drm/edid: Introduce is_detailed_timing_descritor()

Let's introduce is_detailed_timing_descritor() as the opposite
counterpart of is_display_descriptor().

Cc: Allen Chen <allen.chen@ite.com.tw>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200124200231.10517-3-ville.syrjala@linux.intel.comAcked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>

drivers/gpu/drm/drm_edid.c

@@ -2218,6 +2218,11 @@ static bool is_display_descriptor(const u8 d[18], u8 tag)
 		d[2] == 0x00 && d[3] == tag;
 }
 
+static bool is_detailed_timing_descriptor(const u8 d[18])
+{
+	return d[0] != 0x00 || d[1] != 0x00;
+}
+
 typedef void detailed_cb(struct detailed_timing *timing, void *closure);
 
 static void
@@ -3117,7 +3122,9 @@ do_detailed_mode(struct detailed_timing *timing, void *c)
 	struct detailed_mode_closure *closure = c;
 	struct drm_display_mode *newmode;
 
-	if (timing->pixel_clock) {
+	if (!is_detailed_timing_descriptor((const u8 *)timing))
+		return;
+
 	newmode = drm_mode_detailed(closure->connector->dev,
 				    closure->edid, timing,
 				    closure->quirks);
@@ -3137,7 +3144,6 @@ do_detailed_mode(struct detailed_timing *timing, void *c)
 	drm_mode_probed_add(closure->connector, newmode);
 	closure->modes++;
 	closure->preferred = false;
-	}
 }
 
 /*