Re: [PATCH v4 24/29] media: v4l2-subdev: Introduce v4l2_subdev_get_frame_desc()

Jacopo Mondi
2026-04-10T10:53:48Z

Hi Sakari

On Wed, Apr 08, 2026 at 06:39:33PM +0300, Sakari Ailus wrote:
> Introduce v4l2_subdev_get_frame_desc() in order to facilitate implementing
> drivers that need frame descriptors. If the remote sub-device does not
> support frame descriptors, v4l2_subdev_get_frame_desc() creates one (with
> a single entry) opportunistically, thus avoiding the need to add frame
> descriptor support to sensor drivers the device for which only generates a
> single stream, or managing the situation on the caller side.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
> drivers/media/v4l2-core/v4l2-subdev.c | 96 +++++++++++++++++++++++++++
> include/media/v4l2-subdev.h | 20 ++++++
> 2 files changed, 116 insertions(+)
>
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index 647587c0499a..40b28e070726 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -20,6 +20,7 @@
> #include <linux/version.h>
> #include <linux/videodev2.h>
>
> +#include <media/mipi-csi2.h>
> #include <media/v4l2-ctrls.h>
> #include <media/v4l2-device.h>
> #include <media/v4l2-event.h>
> @@ -2758,3 +2759,98 @@ void v4l2_subdev_put_privacy_led(struct v4l2_subdev *sd)
> #endif
> }
> EXPORT_SYMBOL_GPL(v4l2_subdev_put_privacy_led);
> +
> +static int get_mipi_dt_for_mbus(u32 code)
> +{
> + switch (code) {
> + case MEDIA_BUS_FMT_BGR888_1X24:
> + return MIPI_CSI2_DT_RGB888;
> + case MEDIA_BUS_FMT_Y8_1X8:
> + case MEDIA_BUS_FMT_SBGGR8_1X8:
> + case MEDIA_BUS_FMT_SGBRG8_1X8:
> + case MEDIA_BUS_FMT_SGRBG8_1X8:
> + case MEDIA_BUS_FMT_SRGGB8_1X8:
> + return MIPI_CSI2_DT_RAW8;
> + case MEDIA_BUS_FMT_Y10_1X10:
> + case MEDIA_BUS_FMT_SBGGR10_1X10:
> + case MEDIA_BUS_FMT_SGBRG10_1X10:
> + case MEDIA_BUS_FMT_SGRBG10_1X10:
> + case MEDIA_BUS_FMT_SRGGB10_1X10:
> + return MIPI_CSI2_DT_RAW10;
> + case MEDIA_BUS_FMT_Y12_1X12:
> + case MEDIA_BUS_FMT_SBGGR12_1X12:
> + case MEDIA_BUS_FMT_SGBRG12_1X12:
> + case MEDIA_BUS_FMT_SGRBG12_1X12:
> + case MEDIA_BUS_FMT_SRGGB12_1X12:
> + return MIPI_CSI2_DT_RAW12;
> + case MEDIA_BUS_FMT_Y14_1X14:
> + case MEDIA_BUS_FMT_SBGGR14_1X14:
> + case MEDIA_BUS_FMT_SGBRG14_1X14:
> + case MEDIA_BUS_FMT_SGRBG14_1X14:
> + case MEDIA_BUS_FMT_SRGGB14_1X14:
> + return MIPI_CSI2_DT_RAW14;
> + case MEDIA_BUS_FMT_Y16_1X16:
> + case MEDIA_BUS_FMT_SBGGR16_1X16:
> + case MEDIA_BUS_FMT_SGBRG16_1X16:
> + case MEDIA_BUS_FMT_SGRBG16_1X16:
> + case MEDIA_BUS_FMT_SRGGB16_1X16:
> + return MIPI_CSI2_DT_RAW16;
> + case MEDIA_BUS_FMT_SBGGR20_1X20:
> + case MEDIA_BUS_FMT_SGBRG20_1X20:
> + case MEDIA_BUS_FMT_SGRBG20_1X20:
> + case MEDIA_BUS_FMT_SRGGB20_1X20:
> + return MIPI_CSI2_DT_RAW20;
> + default:
> + return -EINVAL;
> + }
> +}
> +
> +int v4l2_subdev_get_frame_desc(struct v4l2_subdev *sd, unsigned int pad,
> + struct v4l2_mbus_frame_desc *desc)
> +{
> + struct v4l2_subdev_format subdev_fmt = {
> + .which = V4L2_SUBDEV_FORMAT_ACTIVE,
> + .pad = pad,
> + };
> + int ret;
> +
> + if (v4l2_subdev_has_op(sd, pad, get_frame_desc)) {
> + unsigned int type = desc->type;
> +
> + ret = v4l2_subdev_call(sd, pad, get_frame_desc, pad, desc);
> +
> + if (desc->type != type)
> + return -EINVAL;
> +
> + return ret;
> + }
> +
> + if (desc->type != V4L2_MBUS_FRAME_DESC_TYPE_PARALLEL &&
> + desc->type != V4L2_MBUS_FRAME_DESC_TYPE_CSI2)
> + return -EINVAL;
> +
> + ret = v4l2_subdev_call(sd, pad, get_fmt, NULL, NULL,
> + &subdev_fmt);
> + if (ret)
> + return ret;
> +
> + struct v4l2_mbus_frame_desc_entry entry = {
> + .pixelcode = subdev_fmt.format.code,
> + };
> +
> + if (desc->type == V4L2_MBUS_FRAME_DESC_TYPE_CSI2) {
> + int dt;
> +
> + dt = get_mipi_dt_for_mbus(subdev_fmt.format.code);
> + if (dt < 0)
> + return dt;
> +
> + entry.bus.csi2.dt = dt;
> + }
> +
> + desc->entry[0] = entry;
> + desc->num_entries = 1;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_subdev_get_frame_desc);
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index 4588992b4417..93b672edd08e 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -2058,4 +2058,24 @@ void v4l2_subdev_notify_event(struct v4l2_subdev *sd,
> */
> bool v4l2_subdev_is_streaming(struct v4l2_subdev *sd);
>
> +/**
> + * v4l2_subdev_get_frame_desc() - Get a pad's frame descriptor
> + * @sd: The sub-device
> + * @pad: The number of the pad in @sd from which to obtain the frame descriptor
> + * @desc: A pointer to a frame descriptor, with its type field set
> + *
> + * Obtain a frame descriptor from a sub-device. If the sub-device supports the
> + * get_frame_desc pad operation, its result is returned, just like calling it
> + * directly using v4l2_subdev_call(). If the sub-device driver does not support
> + * it, then one containing a single entry is created using the information from
> + * the sub-device active state, which this function locks for the duration of
> + * the call to obtain it.

This doesn't seem to apply anymore...

> + *
> + * The caller is required to set @desc->type to the expected bus type.

Is it worth mentioning that only V4L2_MBUS_FRAME_DESC_TYPE_PARALLEL
and V4L2_MBUS_FRAME_DESC_TYPE_CSI2 are supported ?

> + *
> + * Return: %0 on success or negative error code on failure.
> + */
> +int v4l2_subdev_get_frame_desc(struct v4l2_subdev *sd, unsigned int pad,
> + struct v4l2_mbus_frame_desc *desc);

With the documentation addressed
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

Thanks
j

> +
> #endif /* _V4L2_SUBDEV_H */
> --
> 2.47.3
>
>