drm/panel: Make of_drm_find_panel() return an ERR_PTR() instead of NULL

Right now, the DRM panel logic returns NULL when a panel pointing to
the passed OF node is not present in the list of registered panels.

Most drivers interpret this NULL value as -EPROBE_DEFER, but we are
about to modify the semantic of of_drm_find_panel() and let the
framework return -ENODEV when the device node we're pointing to has
a status property that is not equal to "okay" or "ok".

Let's first patch the of_drm_find_panel() implementation to return
ERR_PTR(-EPROBE_DEFER) instead of NULL and patch all callers to replace
the '!panel' check by an 'IS_ERR(panel)' one.
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180509130042.9435-2-boris.brezillon@bootlin.com

drivers/gpu/drm/bridge/cdns-dsi.c

@@ -1152,7 +1152,7 @@ static int cdns_dsi_attach(struct mipi_dsi_host *host,
 		np = of_node_get(dev->dev.of_node);
 
 	panel = of_drm_find_panel(np);
-	if (panel) {
+	if (!IS_ERR(panel)) {
 		bridge = drm_panel_bridge_add(panel, DRM_MODE_CONNECTOR_DSI);
 	} else {
 		bridge = of_drm_find_bridge(dev->dev.of_node);

drivers/gpu/drm/bridge/lvds-encoder.c

@@ -68,9 +68,9 @@ static int lvds_encoder_probe(struct platform_device *pdev)
 
 	panel = of_drm_find_panel(panel_node);
 	of_node_put(panel_node);
-	if (!panel) {
+	if (IS_ERR(panel)) {
 		dev_dbg(&pdev->dev, "panel not found, deferring probe\n");
-		return -EPROBE_DEFER;
+		return PTR_ERR(panel);
 	}
 
 	lvds_encoder->panel_bridge =

drivers/gpu/drm/drm_of.c

@@ -241,8 +241,10 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
 
 	if (panel) {
 		*panel = of_drm_find_panel(remote);
-		if (*panel)
+		if (!IS_ERR(*panel))
 			ret = 0;
+		else
+			*panel = NULL;
 	}
 
 	/* No panel found yet, check for a bridge next. */

drivers/gpu/drm/drm_panel.c

@@ -151,7 +151,9 @@ EXPORT_SYMBOL(drm_panel_detach);
  * tree node. If a matching panel is found, return a pointer to it.
  *
  * Return: A pointer to the panel registered for the specified device tree
- * node or NULL if no panel matching the device tree node can be found.
+ * node or an ERR_PTR() if no panel matching the device tree node can be found.
+ * The only error that can be reported is -EPROBE_DEFER, meaning that the panel
+ * device has not been probed yet, and the caller should retry later.
  */
 struct drm_panel *of_drm_find_panel(const struct device_node *np)
 {
@@ -167,7 +169,7 @@ struct drm_panel *of_drm_find_panel(const struct device_node *np)
 	}
 
 	mutex_unlock(&panel_lock);
-	return NULL;
+	return ERR_PTR(-EPROBE_DEFER);
 }
 EXPORT_SYMBOL(of_drm_find_panel);
 #endif

drivers/gpu/drm/exynos/exynos_dp.c

@@ -232,9 +232,11 @@ static int exynos_dp_probe(struct platform_device *pdev)
 	np = of_parse_phandle(dev->of_node, "panel", 0);
 	if (np) {
 		dp->plat_data.panel = of_drm_find_panel(np);
+
 		of_node_put(np);
-		if (!dp->plat_data.panel)
-			return -EPROBE_DEFER;
+		if (IS_ERR(dp->plat_data.panel))
+			return PTR_ERR(dp->plat_data.panel);
+
 		goto out;
 	}
 

drivers/gpu/drm/exynos/exynos_drm_dpi.c

@@ -240,8 +240,8 @@ struct drm_encoder *exynos_dpi_probe(struct device *dev)
 
 	if (ctx->panel_node) {
 		ctx->panel = of_drm_find_panel(ctx->panel_node);
-		if (!ctx->panel)
-			return ERR_PTR(-EPROBE_DEFER);
+		if (IS_ERR(ctx->panel))
+			return ERR_CAST(ctx->panel);
 	}
 
 	return &ctx->encoder;

drivers/gpu/drm/exynos/exynos_drm_dsi.c

@@ -1519,6 +1519,9 @@ static int exynos_dsi_host_attach(struct mipi_dsi_host *host,
 	dsi->format = device->format;
 	dsi->mode_flags = device->mode_flags;
 	dsi->panel = of_drm_find_panel(device->dev.of_node);
+	if (IS_ERR(dsi->panel))
+		dsi->panel = NULL;
+
 	if (dsi->panel) {
 		drm_panel_attach(dsi->panel, &dsi->connector);
 		dsi->connector.status = connector_status_connected;

drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c

@@ -148,8 +148,9 @@ int fsl_dcu_create_outputs(struct fsl_dcu_drm_device *fsl_dev)
 	if (panel_node) {
 		fsl_dev->connector.panel = of_drm_find_panel(panel_node);
 		of_node_put(panel_node);
-		if (!fsl_dev->connector.panel)
-			return -EPROBE_DEFER;
+		if (IS_ERR(fsl_dev->connector.panel))
+			return PTR_ERR(fsl_dev->connector.panel);
+
 		return fsl_dcu_attach_panel(fsl_dev, fsl_dev->connector.panel);
 	}
 

