drm: add debug print to update_vblank_count

Since we are logging all vblank counter updates 30 lines below,
it is also good to have some details whether and how vblank count
difference is calculated.

Signed-off-by: Oleg Vasilev <oleg.vasilev@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190613121802.2193-1-oleg.vasilev@intel.com

drivers/gpu/drm/drm_vblank.c

@@ -241,12 +241,16 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
 		 * on the difference in the timestamps and the
 		 * frame/field duration.
 		 */
+
+		DRM_DEBUG_VBL("crtc %u: Calculating number of vblanks."
+			      " diff_ns = %lld, framedur_ns = %d)\n",
+			      pipe, (long long) diff_ns, framedur_ns);
+
 		diff = DIV_ROUND_CLOSEST_ULL(diff_ns, framedur_ns);
 
 		if (diff == 0 && in_vblank_irq)
-			DRM_DEBUG_VBL("crtc %u: Redundant vblirq ignored."
-				      " diff_ns = %lld, framedur_ns = %d)\n",
-				      pipe, (long long) diff_ns, framedur_ns);
+			DRM_DEBUG_VBL("crtc %u: Redundant vblirq ignored\n",
+				      pipe);
 	} else {
 		/* some kind of default for drivers w/o accurate vbl timestamping */
 		diff = in_vblank_irq ? 1 : 0;