I think that if a PCI bus is a root bus, attached to a host bridge not a PCI->PCI bridge, then bus->self is allowed to be NULL. Certainly that's the case on my Pegasos, and it makes the MGA DRM driver oops...

Signed-off-by: David Woodhouse <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/char/drm/mga_drv.c

···
 	 * device.
 	 */
 
-	if ((pdev->device == 0x0525)
+	if ((pdev->device == 0x0525) && pdev->bus->self
 	    && (pdev->bus->self->vendor == 0x3388)
 	    && (pdev->bus->self->device == 0x0021)) {
 		return 0;