drm: Disallow DRM_IOCTL_MODESET_CTL for KMS drivers

DRM_IOCTL_MODESET_CTL must only be used for UMS drivers. Make it a no-op
for KMS drivers.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NMichel Dänzer <michel@daenzer.net>
Signed-off-by: NDave Airlie <airlied@gmail.com>

drivers/gpu/drm/drm_irq.c

@@ -974,7 +974,6 @@ EXPORT_SYMBOL(drm_vblank_off);
  * drm_vblank_pre_modeset - account for vblanks across mode sets
  * @dev: DRM device
  * @crtc: CRTC in question
- * @post: post or pre mode set?
  *
  * Account for vblank events across mode setting events, which will likely
  * reset the hardware frame counter.
@@ -1037,6 +1036,10 @@ int drm_modeset_ctl(struct drm_device *dev, void *data,
 	if (!dev->num_crtcs)
 		return 0;
 
+	/* KMS drivers handle this internally */
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		return 0;
+
 	crtc = modeset->crtc;
 	if (crtc >= dev->num_crtcs)
 		return -EINVAL;