drm/msm/dsi: parse vsync source from device tree

Allow board's device tree to specify the vsync source (aka TE source).
If the property is omitted, the display controller driver will use the
default setting.

Reviewed-by: Abhinav Kumar <[e-mail]>
[DB: fixed clearing of return value if there is no TE property]
Signed-off-by: Dmitry Baryshkov <[e-mail]>
Reviewed-by: Marijn Suijten <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/598740/
Link: https://lore.kernel.org/r/[e-mail]

drivers/gpu/drm/msm/dsi/dsi.h

···
 
 	struct mipi_dsi_host *host;
 	struct msm_dsi_phy *phy;
+	const char *te_source;
 
 	struct drm_bridge *next_bridge;
 

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

···
 
 static int dsi_host_parse_dt(struct msm_dsi_host *msm_host)
 {
+	struct msm_dsi *msm_dsi = platform_get_drvdata(msm_host->pdev);
 	struct device *dev = &msm_host->pdev->dev;
 	struct device_node *np = dev->of_node;
 	struct device_node *endpoint;
+	const char *te_source;
 	int ret = 0;
 
 	/*
···
 		ret = -EINVAL;
 		goto err;
 	}
+
+	ret = of_property_read_string(endpoint, "qcom,te-source", &te_source);
+	if (ret && ret != -EINVAL) {
+		DRM_DEV_ERROR(dev, "%s: invalid TE source configuration %d\n",
+			__func__, ret);
+		goto err;
+	}
+	if (!ret)
+		msm_dsi->te_source = devm_kstrdup(dev, te_source, GFP_KERNEL);
+	ret = 0;
 
 	if (of_property_read_bool(np, "syscon-sfpb")) {
 		msm_host->sfpb = syscon_regmap_lookup_by_phandle(np,

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

···
 {
 	return IS_MASTER_DSI_LINK(msm_dsi->id);
 }
+
+const char *msm_dsi_get_te_source(struct msm_dsi *msm_dsi)
+{
+	return msm_dsi->te_source;
+}

drivers/gpu/drm/msm/msm_drv.h

···
 bool msm_dsi_is_master_dsi(struct msm_dsi *msm_dsi);
 bool msm_dsi_wide_bus_enabled(struct msm_dsi *msm_dsi);
 struct drm_dsc_config *msm_dsi_get_dsc_config(struct msm_dsi *msm_dsi);
+const char *msm_dsi_get_te_source(struct msm_dsi *msm_dsi);
 #else
 static inline void __init msm_dsi_register(void)
 {
···
 }
 
 static inline struct drm_dsc_config *msm_dsi_get_dsc_config(struct msm_dsi *msm_dsi)
+{
+	return NULL;
+}
+
+static inline const char *msm_dsi_get_te_source(struct msm_dsi *msm_dsi)
 {
 	return NULL;
 }