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

Sakari Ailus
2026-04-13T08:06:57Z

Hi Jacopo,

Thank you for the review.

On Fri, Apr 10, 2026 at 12:53:42PM +0200, Jacopo Mondi wrote:
> 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...

I'll rephrase it.

>
> > + *
> > + * 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 ?

I'll add that.

>
>
> > + *
> > + * 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!

--
Kind regards,

Sakari Ailus