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
@@ -313,32 +313,42 @@
 		0x96, 0x57, 0x74, 0x41, 0xc0, 0x3d, 0xd7, 0x66
 	};
 
-	/* Status Field */
-	cap_set[PCI_OSC_STATUS] = 0;
+	/*
+	 * Don't invoke _OSC if a control is already granted.
+	 * However, always invoke _OSC during attach when 0 is passed.
+	 */
+	if (osc_ctl != 0 && (sc->ap_osc_ctl & osc_ctl) == osc_ctl)
+		return (0);
 
 	/* Support Field: Extended PCI Config Space, MSI */
 	cap_set[PCI_OSC_SUPPORT] = PCIM_OSC_SUPPORT_EXT_PCI_CONF |
 	    PCIM_OSC_SUPPORT_MSI;
 
 	/* Control Field */
-	sc->ap_osc_ctl |= osc_ctl;
-	cap_set[PCI_OSC_CTL] = sc->ap_osc_ctl;
+	cap_set[PCI_OSC_CTL] = sc->ap_osc_ctl | osc_ctl;
 
 	status = acpi_EvaluateOSC(sc->ap_handle, pci_host_bridge_uuid, 1,
 	    nitems(cap_set), cap_set, cap_set, false);
 	if (ACPI_FAILURE(status)) {
-		if (status == AE_NOT_FOUND)
+		if (status == AE_NOT_FOUND) {
+			sc->ap_osc_ctl |= osc_ctl;
 			return (0);
+		}
 		device_printf(sc->ap_dev, "_OSC failed: %s\n",
 		    AcpiFormatException(status));
 		return (EIO);
 	}
 
-	if (cap_set[PCI_OSC_STATUS] == 0)
-		sc->ap_osc_ctl = cap_set[PCI_OSC_CTL];
-
-	if (cap_set[PCI_OSC_STATUS] != 0 ||
-	    (cap_set[PCI_OSC_CTL] & osc_ctl) != osc_ctl)
+	/*
+	 * _OSC may return an error in the status word, but will
+	 * update the control mask always.  _OSC should not revoke
+	 * previously-granted controls.
+	 */
+	if ((cap_set[PCI_OSC_CTL] & sc->ap_osc_ctl) != sc->ap_osc_ctl)
+		device_printf(sc->ap_dev, "_OSC revoked %#x\n",
+		    (cap_set[PCI_OSC_CTL] & sc->ap_osc_ctl) ^ sc->ap_osc_ctl);
+	sc->ap_osc_ctl = cap_set[PCI_OSC_CTL];
+	if ((sc->ap_osc_ctl & osc_ctl) != osc_ctl)
 		return (EIO);
 
 	return (0);
@@ -727,7 +737,7 @@
 	uint32_t osc_ctl;
 	struct acpi_hpcib_softc *sc;
 
-	sc = device_get_softc(dev);
+	sc = device_get_softc(pcib);
 
 	switch (feature) {
 	case PCI_FEATURE_HP:
Index: head/sys/dev/acpica/acpivar.h
===================================================================
--- head/sys/dev/acpica/acpivar.h
+++ head/sys/dev/acpica/acpivar.h
@@ -301,6 +301,12 @@
 	device_printf(dev, x);					\
 } while (0)
 
+/* Values for the first status word returned by _OSC. */
+#define	ACPI_OSC_FAILURE	(1 << 1)
+#define	ACPI_OSC_BAD_UUID	(1 << 2)
+#define	ACPI_OSC_BAD_REVISION	(1 << 3)
+#define	ACPI_OSC_CAPS_MASKED	(1 << 4)
+
 /* Values for the device _STA (status) method. */
 #define ACPI_STA_PRESENT	(1 << 0)
 #define ACPI_STA_ENABLED	(1 << 1)
Index: head/sys/dev/pci/pci_pci.c
===================================================================
--- head/sys/dev/pci/pci_pci.c
+++ head/sys/dev/pci/pci_pci.c
@@ -76,7 +76,7 @@
 static void		pcib_pcie_cc_timeout(void *arg);
 static void		pcib_pcie_dll_timeout(void *arg);
 #endif
-static int		pcib_request_feature(device_t pcib, device_t dev,
+static int		pcib_request_feature_default(device_t pcib, device_t dev,
 			    enum pci_feature feature);
 
 static device_method_t pcib_methods[] = {
@@ -121,7 +121,7 @@
     DEVMETHOD(pcib_try_enable_ari,	pcib_try_enable_ari),
     DEVMETHOD(pcib_ari_enabled,		pcib_ari_enabled),
     DEVMETHOD(pcib_decode_rid,		pcib_ari_decode_rid),
-    DEVMETHOD(pcib_request_feature,	pcib_request_feature),
+    DEVMETHOD(pcib_request_feature,	pcib_request_feature_default),
 
     DEVMETHOD_END
 };
@@ -964,8 +964,7 @@
 	 * Now that we're sure we want to do hot plug, ask the
 	 * firmware, if any, if that's OK.
 	 */
-	if (pcib_request_feature(device_get_parent(device_get_parent(dev)), dev,
-		PCI_FEATURE_HP) != 0) {
+	if (pcib_request_feature(dev, PCI_FEATURE_HP) != 0) {
 		if (bootverbose)
 			device_printf(dev, "Unable to activate hot plug feature.\n");
 		return;
@@ -2863,6 +2862,17 @@
 	return (0);
 }
 
+int
+pcib_request_feature(device_t dev, enum pci_feature feature)
+{
+
+	/*
+	 * Invoke PCIB_REQUEST_FEATURE of this bridge first in case
+	 * the firmware overrides the method of PCI-PCI bridges.
+	 */
+	return (PCIB_REQUEST_FEATURE(dev, dev, feature));
+}
+
 /*
  * Pass the request to use this PCI feature up the tree. Either there's a
  * firmware like ACPI that's using this feature that will approve (or deny) the
@@ -2871,7 +2881,8 @@
  * to make use of the feature or render it harmless.
  */
 static int
-pcib_request_feature(device_t pcib, device_t dev, enum pci_feature feature)
+pcib_request_feature_default(device_t pcib, device_t dev,
+    enum pci_feature feature)
 {
 	device_t bus;
 
Index: head/sys/dev/pci/pcib_private.h
===================================================================
--- head/sys/dev/pci/pcib_private.h
+++ head/sys/dev/pci/pcib_private.h
@@ -193,6 +193,7 @@
 		    uintptr_t *id);
 void		pcib_decode_rid(device_t pcib, uint16_t rid, int *bus, 
 		    int *slot, int *func);
+int		pcib_request_feature(device_t dev, enum pci_feature feature);
 int		pcib_request_feature_allow(device_t pcib, device_t dev, enum pci_feature feature);
 
 #endif