drm/amd/display: Adding support for VESA SCR

[HOW&WHY]
Write DPCD 721 bit 7 to high, and
the appropriate luminance level
to DPCD 734-736 if bit 4 from DPCD register
734 is high, indicating that the panel
luminance control is enabled from the panel side.
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Iswara Nagulendran <Iswara.Nagulendran@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -566,6 +566,12 @@ struct dpcd_amd_device_id {
 	uint8_t dal_version_byte2;
 };
 
+struct target_luminance_value {
+	uint8_t byte0;
+	uint8_t byte1;
+	uint8_t byte2;
+};
+
 struct dpcd_source_backlight_set {
 	struct  {
 		uint8_t byte0;
@@ -1225,6 +1231,7 @@ struct dpcd_caps {
 	union dp_main_line_channel_coding_cap channel_coding_cap;
 	union dp_sink_video_fallback_formats fallback_formats;
 	union dp_fec_capability1 fec_cap1;
+	bool panel_luminance_control;
 	union dp_cable_id cable_id;
 	uint8_t edp_rev;
 	union edp_alpm_caps alpm_caps;

drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c

@@ -1450,7 +1450,8 @@ bool read_is_mst_supported(struct dc_link *link)
  */
 static bool dpcd_read_sink_ext_caps(struct dc_link *link)
 {
-	uint8_t dpcd_data;
+	uint8_t dpcd_data = 0;
+	uint8_t edp_general_cap2 = 0;
 
 	if (!link)
 		return false;
@@ -1459,6 +1460,12 @@ static bool dpcd_read_sink_ext_caps(struct dc_link *link)
 		return false;
 
 	link->dpcd_sink_ext_caps.raw = dpcd_data;
+
+	if (core_link_read_dpcd(link, DP_EDP_GENERAL_CAP_2, &edp_general_cap2, 1) != DC_OK)
+		return false;
+
+	link->dpcd_caps.panel_luminance_control = (edp_general_cap2 & DP_EDP_PANEL_LUMINANCE_CONTROL_CAPABLE) != 0;
+
 	return true;
 }
 

drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c

@@ -164,14 +164,35 @@ bool edp_set_backlight_level_nits(struct dc_link *link,
 	*(uint16_t *)&dpcd_backlight_set.backlight_transition_time_ms = (uint16_t)transition_time_in_ms;
 
 
-	if (core_link_write_dpcd(link, DP_SOURCE_BACKLIGHT_LEVEL,
+	if (!link->dpcd_caps.panel_luminance_control) {
+		if (core_link_write_dpcd(link, DP_SOURCE_BACKLIGHT_LEVEL,
 			(uint8_t *)(&dpcd_backlight_set),
 			sizeof(dpcd_backlight_set)) != DC_OK)
-		return false;
+			return false;
 
-	if (core_link_write_dpcd(link, DP_SOURCE_BACKLIGHT_CONTROL,
+		if (core_link_write_dpcd(link, DP_SOURCE_BACKLIGHT_CONTROL,
 			&backlight_control, 1) != DC_OK)
-		return false;
+			return false;
+	} else {
+		const uint8_t backlight_enable = DP_EDP_PANEL_LUMINANCE_CONTROL_ENABLE;
+		struct target_luminance_value *target_luminance = NULL;
+
+		//if target luminance value is greater than 24 bits, clip the value to 24 bits
+		if (backlight_millinits > 0xFFFFFF)
+			backlight_millinits = 0xFFFFFF;
+
+		target_luminance = (struct target_luminance_value *)&backlight_millinits;
+
+		if (core_link_write_dpcd(link, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
+			&backlight_enable,
+			sizeof(backlight_enable)) != DC_OK)
+			return false;
+
+		if (core_link_write_dpcd(link, DP_EDP_PANEL_TARGET_LUMINANCE_VALUE,
+			(uint8_t *)(target_luminance),
+			sizeof(struct target_luminance_value)) != DC_OK)
+			return false;
+	}
 
 	return true;
 }

include/drm/display/drm_dp.h

@@ -983,6 +983,7 @@
 
 #define DP_EDP_GENERAL_CAP_2		    0x703
 # define DP_EDP_OVERDRIVE_ENGINE_ENABLED		(1 << 0)
+# define DP_EDP_PANEL_LUMINANCE_CONTROL_CAPABLE (1 << 4)
 
 #define DP_EDP_GENERAL_CAP_3		    0x704    /* eDP 1.4 */
 # define DP_EDP_X_REGION_CAP_MASK			(0xf << 0)
@@ -1008,6 +1009,7 @@
 # define DP_EDP_DYNAMIC_BACKLIGHT_ENABLE		(1 << 4)
 # define DP_EDP_REGIONAL_BACKLIGHT_ENABLE		(1 << 5)
 # define DP_EDP_UPDATE_REGION_BRIGHTNESS		(1 << 6) /* eDP 1.4 */
+# define DP_EDP_PANEL_LUMINANCE_CONTROL_ENABLE  (1 << 7)
 
 #define DP_EDP_BACKLIGHT_BRIGHTNESS_MSB     0x722
 #define DP_EDP_BACKLIGHT_BRIGHTNESS_LSB     0x723
@@ -1032,6 +1034,7 @@
 
 #define DP_EDP_DBC_MINIMUM_BRIGHTNESS_SET   0x732
 #define DP_EDP_DBC_MAXIMUM_BRIGHTNESS_SET   0x733
+#define DP_EDP_PANEL_TARGET_LUMINANCE_VALUE 0x734
 
 #define DP_EDP_REGIONAL_BACKLIGHT_BASE      0x740    /* eDP 1.4 */
 #define DP_EDP_REGIONAL_BACKLIGHT_0	    0x741    /* eDP 1.4 */