drm: bridge: ldb: add support for using channel 1 only

The LDB driver currently checks whether dual mode is used, otherwise it
assumes only channel 0 is in use. Add support for using only channel 1. In
device tree terms, this means linking port 2 only.

Doing this cleanly requires changing the logic of the probe functions from
this:

 1. use of_graph_get_remote_node() on port 1 to find the panel
 2. use drm_of_lvds_get_dual_link_pixel_order() to detect dual mode

to this:

 1. use of_graph_get_remote_node() twice to find remote ports
 2. reuse the result of the above to know whether each channel is enabled
    and to find the panel
 3. if (both channels as enabled)
        use drm_of_lvds_get_dual_link_pixel_order() to detect dual mode

Also add a dev_dbg() to log the detected mode and log an error in case no
panel was found (no channel enabled).
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230405081058.2347130-2-luca.ceresoli@bootlin.com

drivers/gpu/drm/bridge/fsl-ldb.c

@@ -84,10 +84,16 @@ struct fsl_ldb {
 	struct drm_bridge *panel_bridge;
 	struct clk *clk;
 	struct regmap *regmap;
-	bool lvds_dual_link;
 	const struct fsl_ldb_devdata *devdata;
+	bool ch0_enabled;
+	bool ch1_enabled;
 };
 
+static bool fsl_ldb_is_dual(const struct fsl_ldb *fsl_ldb)
+{
+	return (fsl_ldb->ch0_enabled && fsl_ldb->ch1_enabled);
+}
+
 static inline struct fsl_ldb *to_fsl_ldb(struct drm_bridge *bridge)
 {
 	return container_of(bridge, struct fsl_ldb, bridge);
@@ -95,7 +101,7 @@ static inline struct fsl_ldb *to_fsl_ldb(struct drm_bridge *bridge)
 
 static unsigned long fsl_ldb_link_frequency(struct fsl_ldb *fsl_ldb, int clock)
 {
-	if (fsl_ldb->lvds_dual_link)
+	if (fsl_ldb_is_dual(fsl_ldb))
 		return clock * 3500;
 	else
 		return clock * 7000;
@@ -177,28 +183,21 @@ static void fsl_ldb_atomic_enable(struct drm_bridge *bridge,
 	clk_prepare_enable(fsl_ldb->clk);
 
 	/* Program LDB_CTRL */
-	reg = LDB_CTRL_CH0_ENABLE;
+	reg =	(fsl_ldb->ch0_enabled ? LDB_CTRL_CH0_ENABLE : 0) |
+		(fsl_ldb->ch1_enabled ? LDB_CTRL_CH1_ENABLE : 0) |
+		(fsl_ldb_is_dual(fsl_ldb) ? LDB_CTRL_SPLIT_MODE : 0);
 
-	if (fsl_ldb->lvds_dual_link)
-		reg |= LDB_CTRL_CH1_ENABLE | LDB_CTRL_SPLIT_MODE;
+	if (lvds_format_24bpp)
+		reg |=	(fsl_ldb->ch0_enabled ? LDB_CTRL_CH0_DATA_WIDTH : 0) |
+			(fsl_ldb->ch1_enabled ? LDB_CTRL_CH1_DATA_WIDTH : 0);
 
-	if (lvds_format_24bpp) {
-		reg |= LDB_CTRL_CH0_DATA_WIDTH;
-		if (fsl_ldb->lvds_dual_link)
-			reg |= LDB_CTRL_CH1_DATA_WIDTH;
-	}
+	if (lvds_format_jeida)
+		reg |=	(fsl_ldb->ch0_enabled ? LDB_CTRL_CH0_BIT_MAPPING : 0) |
+			(fsl_ldb->ch1_enabled ? LDB_CTRL_CH1_BIT_MAPPING : 0);
 
-	if (lvds_format_jeida) {
-		reg |= LDB_CTRL_CH0_BIT_MAPPING;
-		if (fsl_ldb->lvds_dual_link)
-			reg |= LDB_CTRL_CH1_BIT_MAPPING;
-	}
-
-	if (mode->flags & DRM_MODE_FLAG_PVSYNC) {
-		reg |= LDB_CTRL_DI0_VSYNC_POLARITY;
-		if (fsl_ldb->lvds_dual_link)
-			reg |= LDB_CTRL_DI1_VSYNC_POLARITY;
-	}
+	if (mode->flags & DRM_MODE_FLAG_PVSYNC)
+		reg |=	(fsl_ldb->ch0_enabled ? LDB_CTRL_DI0_VSYNC_POLARITY : 0) |
+			(fsl_ldb->ch1_enabled ? LDB_CTRL_DI1_VSYNC_POLARITY : 0);
 
 	regmap_write(fsl_ldb->regmap, fsl_ldb->devdata->ldb_ctrl, reg);
 
