drm/i915/backlight: Use proper interface based on eDP version

eDP is supposed to use VESA interface when using revision 1.5 and above,
use Intel interface for backlight control otherwise. Add check to
use correct interface.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Tested-by: Ben Kao <ben.kao@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250206063253.2827017-4-suraj.kandpal@intel.com

Author: surajk8

drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c

@@ -604,6 +604,7 @@ static const struct intel_panel_bl_funcs intel_dp_vesa_bl_funcs = {
 int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 {
 	struct intel_display *display = to_intel_display(connector);
+	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct drm_device *dev = connector->base.dev;
 	struct intel_panel *panel = &connector->panel;
 	bool try_intel_interface = false, try_vesa_interface = false;
@@ -640,6 +641,10 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 		break;
 	}
 
+	/* For eDP 1.5 and above we are supposed to use VESA interface for brightness control */
+	if (intel_dp->edp_dpcd[0] >= DP_EDP_15)
+		try_vesa_interface = true;
+
 	/*
 	 * Since Intel has their own backlight control interface, the majority of machines out there
 	 * using DPCD backlight controls with Intel GPUs will be using this interface as opposed to
@@ -653,7 +658,8 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
 	 * backlight interface at all. This means that the only sensible way for us to detect both
 	 * interfaces is to probe for Intel's first, and VESA's second.
 	 */
-	if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector)) {
+	if (try_intel_interface && intel_dp_aux_supports_hdr_backlight(connector) &&
+	    intel_dp->edp_dpcd[0] <= DP_EDP_14b) {
 		drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Using Intel proprietary eDP backlight controls\n",
 			    connector->base.base.id, connector->base.name);
 		panel->backlight.funcs = &intel_dp_hdr_bl_funcs;