trogdor: Add backlight support for sn65dsi86bridge for Homestar

Add backlight support in sn65dsi86bridge through the AUX channel using
eDP DPCD registers, which is needed on the GOOGLE_HOMESTAR board.

Change-Id: Ie700080f1feabe2d3397c38088a64cff27bfbe55
Signed-off-by: Vinod Polimera <vpolimer@codeaurora.org>
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52663
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/drivers/ti/sn65dsi86bridge/sn65dsi86bridge.c

@@ -31,6 +31,14 @@
 #define DP_MAX_SUPPORTED_RATES		8 /* 16-bit little-endian */
 #define DP_LANE_COUNT_MASK		0xf
 
+/* Backlight configuration */
+#define DP_BACKLIGHT_MODE_SET			0x721
+#define DP_BACKLIGHT_CONTROL_MODE_MASK		0x3
+#define DP_BACKLIGHT_CONTROL_MODE_DPCD		0x2
+#define DP_DISPLAY_CONTROL_REGISTER		0x720
+#define DP_BACKLIGHT_ENABLE			0x1
+#define DP_BACKLIGHT_BRIGHTNESS_MSB		0x722
+
 /* link configuration */
 #define DP_LINK_BW_SET		0x100
 #define DP_LINK_BW_1_62		0x06
@@ -497,6 +505,20 @@ static void sn65dsi86_bridge_link_training(uint8_t bus, uint8_t chip)
 	printk(BIOS_ERR, "ERROR: Link training failed 10 times\n");
 }
 
+void sn65dsi86_backlight_enable(uint8_t bus, uint8_t chip)
+{
+	uint8_t val = DP_BACKLIGHT_CONTROL_MODE_DPCD;
+	sn65dsi86_bridge_aux_request(bus, chip, DP_BACKLIGHT_MODE_SET, 1, DPCD_WRITE, &val);
+
+	val = 0xff;
+	sn65dsi86_bridge_aux_request(bus, chip, DP_BACKLIGHT_BRIGHTNESS_MSB, 1,
+				     DPCD_WRITE, &val);
+
+	val = DP_BACKLIGHT_ENABLE;
+	sn65dsi86_bridge_aux_request(bus, chip, DP_DISPLAY_CONTROL_REGISTER, 1,
+				     DPCD_WRITE, &val);
+}
+
 static void sn65dsi86_bridge_assr_config(uint8_t bus, uint8_t chip, int enable)
 {
 	if (enable)

src/drivers/ti/sn65dsi86bridge/sn65dsi86bridge.h

@@ -18,5 +18,6 @@ void sn65dsi86_bridge_configure(uint8_t bus, uint8_t chip,
 				struct edid *edid, uint32_t num_of_lines,
 				uint32_t dsi_bpp);
 enum cb_err sn65dsi86_bridge_read_edid(uint8_t bus, uint8_t chip, struct edid *out);
+void sn65dsi86_backlight_enable(uint8_t bus, uint8_t chip);
 
 #endif

src/mainboard/google/trogdor/Kconfig

@@ -7,6 +7,11 @@ if BOARD_GOOGLE_TROGDOR_COMMON
 config TROGDOR_REV0
 	def_bool n
 
+config TROGDOR_HAS_BRIDGE_BACKLIGHT
+	bool
+	default y if BOARD_GOOGLE_HOMESTAR
+	default n
+
 config TROGDOR_HAS_FINGERPRINT
 	bool
 	default y if BOARD_GOOGLE_COACHZ

src/mainboard/google/trogdor/mainboard.c

@@ -83,6 +83,9 @@ static void display_init(struct edid *edid)
 		return;
 
 	sn65dsi86_bridge_configure(BRIDGE_BUS, BRIDGE_CHIP, edid, lanes, dsi_bpp);
+	if (CONFIG(TROGDOR_HAS_BRIDGE_BACKLIGHT))
+		sn65dsi86_backlight_enable(BRIDGE_BUS, BRIDGE_CHIP);
+
 	mdp_dsi_video_config(edid);
 	mdss_dsi_video_mode_config(edid, dsi_bpp);
 	mdp_dsi_video_on();