drm/amd/display: Detect dynamic backlight support in eDP sink

[Why]
Check if the eDP sink supports the dynamic backlight control

[How]
Query the dynamic backlight capability in DPCD (eDP case only)
Signed-off-by: Roy Chan <roy.chan@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c

@@ -3745,6 +3745,7 @@ void detect_edp_sink_caps(struct dc_link *link)
 	uint32_t entry;
 	uint32_t link_rate_in_khz;
 	enum dc_link_rate link_rate = LINK_RATE_UNKNOWN;
+	uint8_t backlight_adj_cap;
 
 	retrieve_link_cap(link);
 	link->dpcd_caps.edp_supported_link_rates_count = 0;
@@ -3775,6 +3776,12 @@ void detect_edp_sink_caps(struct dc_link *link)
 	}
 	link->verified_link_cap = link->reported_link_cap;
 
+	core_link_read_dpcd(link, DP_EDP_BACKLIGHT_ADJUSTMENT_CAP,
+						&backlight_adj_cap, sizeof(backlight_adj_cap));
+
+	link->dpcd_caps.dynamic_backlight_capable_edp =
+				(backlight_adj_cap & DP_EDP_DYNAMIC_BACKLIGHT_CAP) ? true:false;
+
 	dc_link_set_default_brightness_aux(link);
 }
 

drivers/gpu/drm/amd/display/dc/dc.h

@@ -1091,6 +1091,7 @@ struct dpcd_caps {
 	bool panel_mode_edp;
 	bool dpcd_display_control_capable;
 	bool ext_receiver_cap_field_present;
+	bool dynamic_backlight_capable_edp;
 	union dpcd_fec_capability fec_cap;
 	struct dpcd_dsc_capabilities dsc_caps;
 	struct dc_lttpr_caps lttpr_caps;