drm/edid: pass a timing pointer to is_display_descriptor()

Use struct member access instead of direct offsets to avoid lots of
casts all over the place.

Use BUILD_BUG_ON() for sanity check.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ccc54b45ea628874c0290dd64114da6cefff1819.1648477901.git.jani.nikula@intel.com

drivers/gpu/drm/drm_edid.c

@@ -2331,10 +2331,15 @@ struct drm_display_mode *drm_mode_find_dmt(struct drm_device *dev,
 }
 EXPORT_SYMBOL(drm_mode_find_dmt);
 
-static bool is_display_descriptor(const u8 d[18], u8 tag)
+static bool is_display_descriptor(const struct detailed_timing *descriptor, u8 type)
 {
-	return d[0] == 0x00 && d[1] == 0x00 &&
-		d[2] == 0x00 && d[3] == tag;
+	BUILD_BUG_ON(offsetof(typeof(*descriptor), pixel_clock) != 0);
+	BUILD_BUG_ON(offsetof(typeof(*descriptor), data.other_data.pad1) != 2);
+	BUILD_BUG_ON(offsetof(typeof(*descriptor), data.other_data.type) != 3);
+
+	return descriptor->pixel_clock == 0 &&
+		descriptor->data.other_data.pad1 == 0 &&
+		descriptor->data.other_data.type == type;
 }
 
 static bool is_detailed_timing_descriptor(const u8 d[18])
@@ -2405,7 +2410,7 @@ is_rb(struct detailed_timing *t, void *data)
 {
 	u8 *r = (u8 *)t;
 
-	if (!is_display_descriptor(r, EDID_DETAIL_MONITOR_RANGE))
+	if (!is_display_descriptor(t, EDID_DETAIL_MONITOR_RANGE))
 		return;
 
 	if (r[10] == DRM_EDID_CVT_SUPPORT_FLAG && r[15] & 0x10)
@@ -2431,7 +2436,7 @@ find_gtf2(struct detailed_timing *t, void *data)
 {
 	u8 *r = (u8 *)t;
 
-	if (!is_display_descriptor(r, EDID_DETAIL_MONITOR_RANGE))
+	if (!is_display_descriptor(t, EDID_DETAIL_MONITOR_RANGE))
 		return;
 
 	if (r[10] == 0x02)
@@ -2987,7 +2992,7 @@ do_inferred_modes(struct detailed_timing *timing, void *c)
 	struct detailed_non_pixel *data = &timing->data.other_data;
 	struct detailed_data_monitor_range *range = &data->data.range;
 
-	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_MONITOR_RANGE))
+	if (!is_display_descriptor(timing, EDID_DETAIL_MONITOR_RANGE))
 		return;
 
 	closure->modes += drm_dmt_modes_for_range(closure->connector,
@@ -3067,7 +3072,7 @@ do_established_modes(struct detailed_timing *timing, void *c)
 {
 	struct detailed_mode_closure *closure = c;
 
-	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_EST_TIMINGS))
+	if (!is_display_descriptor(timing, EDID_DETAIL_EST_TIMINGS))
 		return;
 
 	closure->modes += drm_est3_modes(closure->connector, timing);
@@ -3122,7 +3127,7 @@ do_standard_modes(struct detailed_timing *timing, void *c)
 	struct edid *edid = closure->edid;
 	int i;
 
-	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_STD_MODES))
+	if (!is_display_descriptor(timing, EDID_DETAIL_STD_MODES))
 		return;
 
 	for (i = 0; i < 6; i++) {
@@ -3231,7 +3236,7 @@ do_cvt_mode(struct detailed_timing *timing, void *c)
 {
 	struct detailed_mode_closure *closure = c;
 
-	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_CVT_3BYTE))
+	if (!is_display_descriptor(timing, EDID_DETAIL_CVT_3BYTE))
 		return;
 
 	closure->modes += drm_cvt_modes(closure->connector, timing);
@@ -4491,7 +4496,7 @@ drm_parse_hdmi_vsdb_audio(struct drm_connector *connector, const u8 *db)
 static void
 monitor_name(struct detailed_timing *t, void *data)
 {
-	if (!is_display_descriptor((const u8 *)t, EDID_DETAIL_MONITOR_NAME))
+	if (!is_display_descriptor(t, EDID_DETAIL_MONITOR_NAME))
 		return;
 
 	*(u8 **)data = t->data.other_data.data.str.str;
@@ -5221,7 +5226,7 @@ void get_monitor_range(struct detailed_timing *timing,
 	const struct detailed_non_pixel *data = &timing->data.other_data;
 	const struct detailed_data_monitor_range *range = &data->data.range;
 
-	if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_MONITOR_RANGE))
+	if (!is_display_descriptor(timing, EDID_DETAIL_MONITOR_RANGE))
 		return;
 
 	/*