drm/dp: Introduce new member in drm_backlight_info

Introduce luminance_set flag which indicates if we can manipulate
backlight using luminance value or not which is only possible
after eDP v1.5.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://lore.kernel.org/r/20250620063445.3603086-2-suraj.kandpal@intel.com

Author: surajk8

drivers/gpu/drm/display/drm_dp_helper.c

@@ -4261,11 +4261,15 @@ drm_edp_backlight_init(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl
 		bl->aux_set = true;
 	if (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
 		bl->lsb_reg_used = true;
+	if ((edp_dpcd[0] & DP_EDP_15) && edp_dpcd[3] &
+	    (DP_EDP_PANEL_LUMINANCE_CONTROL_CAPABLE))
+		bl->luminance_set = true;
 
 	/* Sanity check caps */
-	if (!bl->aux_set && !(edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP)) {
+	if (!bl->aux_set && !(edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP) &&
+	    !bl->luminance_set) {
 		drm_dbg_kms(aux->drm_dev,
-			    "%s: Panel supports neither AUX or PWM brightness control? Aborting\n",
+			    "%s: Panel does not support AUX, PWM or luminance-based brightness control. Aborting\n",
 			    aux->name);
 		return -EINVAL;
 	}

include/drm/display/drm_dp_helper.h

@@ -849,6 +849,7 @@ struct drm_edp_backlight_info {
 	bool lsb_reg_used : 1;
 	bool aux_enable : 1;
 	bool aux_set : 1;
+	bool luminance_set : 1;
 };
 
 int