We only want drm to ever attach to the primary pci device.

Intel 855 chips present the same pci id for both heads.  This prevents
us from attaching to the dummy second head.  All other chips that I
am aware of either only present a single pci id, or different ids
for each head so that we only match on the correct head.

Approved by:	kib@
MFC after:	2 weeks

sys/dev/drm/drmP.h

@@ -87,6 +87,7 @@ struct drm_file;
 #include <sys/agpio.h>
 #include <sys/mutex.h>
 #include <dev/pci/pcivar.h>
+#include <dev/pci/pcireg.h>
 #include <sys/selinfo.h>
 #include <sys/bus.h>
 

sys/dev/drm/drm_drv.c

@@ -152,6 +152,10 @@ int drm_probe(device_t dev, drm_pci_id_list_t *idlist)
 	device = pci_get_device(dev);
 #endif
 
+	if (pci_get_class(dev) != PCIC_DISPLAY
+	    || pci_get_subclass(dev) != PCIS_DISPLAY_VGA)
+		return ENXIO;
+
 	id_entry = drm_find_description(vendor, device, idlist);
 	if (id_entry != NULL) {
 		device_set_desc(dev, id_entry->name);