@@ -210,9 +209,8 @@ static void fsl_ldb_atomic_enable(struct drm_bridge *bridge,
 	/* Wait for VBG to stabilize. */
 	usleep_range(15, 20);
 
-	reg |= LVDS_CTRL_CH0_EN;
-	if (fsl_ldb->lvds_dual_link)
-		reg |= LVDS_CTRL_CH1_EN;
+	reg |=	(fsl_ldb->ch0_enabled ? LVDS_CTRL_CH0_EN : 0) |
+		(fsl_ldb->ch1_enabled ? LVDS_CTRL_CH1_EN : 0);
 
 	regmap_write(fsl_ldb->regmap, fsl_ldb->devdata->lvds_ctrl, reg);
 }
@@ -265,7 +263,7 @@ fsl_ldb_mode_valid(struct drm_bridge *bridge,
 {
 	struct fsl_ldb *fsl_ldb = to_fsl_ldb(bridge);
 
-	if (mode->clock > (fsl_ldb->lvds_dual_link ? 160000 : 80000))
+	if (mode->clock > (fsl_ldb_is_dual(fsl_ldb) ? 160000 : 80000))
 		return MODE_CLOCK_HIGH;
 
 	return MODE_OK;
@@ -286,7 +284,7 @@ static int fsl_ldb_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct device_node *panel_node;
-	struct device_node *port1, *port2;
+	struct device_node *remote1, *remote2;
 	struct drm_panel *panel;
 	struct fsl_ldb *fsl_ldb;
 	int dual_link;
@@ -311,10 +309,23 @@ static int fsl_ldb_probe(struct platform_device *pdev)
 	if (IS_ERR(fsl_ldb->regmap))
 		return PTR_ERR(fsl_ldb->regmap);
 
-	/* Locate the panel DT node. */
-	panel_node = of_graph_get_remote_node(dev->of_node, 1, 0);
-	if (!panel_node)
-		return -ENXIO;
+	/* Locate the remote ports and the panel node */
+	remote1 = of_graph_get_remote_node(dev->of_node, 1, 0);
+	remote2 = of_graph_get_remote_node(dev->of_node, 2, 0);
+	fsl_ldb->ch0_enabled = (remote1 != NULL);
+	fsl_ldb->ch1_enabled = (remote2 != NULL);
+	panel_node = of_node_get(remote1 ? remote1 : remote2);
+	of_node_put(remote1);
+	of_node_put(remote2);
+
+	if (!fsl_ldb->ch0_enabled && !fsl_ldb->ch1_enabled) {
+		of_node_put(panel_node);
+		return dev_err_probe(dev, -ENXIO, "No panel node found");
+	}
+
+	dev_dbg(dev, "Using %s\n",
+		fsl_ldb_is_dual(fsl_ldb) ? "dual-link mode" :
+		fsl_ldb->ch0_enabled ? "channel 0" : "channel 1");
 
 	panel = of_drm_find_panel(panel_node);
 	of_node_put(panel_node);
@@ -325,20 +336,26 @@ static int fsl_ldb_probe(struct platform_device *pdev)
 	if (IS_ERR(fsl_ldb->panel_bridge))
 		return PTR_ERR(fsl_ldb->panel_bridge);
 
-	/* Determine whether this is dual-link configuration */
+
+	if (fsl_ldb_is_dual(fsl_ldb)) {
+		struct device_node *port1, *port2;
+
 		port1 = of_graph_get_port_by_id(dev->of_node, 1);
 		port2 = of_graph_get_port_by_id(dev->of_node, 2);
 		dual_link = drm_of_lvds_get_dual_link_pixel_order(port1, port2);
 		of_node_put(port1);
 		of_node_put(port2);
 
+		if (dual_link < 0)
+			return dev_err_probe(dev, dual_link,
+					     "Error getting dual link configuration\n");
+
+		/* Only DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS is supported */
 		if (dual_link == DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS) {
 			dev_err(dev, "LVDS channel pixel swap not supported.\n");
 			return -EINVAL;
 		}
-
-	if (dual_link == DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS)
-		fsl_ldb->lvds_dual_link = true;
+	}
 
 	platform_set_drvdata(pdev, fsl_ldb);