drivers/gpu/drm/msm/disp/mdp4/mdp4_lcdc_encoder.c

@@ -341,7 +341,7 @@ static void mdp4_lcdc_encoder_disable(struct drm_encoder *encoder)
 	mdp4_write(mdp4_kms, REG_MDP4_LCDC_ENABLE, 0);
 
 	panel = of_drm_find_panel(mdp4_lcdc_encoder->panel_node);
-	if (panel) {
+	if (!IS_ERR(panel)) {
 		drm_panel_disable(panel);
 		drm_panel_unprepare(panel);
 	}
@@ -410,7 +410,7 @@ static void mdp4_lcdc_encoder_enable(struct drm_encoder *encoder)
 		dev_err(dev->dev, "failed to enable lcdc_clk: %d\n", ret);
 
 	panel = of_drm_find_panel(mdp4_lcdc_encoder->panel_node);
-	if (panel) {
+	if (!IS_ERR(panel)) {
 		drm_panel_prepare(panel);
 		drm_panel_enable(panel);
 	}

drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c

@@ -34,9 +34,12 @@ static enum drm_connector_status mdp4_lvds_connector_detect(
 	struct mdp4_lvds_connector *mdp4_lvds_connector =
 			to_mdp4_lvds_connector(connector);
 
-	if (!mdp4_lvds_connector->panel)
+	if (!mdp4_lvds_connector->panel) {
 		mdp4_lvds_connector->panel =
 			of_drm_find_panel(mdp4_lvds_connector->panel_node);
+		if (IS_ERR(mdp4_lvds_connector->panel))
+			mdp4_lvds_connector->panel = NULL;
+	}
 
 	return mdp4_lvds_connector->panel ?
 			connector_status_connected :

drivers/gpu/drm/msm/dsi/dsi_host.c

@@ -1898,7 +1898,7 @@ int msm_dsi_host_register(struct mipi_dsi_host *host, bool check_defer)
 		 * output
 		 */
 		if (check_defer && msm_host->device_node) {
-			if (!of_drm_find_panel(msm_host->device_node))
+			if (IS_ERR(of_drm_find_panel(msm_host->device_node)))
 				if (!of_drm_find_bridge(msm_host->device_node))
 					return -EPROBE_DEFER;
 		}

drivers/gpu/drm/rcar-du/rcar_lvds.c

@@ -434,8 +434,8 @@ static int rcar_lvds_parse_dt(struct rcar_lvds *lvds)
 			ret = -EPROBE_DEFER;
 	} else {
 		lvds->panel = of_drm_find_panel(remote);
-		if (!lvds->panel)
-			ret = -EPROBE_DEFER;
+		if (IS_ERR(lvds->panel))
+			ret = PTR_ERR(lvds->panel);
 	}
 
 done:

drivers/gpu/drm/rockchip/dw-mipi-dsi.c

@@ -595,7 +595,7 @@ static int dw_mipi_dsi_host_attach(struct mipi_dsi_host *host,
 	dsi->format = device->format;
 	dsi->mode_flags = device->mode_flags;
 	dsi->panel = of_drm_find_panel(device->dev.of_node);
-	if (dsi->panel)
+	if (!IS_ERR(dsi->panel))
 		return drm_panel_attach(dsi->panel, &dsi->connector);
 
 	return -EINVAL;

drivers/gpu/drm/sti/sti_dvo.c

@@ -387,7 +387,9 @@ sti_dvo_connector_detect(struct drm_connector *connector, bool force)
 
 	if (!dvo->panel) {
 		dvo->panel = of_drm_find_panel(dvo->panel_node);
-		if (dvo->panel)
+		if (IS_ERR(dvo->panel))
+			dvo->panel = NULL;
+		else
 			drm_panel_attach(dvo->panel, connector);
 	}
 

drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c

@@ -833,8 +833,8 @@ static int sun6i_dsi_attach(struct mipi_dsi_host *host,
 
 	dsi->device = device;
 	dsi->panel = of_drm_find_panel(device->dev.of_node);
-	if (!dsi->panel)
-		return -EINVAL;
+	if (IS_ERR(dsi->panel))
+		return PTR_ERR(dsi->panel);
 
 	dev_info(host->dev, "Attached device %s\n", device->name);
 

drivers/gpu/drm/tegra/dsi.c

@@ -1411,6 +1411,9 @@ static int tegra_dsi_host_attach(struct mipi_dsi_host *host,
 		struct tegra_output *output = &dsi->output;
 
 		output->panel = of_drm_find_panel(device->dev.of_node);
+		if (IS_ERR(output->panel))
+			output->panel = NULL;
+
 		if (output->panel && output->connector.dev) {
 			drm_panel_attach(output->panel, &output->connector);
 			drm_helper_hpd_irq_event(output->connector.dev);

drivers/gpu/drm/tegra/output.c

@@ -110,8 +110,8 @@ int tegra_output_probe(struct tegra_output *output)
 	panel = of_parse_phandle(output->of_node, "nvidia,panel", 0);
 	if (panel) {
 		output->panel = of_drm_find_panel(panel);
-		if (!output->panel)
-			return -EPROBE_DEFER;
+		if (IS_ERR(output->panel))
+			return PTR_ERR(output->panel);
 
 		of_node_put(panel);
 	}

include/drm/drm_panel.h

@@ -200,7 +200,7 @@ struct drm_panel *of_drm_find_panel(const struct device_node *np);
 #else
 static inline struct drm_panel *of_drm_find_panel(const struct device_node *np)
 {
-	return NULL;
+	return ERR_PTR(-ENODEV);
 }
 #endif