drm/i915: Also record time difference if vblank evasion fails, v2.

This makes the error message slightly more useful.

Changes since v1:
- Use ktime_get() while irqs are still disabled. (vsyrjala)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 8f8d320..090d67b 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -564,6 +564,8 @@
 	int scanline_offset;
 
 	unsigned start_vbl_count;
+	ktime_t start_vbl_time;
+
 	struct intel_crtc_atomic_commit atomic;
 
 	/* scalers available on this crtc */