Add a helper for v4l2_subdev_pad_ops.get_frame_desc operation. The
helper can be used when the subdevice directly passes through the
streams.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
---
 drivers/media/v4l2-core/v4l2-subdev.c | 111 ++++++++++++++++++++++++++++++++++
 include/media/v4l2-subdev.h           |  28 +++++++++
 2 files changed, 139 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index 32e6f60e26c7..2757378c628a 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -2545,6 +2545,117 @@ int v4l2_subdev_s_stream_helper(struct v4l2_subdev *sd, int enable)
 }
 EXPORT_SYMBOL_GPL(v4l2_subdev_s_stream_helper);
 
+int v4l2_subdev_get_frame_desc_passthrough(struct v4l2_subdev *sd,
+					   unsigned int pad,
+					   struct v4l2_mbus_frame_desc *fd)
+{
+	struct media_pad *local_sink_pad;
+	struct v4l2_subdev_route *route;
+	struct v4l2_subdev_state *state;
+	struct device *dev = sd->dev;
+	int ret = 0;
+
+	if (WARN_ON(!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE)))
+		return -EINVAL;
+
+	state = v4l2_subdev_lock_and_get_active_state(sd);
+
+	/* Iterate over sink pads */
+	media_entity_for_each_pad(&sd->entity, local_sink_pad) {
+		struct v4l2_mbus_frame_desc source_fd;
+		bool have_source_fd = false;
+
+		if (!(local_sink_pad->flags & MEDIA_PAD_FL_SINK))
+			continue;
+
+		/*
+		 * Copy frame desc entries for the streams going from the sink
+		 * pad to the requested pad
+		 */
+		for_each_active_route(&state->routing, route) {
+			struct v4l2_mbus_frame_desc_entry *source_entry = NULL;
+			struct media_pad *remote_source_pad;
+			struct v4l2_subdev *remote_sd;
+
+			if (route->source_pad != pad ||
+			    route->sink_pad != local_sink_pad->index)
+				continue;
+
+			if (!have_source_fd) {
+				remote_source_pad = media_pad_remote_pad_unique(local_sink_pad);
+				if (!remote_source_pad) {
+					dev_dbg(dev, "Failed to find remote pad for sink pad %u\n",
+						local_sink_pad->index);
+					ret = -EINVAL;
+					goto out_unlock;
+				}
+
+				remote_sd = media_entity_to_v4l2_subdev(remote_source_pad->entity);
+				if (!remote_sd) {
+					ret = -EINVAL;
+					goto out_unlock;
+				}
+
+				ret = v4l2_subdev_call(remote_sd, pad,
+						       get_frame_desc,
+						       remote_source_pad->index,
+						       &source_fd);
+				if (ret) {
+					dev_err(dev,
+						"Failed to get frame desc from remote subdev %s\n",
+						remote_sd->name);
+					goto out_unlock;
+				}
+
+				have_source_fd = true;
+
+				if (fd->num_entries == 0) {
+					fd->type = source_fd.type;
+				} else if (fd->type != source_fd.type) {
+					dev_err(dev,
+						"Frame desc type mismatch: %u != %u\n",
+						fd->type, source_fd.type);
+					ret = -EPIPE;
+					goto out_unlock;
+				}
+			}
+
+			for (unsigned int i = 0; i < source_fd.num_entries; i++) {
+				if (source_fd.entry[i].stream == route->sink_stream) {
+					source_entry = &source_fd.entry[i];
+					break;
+				}
+			}
+
+			if (!source_entry) {
+				dev_dbg(dev,
+					"Failed to find stream %u from source frame desc\n",
+					route->sink_stream);
+				ret = -EPIPE;
+				goto out_unlock;
+			}
+
+			if (fd->num_entries >= V4L2_FRAME_DESC_ENTRY_MAX) {
+				dev_dbg(dev, "Frame desc entry limit reached\n");
+				ret = -ENOSPC;
+				goto out_unlock;
+			}
+
+			fd->entry[fd->num_entries] = *source_entry;
+
+			fd->entry[fd->num_entries].stream = route->source_stream;
+
+			fd->num_entries++;
+		}
+	}
+
+out_unlock:
+	v4l2_subdev_unlock_state(state);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(v4l2_subdev_get_frame_desc_passthrough);
+
 #endif /* CONFIG_VIDEO_V4L2_SUBDEV_API */
 
 #endif /* CONFIG_MEDIA_CONTROLLER */
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index a37d9a847196..23c03ba7f84c 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -1722,6 +1722,34 @@ int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
  */
 int v4l2_subdev_s_stream_helper(struct v4l2_subdev *sd, int enable);
 
+/**
+ * v4l2_subdev_get_frame_desc_passthrough() - Helper to implement the subdev
+ *	get_frame_desc operation in simple passthrough cases
+ * @sd: The subdevice
+ * @pad: The source pad index
+ * @fd: The mbus frame desc
+ *
+ * This helper implements get_frame_desc operation for subdevices that pass
+ * streams through without modification. It can be assigned directly as the
+ * .get_frame_desc callback in &v4l2_subdev_pad_ops.
+ *
+ * The helper iterates over the subdevice's sink pads, calls get_frame_desc on
+ * the remote subdevice connected to each sink pad, and collects the frame desc
+ * entries for streams that are routed to the given source pad according to the
+ * subdevice's routing table. Each entry is copied as-is from the upstream
+ * source, with the exception of the 'stream' field which is remapped to the
+ * source stream ID from the routing table.
+ *
+ * The frame desc type is taken from the first upstream source. If multiple
+ * sink pads are involved and the upstream sources report different frame desc
+ * types, -EPIPE is returned.
+ *
+ * Return: 0 on success, or a negative error code otherwise.
+ */
+int v4l2_subdev_get_frame_desc_passthrough(struct v4l2_subdev *sd,
+					   unsigned int pad,
+					   struct v4l2_mbus_frame_desc *fd);
+
 #endif /* CONFIG_VIDEO_V4L2_SUBDEV_API */
 
 #endif /* CONFIG_MEDIA_CONTROLLER */

-- 
2.43.0