Index: head/sys/dev/acpica/acpi_pcib_acpi.c
===================================================================
--- head/sys/dev/acpica/acpi_pcib_acpi.c
+++ head/sys/dev/acpica/acpi_pcib_acpi.c
@@ -295,6 +295,40 @@
 }
 #endif
 
+static void
+acpi_pcib_osc(struct acpi_hpcib_softc *sc)
+{
+	ACPI_STATUS status;
+	uint32_t cap_set[3];
+
+	static uint8_t pci_host_bridge_uuid[ACPI_UUID_LENGTH] = {
+		0x5b, 0x4d, 0xdb, 0x33, 0xf7, 0x1f, 0x1c, 0x40,
+		0x96, 0x57, 0x74, 0x41, 0xc0, 0x3d, 0xd7, 0x66
+	};
+
+	/* Support Field: Extended PCI Config Space, MSI */
+	cap_set[1] = 0x11;
+
+	/* Control Field */
+	cap_set[2] = 0;
+
+	status = acpi_EvaluateOSC(sc->ap_handle, pci_host_bridge_uuid, 1,
+	    nitems(cap_set), cap_set, false);
+	if (ACPI_FAILURE(status)) {
+		if (status == AE_NOT_FOUND)
+			return;
+		device_printf(sc->ap_dev, "_OSC failed: %s\n",
+		    AcpiFormatException(status));
+		return;
+	}
+
+	if (cap_set[0] != 0) {
+		device_printf(sc->ap_dev, "_OSC returned error %#x\n",
+		    cap_set[0]);
+		return;
+	}
+}
+
 static int
 acpi_pcib_acpi_attach(device_t dev)
 {
@@ -321,6 +355,8 @@
     if (!acpi_DeviceIsPresent(dev))
 	return (ENXIO);
 
+    acpi_pcib_osc(sc);
+
     /*
      * Get our segment number by evaluating _SEG.
      * It's OK for this to not exist.