2 files changed, 68 insertions, 0 deletions

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index dd2ba4269740..533d011eab3e 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -20,6 +20,7 @@ drm-$(CONFIG_COMPAT) += drm_ioc32.o
 drm-$(CONFIG_DRM_GEM_CMA_HELPER) += drm_gem_cma_helper.o
 drm-$(CONFIG_PCI) += ati_pcigart.o
 drm-$(CONFIG_DRM_PANEL) += drm_panel.o
+drm-$(CONFIG_OF) += drm_of.o
 
 drm-usb-y   := drm_usb.o
 
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);