drm: of: Add drm_of_get_data_lanes_count and drm_of_get_data_lanes_ep

Add helper function to count and sanitize DT "data-lanes" property
and return either error or the data-lanes count. This is useful for
both DSI and (e)DP "data-lanes" property. The later version of the
function is an extra wrapper which handles the endpoint look up by
regs, that's what majority of the drivers duplicate too, but not all
of them.
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
To: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20220524010522.528569-1-marex@denx.de

drivers/gpu/drm/drm_of.c

@@ -430,3 +430,64 @@ int drm_of_lvds_get_data_mapping(const struct device_node *port)
 	return -EINVAL;
 }
 EXPORT_SYMBOL_GPL(drm_of_lvds_get_data_mapping);
+
+/**
+ * drm_of_get_data_lanes_count - Get DSI/(e)DP data lane count
+ * @endpoint: DT endpoint node of the DSI/(e)DP source or sink
+ * @min: minimum supported number of data lanes
+ * @max: maximum supported number of data lanes
+ *
+ * Count DT "data-lanes" property elements and check for validity.
+ *
+ * Return:
+ * * min..max - positive integer count of "data-lanes" elements
+ * * -ve - the "data-lanes" property is missing or invalid
+ * * -EINVAL - the "data-lanes" property is unsupported
+ */
+int drm_of_get_data_lanes_count(const struct device_node *endpoint,
+				const unsigned int min, const unsigned int max)
+{
+	int ret;
+
+	ret = of_property_count_u32_elems(endpoint, "data-lanes");
+	if (ret < 0)
+		return ret;
+
+	if (ret < min || ret > max)
+		return -EINVAL;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(drm_of_get_data_lanes_count);
+
+/**
+ * drm_of_get_data_lanes_count_ep - Get DSI/(e)DP data lane count by endpoint
+ * @port: DT port node of the DSI/(e)DP source or sink
+ * @port_reg: identifier (value of reg property) of the parent port node
+ * @reg: identifier (value of reg property) of the endpoint node
+ * @min: minimum supported number of data lanes
+ * @max: maximum supported number of data lanes
+ *
+ * Count DT "data-lanes" property elements and check for validity.
+ * This variant uses endpoint specifier.
+ *
+ * Return:
+ * * min..max - positive integer count of "data-lanes" elements
+ * * -EINVAL - the "data-mapping" property is unsupported
+ * * -ENODEV - the "data-mapping" property is missing
+ */
+int drm_of_get_data_lanes_count_ep(const struct device_node *port,
+				   int port_reg, int reg,
+				   const unsigned int min,
+				   const unsigned int max)
+{
+	struct device_node *endpoint;
+	int ret;
+
+	endpoint = of_graph_get_endpoint_by_regs(port, port_reg, reg);
+	ret = drm_of_get_data_lanes_count(endpoint, min, max);
+	of_node_put(endpoint);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(drm_of_get_data_lanes_count_ep);

include/drm/drm_of.h

@@ -50,6 +50,12 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
 int drm_of_lvds_get_dual_link_pixel_order(const struct device_node *port1,
 					  const struct device_node *port2);
 int drm_of_lvds_get_data_mapping(const struct device_node *port);
+int drm_of_get_data_lanes_count(const struct device_node *endpoint,
+				const unsigned int min, const unsigned int max);
+int drm_of_get_data_lanes_count_ep(const struct device_node *port,
+				   int port_reg, int reg,
+				   const unsigned int min,
+				   const unsigned int max);
 #else
 static inline uint32_t drm_of_crtc_port_mask(struct drm_device *dev,
 					  struct device_node *port)
@@ -105,6 +111,20 @@ drm_of_lvds_get_data_mapping(const struct device_node *port)
 {
 	return -EINVAL;
 }
+
+int drm_of_get_data_lanes_count(const struct device_node *endpoint,
+				const unsigned int min, const unsigned int max)
+{
+	return -EINVAL;
+}
+
+int drm_of_get_data_lanes_count_ep(const struct device_node *port,
+				   int port_reg, int reg
+				   const unsigned int min,
+				   const unsigned int max)
+{
+	return -EINVAL;
+}
 #endif
 
 /*