drm/radeon/kms/agp The wrong AGP chipset can cause a NULL pointer der…

…eference

Selecting the wrong or no CONFIG_AGP_* chipset can cause a NULL pointer
dereference when combined with CONFIG_DRM_RADEON_KMS and an old system
with a R100 AGP card (should effect other cards too).  The agp field
will be set to NULL if no suitable AGP chipset driver is loaded,
drm_agp_acquire already preforms a suitable NULL check so it can be used
directly.

Signed-off-by: Robert Fitzsimons <robfitz@273k.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_agp.c

@@ -134,12 +134,10 @@ int radeon_agp_init(struct radeon_device *rdev)
 	int ret;
 
 	/* Acquire AGP. */
-	if (!rdev->ddev->agp->acquired) {
-		ret = drm_agp_acquire(rdev->ddev);
-		if (ret) {
-			DRM_ERROR("Unable to acquire AGP: %d\n", ret);
-			return ret;
-		}
+	ret = drm_agp_acquire(rdev->ddev);
+	if (ret) {
+		DRM_ERROR("Unable to acquire AGP: %d\n", ret);
+		return ret;
 	}
 
 	ret = drm_agp_info(rdev->ddev, &info);