drm: add of_graph endpoint helper to find possible CRTCs

Add a helper to allow encoders to find their possible CRTCs from the
OF graph without having to re-implement this functionality.  We add a
device_node to drm_crtc which corresponds with the port node in the
DT description of the CRTC device.

We can then scan the DRM device list for CRTCs to find their index,
matching the appropriate CRTC using the port device_node, thus building
up the possible CRTC mask.

Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

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);