_id(pci, child, PCI_ID_RID, &rid);
+	if (err != 0)
+		return (err);
+        err = acpi_iort_map_pci_msi(sc->base.ecam, rid, &xref, &devid);
+	if (err == 0)
+		*id = devid;
+	else
+		*id = rid;	/* RID not in IORT, likely FW bug, ignore */
+	return (0);
+}
+
 static int
 generic_pcie_acpi_alloc_msi(device_t pci, device_t child, int count,
     int maxcount, int *irqs)
 {
 
 #if defined(INTRNG)
-	return (intr_alloc_msi(pci, child, ACPI_MSI_XREF, count, maxcount,
-	    irqs));
+	return (intr_alloc_msi(pci, child, generic_pcie_get_xref(pci, child),
+	    count, maxcount, irqs));
 #else
 	return (ENXIO);
 #endif
@@ -367,7 +405,8 @@
 {
 
 #if defined(INTRNG)
-	return (intr_release_msi(pci, child, ACPI_MSI_XREF, count, irqs));
+	return (intr_release_msi(pci, child, generic_pcie_get_xref(pci, child),
+	    count, irqs));
 #else
 	return (ENXIO);
 #endif
@@ -379,7 +418,8 @@
 {
 
 #if defined(INTRNG)
-	return (intr_map_msi(pci, child, ACPI_MSI_XREF, irq, addr, data));
+	return (intr_map_msi(pci, child, generic_pcie_get_xref(pci, child), irq,
+	    addr, data));
 #else
 	return (ENXIO);
 #endif
@@ -390,7 +430,8 @@
 {
 
 #if defined(INTRNG)
-	return (intr_alloc_msix(pci, child, ACPI_MSI_XREF, irq));
+	return (intr_alloc_msix(pci, child, generic_pcie_get_xref(pci, child),
+	    irq));
 #else
 	return (ENXIO);
 #endif
@@ -401,7 +442,8 @@
 {
 
 #if defined(INTRNG)
-	return (intr_release_msix(pci, child, ACPI_MSI_XREF, irq));
+	return (intr_release_msix(pci, child, generic_pcie_get_xref(pci, child),
+	    irq));
 #else
 	return (ENXIO);
 #endif
@@ -412,14 +454,8 @@
     uintptr_t *id)
 {
 
-	/*
-	 * Use the PCI RID to find the MSI ID for now, we support only 1:1
-	 * mapping
-	 *
-	 * On aarch64, more complex mapping would come from IORT table
-	 */
 	if (type == PCI_ID_MSI)
-		return (pcib_get_id(pci, child, PCI_ID_RID, id));
+		return (generic_pcie_map_id(pci, child, id));
 	else
 		return (pcib_get_id(pci, child, type, id));
 }