drm/edid: Clarify why we only accept the "range limits only" descriptor

The current comment fails to clarify why we only accept
the "range limits only" variant of the range descriptor.
Reword it to make some actual sense.

Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Reviewed-by: NManasi Navare <manasi.d.navare@intel.com>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220927170006.27855-2-ville.syrjala@linux.intel.com

drivers/gpu/drm/drm_edid.c

@@ -6052,10 +6052,13 @@ void get_monitor_range(const struct detailed_timing *timing,
 		return;
 
 	/*
-	 * Check for flag range limits only. If flag == 1 then
-	 * no additional timing information provided.
-	 * Default GTF, GTF Secondary curve and CVT are not
-	 * supported
+	 * These limits are used to determine the VRR refresh
+	 * rate range. Only the "range limits only" variant
+	 * of the range descriptor seems to guarantee that
+	 * any and all timings are accepted by the sink, as
+	 * opposed to just timings conforming to the indicated
+	 * formula (GTF/GTF2/CVT). Thus other variants of the
+	 * range descriptor are not accepted here.
 	 */
 	if (range->flags != DRM_EDID_RANGE_LIMITS_ONLY_FLAG)
 		return;