drm: fd.o bug #11895: Only add the AGP base to map offset if the caller didn't.

The i830 and newer intel 2D code adds the AGP base to map offsets already,
because it wasn't doing the AGP enable which used to set dev->agp->base.

Credit goes to Zhenyu for finding the issue.
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/drm_bufs.c

@@ -229,11 +229,17 @@ static int drm_addmap_core(struct drm_device * dev, unsigned int offset,
 #ifdef __alpha__
 		map->offset += dev->hose->mem_space->start;
 #endif
-		/* Note: dev->agp->base may actually be 0 when the DRM
-		 * is not in control of AGP space. But if user space is
-		 * it should already have added the AGP base itself.
+		/* In some cases (i810 driver), user space may have already
+		 * added the AGP base itself, because dev->agp->base previously
+		 * only got set during AGP enable.  So, only add the base
+		 * address if the map's offset isn't already within the
+		 * aperture.
 		 */
+		if (map->offset < dev->agp->base ||
+		    map->offset > dev->agp->base +
+		    dev->agp->agp_info.aper_size * 1024 * 1024 - 1) {
 			map->offset += dev->agp->base;
+		}
 		map->mtrr = dev->agp->agp_mtrr;	/* for getmap */
 
 		/* This assumes the DRM is in total control of AGP space.