Add a new method PCI_FIND_EXTCAP() to the pci bus interface that is used

to search for a specific extended capability.  If the specified capability
is found for the given device, then the function returns success and
optionally returns the offset of that capability.  If the capability is
not found, the function returns an error.

sys/dev/acpica/acpi_pci.c

@@ -117,6 +117,7 @@ static device_method_t acpi_pci_methods[] = {
 	DEVMETHOD(pci_get_powerstate,	pci_get_powerstate_method),
 	DEVMETHOD(pci_set_powerstate,	acpi_pci_set_powerstate_method),
 	DEVMETHOD(pci_assign_interrupt, pci_assign_interrupt_method),
+	DEVMETHOD(pci_find_extcap,	pci_find_extcap_method),
 
 	{ 0, 0 }
 };

sys/dev/pci/pci.c

@@ -133,6 +133,7 @@ static device_method_t pci_methods[] = {
 	DEVMETHOD(pci_get_powerstate,	pci_get_powerstate_method),
 	DEVMETHOD(pci_set_powerstate,	pci_set_powerstate_method),
 	DEVMETHOD(pci_assign_interrupt,	pci_assign_interrupt_method),
+	DEVMETHOD(pci_find_extcap,	pci_find_extcap_method),
 
 	{ 0, 0 }
 };
@@ -449,10 +450,10 @@ pci_read_extcap(device_t pcib, pcicfgregs *cfg)
 		}
 		/* Find the next entry */
 		ptr = nextptr;
-		nextptr = REG(ptr + 1, 1);
+		nextptr = REG(ptr + PCICAP_NEXTPTR, 1);
 
 		/* Process this entry */
-		switch (REG(ptr, 1)) {
+		switch (REG(ptr + PCICAP_ID, 1)) {
 		case PCIY_PMG:		/* PCI power management */
 			if (cfg->pp.pp_cap == 0) {
 				cfg->pp.pp_cap = REG(ptr + PCIR_POWER_CAP, 2);
@@ -477,6 +478,57 @@ pci_read_extcap(device_t pcib, pcicfgregs *cfg)
 #undef REG
 }
 
+/*
+ * Return the offset in configuration space of the requested extended
+ * capability entry or 0 if the specified capability was not found.
+ */
+int
+pci_find_extcap_method(device_t dev, device_t child, int capability,
+    int *capreg)
+{
+	struct pci_devinfo *dinfo = device_get_ivars(child);
+	pcicfgregs *cfg = &dinfo->cfg;
+	u_int32_t status;
+	u_int8_t ptr;
+
+	/*
+	 * Check the CAP_LIST bit of the PCI status register first.
+	 */
+	status = pci_read_config(child, PCIR_STATUS, 2);
+	if (!(status & PCIM_STATUS_CAPPRESENT))
+		return (ENXIO);
+
+	/*
+	 * Determine the start pointer of the capabilities list.
+	 */
+	switch (cfg->hdrtype & PCIM_HDRTYPE) {
+	case 0:
+		ptr = PCIR_CAP_PTR;
+		break;
+	case 2:
+		ptr = PCIR_CAP_PTR_2;
+		break;
+	default:
+		/* XXX: panic? */
+		return (ENXIO);		/* no extended capabilities support */
+	}
+	ptr = pci_read_config(child, ptr, 1);
+
+	/*
+	 * Traverse the capabilities list.
+	 */
+	while (ptr != 0) {
+		if (pci_read_config(child, ptr + PCICAP_ID, 1) == capability) {
+			if (capreg != NULL)
+				*capreg = ptr;
+			return (0);
+		}
+		ptr = pci_read_config(child, ptr + PCICAP_NEXTPTR, 1);
+	}
+
+	return (ENOENT);
+}
+
 /* free pcicfgregs structure and all depending data structures */
 
 int

sys/dev/pci/pci_if.m

@@ -82,3 +82,10 @@ METHOD int assign_interrupt {
 	device_t	dev;
 	device_t	child;
 };
+
+METHOD int find_extcap {
+	device_t	dev;
+	device_t	child;
+	int		capability;
+	int		*capreg;
+};

sys/dev/pci/pci_private.h

@@ -59,6 +59,8 @@ int		pci_enable_busmaster_method(device_t dev, device_t child);
 int		pci_disable_busmaster_method(device_t dev, device_t child);
 int		pci_enable_io_method(device_t dev, device_t child, int space);
 int		pci_disable_io_method(device_t dev, device_t child, int space);
+int		pci_find_extcap_method(device_t dev, device_t child,
+		    int capability, int *capreg);
 struct resource	*pci_alloc_resource(device_t dev, device_t child, 
 		    int type, int *rid, u_long start, u_long end, u_long count,
 		    u_int flags);

sys/dev/pci/pcireg.h

@@ -88,6 +88,11 @@
 #define PCIM_MFDEV		0x80
 #define PCIR_BIST	0x0f
 
+/* Capability Register Offsets */
+
+#define	PCICAP_ID	0x0
+#define	PCICAP_NEXTPTR	0x1
+
 /* Capability Identification Numbers */
 
 #define PCIY_PMG	0x01	/* PCI Power Management */

sys/dev/pci/pcivar.h

@@ -348,6 +348,12 @@ pci_get_powerstate(device_t dev)
     return PCI_GET_POWERSTATE(device_get_parent(dev), dev);
 }
 
+static __inline int
+pci_find_extcap(device_t dev, int capability, int *capreg)
+{
+    return PCI_FIND_EXTCAP(device_get_parent(dev), dev, capability, capreg);
+}
+
 device_t pci_find_bsf(uint8_t, uint8_t, uint8_t);
 device_t pci_find_device(uint16_t, uint16_t);
 #endif	/* _SYS_BUS_H_ */

sys/sparc64/pci/ofw_pcibus.c

@@ -106,6 +106,7 @@ static device_method_t ofw_pcibus_methods[] = {
 	DEVMETHOD(pci_get_powerstate,	pci_get_powerstate_method),
 	DEVMETHOD(pci_set_powerstate,	pci_set_powerstate_method),
 	DEVMETHOD(pci_assign_interrupt, ofw_pcibus_assign_interrupt),
+	DEVMETHOD(pci_find_extcap,	pci_find_extcap_method),
 
 	/* ofw_bus interface */
 	DEVMETHOD(ofw_bus_get_devinfo,	ofw_pcibus_get_devinfo),