drm: Remove preempt_disable() from vblank timestamping code.

Preemption handling will get pushed into the kms
drivers in followup patches, to make timestamping
more robust and PREEMPT_RT friendly.
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_irq.c

@@ -586,11 +586,6 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev, int crtc,
 	 * code gets preempted or delayed for some reason.
 	 */
 	for (i = 0; i < DRM_TIMESTAMP_MAXRETRIES; i++) {
-		/* Disable preemption to make it very likely to
-		 * succeed in the first iteration even on PREEMPT_RT kernel.
-		 */
-		preempt_disable();
-
 		/* Get system timestamp before query. */
 		stime = ktime_get();
 
@@ -602,8 +597,6 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev, int crtc,
 		if (!drm_timestamp_monotonic)
 			mono_time_offset = ktime_get_monotonic_offset();
 
-		preempt_enable();
-
 		/* Return as no-op if scanout query unsupported or failed. */
 		if (!(vbl_status & DRM_SCANOUTPOS_VALID)) {
 			DRM_DEBUG("crtc %d : scanoutpos query failed [%d].\n",