drm/bridge: adv7533: Use internal timing generator

ADV7533 provides an internal timing generator for certain modes that it
can't use the DSI clock directly.

We've observed that HDMI is more stable with the internal timing
generator, especially if there are instabilities in the DSI clock source.
The data spec also seems to recommend the usage of the timing generator
for all modes.

However, on some platforms, it's reported that enabling the timing
generator causes instabilities with the HDMI output.

Create a DT parameter that lets a platform explicitly disable the timing
generator. The timing generator is enabled by default.
Signed-off-by: Archit Taneja <architt@codeaurora.org>

drivers/gpu/drm/bridge/adv7511/adv7511.h

@@ -306,6 +306,8 @@ struct adv7511 {
 	enum drm_connector_status status;
 	bool powered;
 
+	struct drm_display_mode curr_mode;
+
 	unsigned int f_tmds;
 
 	unsigned int current_edid_segment;
@@ -329,6 +331,7 @@ struct adv7511 {
 	struct device_node *host_node;
 	struct mipi_dsi_device *dsi;
 	u8 num_dsi_lanes;
+	bool use_timing_gen;
 
 	enum adv7511_type type;
 };

drivers/gpu/drm/bridge/adv7511/adv7511_drv.c

@@ -712,6 +712,8 @@ static void adv7511_mode_set(struct adv7511 *adv7511,
 	regmap_update_bits(adv7511->regmap, 0x17,
 		0x60, (vsync_polarity << 6) | (hsync_polarity << 5));
 
+	drm_mode_copy(&adv7511->curr_mode, adj_mode);
+
 	/*
 	 * TODO Test first order 4:2:2 to 4:4:4 up conversion method, which is
 	 * supposed to give better results.

drivers/gpu/drm/bridge/adv7511/adv7533.c

@@ -39,14 +39,65 @@ static const struct regmap_config adv7533_cec_regmap_config = {
 	.cache_type = REGCACHE_RBTREE,
 };
 
+static void adv7511_dsi_config_timing_gen(struct adv7511 *adv)
+{
+	struct mipi_dsi_device *dsi = adv->dsi;
+	struct drm_display_mode *mode = &adv->curr_mode;
+	unsigned int hsw, hfp, hbp, vsw, vfp, vbp;
+	u8 clock_div_by_lanes[] = { 6, 4, 3 };	/* 2, 3, 4 lanes */
+
+	hsw = mode->hsync_end - mode->hsync_start;
+	hfp = mode->hsync_start - mode->hdisplay;
+	hbp = mode->htotal - mode->hsync_end;
+	vsw = mode->vsync_end - mode->vsync_start;
+	vfp = mode->vsync_start - mode->vdisplay;
+	vbp = mode->vtotal - mode->vsync_end;
+
+	/* set pixel clock divider mode */
+	regmap_write(adv->regmap_cec, 0x16,
+		     clock_div_by_lanes[dsi->lanes - 2] << 3);
+
+	/* horizontal porch params */
+	regmap_write(adv->regmap_cec, 0x28, mode->htotal >> 4);
+	regmap_write(adv->regmap_cec, 0x29, (mode->htotal << 4) & 0xff);
+	regmap_write(adv->regmap_cec, 0x2a, hsw >> 4);
+	regmap_write(adv->regmap_cec, 0x2b, (hsw << 4) & 0xff);
+	regmap_write(adv->regmap_cec, 0x2c, hfp >> 4);
+	regmap_write(adv->regmap_cec, 0x2d, (hfp << 4) & 0xff);
+	regmap_write(adv->regmap_cec, 0x2e, hbp >> 4);
+	regmap_write(adv->regmap_cec, 0x2f, (hbp << 4) & 0xff);
+
+	/* vertical porch params */
+	regmap_write(adv->regmap_cec, 0x30, mode->vtotal >> 4);
+	regmap_write(adv->regmap_cec, 0x31, (mode->vtotal << 4) & 0xff);
+	regmap_write(adv->regmap_cec, 0x32, vsw >> 4);
+	regmap_write(adv->regmap_cec, 0x33, (vsw << 4) & 0xff);
+	regmap_write(adv->regmap_cec, 0x34, vfp >> 4);
+	regmap_write(adv->regmap_cec, 0x35, (vfp << 4) & 0xff);
+	regmap_write(adv->regmap_cec, 0x36, vbp >> 4);
+	regmap_write(adv->regmap_cec, 0x37, (vbp << 4) & 0xff);
+}
+
 void adv7533_dsi_power_on(struct adv7511 *adv)
 {
 	struct mipi_dsi_device *dsi = adv->dsi;
 
+	if (adv->use_timing_gen)
+		adv7511_dsi_config_timing_gen(adv);
+
 	/* set number of dsi lanes */
 	regmap_write(adv->regmap_cec, 0x1c, dsi->lanes << 4);
-	/* disable internal timing generator */
-	regmap_write(adv->regmap_cec, 0x27, 0x0b);
+
+	if (adv->use_timing_gen) {
+		/* reset internal timing generator */
+		regmap_write(adv->regmap_cec, 0x27, 0xcb);
+		regmap_write(adv->regmap_cec, 0x27, 0x8b);
+		regmap_write(adv->regmap_cec, 0x27, 0xcb);
+	} else {
+		/* disable internal timing generator */
+		regmap_write(adv->regmap_cec, 0x27, 0x0b);
+	}
+
 	/* enable hdmi */
 	regmap_write(adv->regmap_cec, 0x03, 0x89);
 	/* disable test mode */
@@ -60,6 +111,8 @@ void adv7533_dsi_power_off(struct adv7511 *adv)
 {
 	/* disable hdmi */
 	regmap_write(adv->regmap_cec, 0x03, 0x0b);
+	/* disable internal timing generator */
+	regmap_write(adv->regmap_cec, 0x27, 0x0b);
 }
 
 int adv7533_patch_registers(struct adv7511 *adv)
@@ -179,6 +232,9 @@ int adv7533_parse_dt(struct device_node *np, struct adv7511 *adv)
 	of_node_put(endpoint);
 	of_node_put(adv->host_node);
 
+	adv->use_timing_gen = !of_property_read_bool(np,
+						"adi,disable-timing-generator");
+
 	/* TODO: Check if these need to be parsed by DT or not */
 	adv->rgb = true;
 	adv->embedded_sync = false;