1 files changed, 67 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
new file mode 100644
index 000000000000..16150a00c237
--- /dev/null
+++ b/drivers/gpu/drm/drm_of.c
@@ -0,0 +1,67 @@
+#include <linux/export.h>
+#include <linux/list.h>
+#include <linux/of_graph.h>
+#include <drm/drmP.h>
+#include <drm/drm_crtc.h>
+#include <drm/drm_of.h>
+
+/**
+ * drm_crtc_port_mask - find the mask of a registered CRTC by port OF node
+ * @dev: DRM device
+ * @port: port OF node
+ *
+ * Given a port OF node, return the possible mask of the corresponding
+ * CRTC within a device's list of CRTCs.  Returns zero if not found.
+ */
+static uint32_t drm_crtc_port_mask(struct drm_device *dev,
+				   struct device_node *port)
+{
+	unsigned int index = 0;
+	struct drm_crtc *tmp;
+
+	list_for_each_entry(tmp, &dev->mode_config.crtc_list, head) {
+		if (tmp->port == port)
+			return 1 << index;
+
+		index++;
+	}
+
+	return 0;
+}
+
+/**
+ * drm_of_find_possible_crtcs - find the possible CRTCs for an encoder port
+ * @dev: DRM device
+ * @port: encoder port to scan for endpoints
+ *
+ * Scan all endpoints attached to a port, locate their attached CRTCs,
+ * and generate the DRM mask of CRTCs which may be attached to this
+ * encoder.
+ *
+ * See Documentation/devicetree/bindings/graph.txt for the bindings.
+ */
+uint32_t drm_of_find_possible_crtcs(struct drm_device *dev,
+				    struct device_node *port)
+{
+	struct device_node *remote_port, *ep = NULL;
+	uint32_t possible_crtcs = 0;
+
+	do {
+		ep = of_graph_get_next_endpoint(port, ep);
+		if (!ep)
+			break;
+
+		remote_port = of_graph_get_remote_port(ep);
+		if (!remote_port) {
+			of_node_put(ep);
+			return 0;
+		}
+
+		possible_crtcs |= drm_crtc_port_mask(dev, remote_port);
+
+		of_node_put(remote_port);
+	} while (1);
+
+	return possible_crtcs;
+}
+EXPORT_SYMBOL(drm_of_find_possible_crtcs);