Subject: Re: [PATCH v4 2/2] media: nxp: imx8-isi: Implement get_frame_desc for crossbar subdev

From: Laurent Pinchart <[email-masked]>
Date: Wed, 20 May 2026 23:22:01 +0200

Hello Guoniu,

Thank you for the patch.

On Fri, May 08, 2026 at 11:05:41AM +0800, Guoniu Zhou wrote:
> From: "Guoniu.zhou" <[email-masked]>
> 
> Implement the get_frame_desc pad operation for the crossbar subdevice
> to propagate frame descriptor information from the source subdevice to
> downstream ISI channels.
> 
> This allows the ISI driver to retrieve virtual channel information and
> other stream parameters from the connected upstream, which is required
> for proper virtual channel routing on platforms supporting multiple VCs.

Have you looked at v4l2_subdev_get_frame_desc_passthrough(), could it be
used instead of a manual implementation ? This could be either direct
usage of v4l2_subdev_get_frame_desc_passthrough(), or with minor
additional customization (first calling the unlocked helper
__v4l2_subdev_get_frame_desc_passthrough() and updating the descriptors.

> Signed-off-by: Guoniu.zhou <[email-masked]>
> ---
> Changes in v4:
> - Use %d instead of %u for ret variable in error messages
> - Fix potential -ENOIOCTLCMD leak by resetting ret to 0 on continue
> 
> Changes in v3:
> - New patch added based on feedback from Laurent Pinchart
> ---
>  .../platform/nxp/imx8-isi/imx8-isi-crossbar.c      | 98 ++++++++++++++++++++++
>  1 file changed, 98 insertions(+)
> 
> diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c b/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
> index 605a45124103..b5eff191b2d5 100644
> --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
> +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
> @@ -306,6 +306,103 @@ static int mxc_isi_crossbar_set_fmt(struct v4l2_subdev *sd,
>  	return 0;
>  }
>  
> +static int mxc_isi_get_frame_desc(struct v4l2_subdev *sd, unsigned int pad,
> +				  struct v4l2_mbus_frame_desc *fd)
> +{
> +	struct mxc_isi_crossbar *xbar = to_isi_crossbar(sd);
> +	struct device *dev = xbar->isi->dev;
> +	struct v4l2_subdev_route *route;
> +	struct v4l2_subdev_state *state;
> +	int ret = 0;
> +
> +	if (pad < xbar->num_sinks)
> +		return -EINVAL;
> +
> +	memset(fd, 0, sizeof(*fd));
> +
> +	state = v4l2_subdev_lock_and_get_active_state(sd);
> +
> +	/*
> +	 * Iterate over all active routes. For each route going through the
> +	 * requested source pad, get the frame descriptor from the connected
> +	 * source subdev, find the corresponding stream entry, and add it to
> +	 * the output frame descriptor with the routed stream ID.
> +	 */
> +	for_each_active_route(&state->routing, route) {
> +		struct v4l2_mbus_frame_desc source_fd;
> +		struct v4l2_subdev *remote_sd;
> +		struct media_pad *remote_pad;
> +		unsigned int i;
> +
> +		if (route->source_pad != pad)
> +			continue;
> +
> +		/* Find the remote subdev connected to this sink pad */
> +		remote_pad = media_pad_remote_pad_first(&xbar->pads[route->sink_pad]);
> +		if (!remote_pad) {
> +			dev_dbg(dev, "no remote pad connected to crossbar input %u\n",
> +				route->sink_pad);
> +			continue;
> +		}
> +
> +		remote_sd = media_entity_to_v4l2_subdev(remote_pad->entity);
> +		if (!remote_sd) {
> +			dev_err(dev, "no subdev connected to crossbar input %u\n",
> +				route->sink_pad);
> +			ret = -EPIPE;
> +			goto out_unlock;
> +		}
> +
> +		/* Get frame descriptor from the remote subdev */
> +		ret = v4l2_subdev_call(remote_sd, pad, get_frame_desc,
> +				       remote_pad->index, &source_fd);
> +		if (ret == -ENOIOCTLCMD) {
> +			dev_dbg(dev, "%s:%u does not support frame descriptors\n",
> +				remote_sd->entity.name, remote_pad->index);
> +			ret = 0;
> +			continue;
> +		}
> +		if (ret < 0) {
> +			dev_err(dev, "failed to get frame desc from %s:%u: %d\n",
> +				remote_sd->entity.name, remote_pad->index, ret);
> +			goto out_unlock;
> +		}
> +
> +		if (fd->num_entries == 0)
> +			fd->type = source_fd.type;
> +
> +		/* Find the source frame descriptor entry matching the sink stream */
> +		for (i = 0; i < source_fd.num_entries; i++) {
> +			if (source_fd.entry[i].stream == route->sink_stream)
> +				break;
> +		}
> +
> +		if (i == source_fd.num_entries) {
> +			dev_err(dev, "stream %u not found in frame desc from %s:%u\n",
> +				route->sink_stream, remote_sd->entity.name,
> +				remote_pad->index);
> +			ret = -EPIPE;
> +			goto out_unlock;
> +		}
> +
> +		if (fd->num_entries >= ARRAY_SIZE(fd->entry)) {
> +			dev_err(dev, "frame descriptor is full\n");
> +			ret = -ENOSPC;
> +			goto out_unlock;
> +		}
> +
> +		/* Copy the entry and update the stream ID */
> +		fd->entry[fd->num_entries] = source_fd.entry[i];
> +		fd->entry[fd->num_entries].stream = route->source_stream;
> +		fd->num_entries++;
> +	}
> +
> +out_unlock:
> +	v4l2_subdev_unlock_state(state);
> +
> +	return ret;
> +}
> +
>  static int mxc_isi_crossbar_set_routing(struct v4l2_subdev *sd,
>  					struct v4l2_subdev_state *state,
>  					enum v4l2_subdev_format_whence which,
> @@ -404,6 +501,7 @@ static const struct v4l2_subdev_pad_ops mxc_isi_crossbar_subdev_pad_ops = {
>  	.enum_mbus_code = mxc_isi_crossbar_enum_mbus_code,
>  	.get_fmt = v4l2_subdev_get_fmt,
>  	.set_fmt = mxc_isi_crossbar_set_fmt,
> +	.get_frame_desc = mxc_isi_get_frame_desc,
>  	.set_routing = mxc_isi_crossbar_set_routing,
>  	.enable_streams = mxc_isi_crossbar_enable_streams,
>  	.disable_streams = mxc_isi_crossbar_disable_streams,

-- 
Regards,

Laurent Pinchart