Re: [PATCH v3 1/2] media: videodev2: Add flags to unconditionnaly enumerate pixels formats

[Jacopo Mondi]

Hi Benjamin

On Fri, Jul 12, 2024 at 12:29:59PM GMT, Benjamin Gaignard wrote:
> Add new flags to enumerate all pixels formats when calling VIDIOC_ENUM_FMT ioctl.
> When this V4L2_FMT_FLAG_ENUM_ALL_FORMATS flag is set drivers must
> ignore the configuration and return the hardware supported pixel
> formats for the specified queue.
> To distinguish this particular enumeration case V4L2_FMT_FLAG_ALL_FORMATS
> flag must be set by the drivers to highlight support of this feature
> to user space applications.
> This will permit to discover which pixel formats are supported
> without setting codec-specific information so userland can more easily
> know if the driver suits its needs well.
> The main target are stateless decoders so update the documentation
> about how to use this flag.
>
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> ---
> changes in version 3:
> - Add a flag to inform userspace application that driver
>   as take care of the flag.
>
>  .../userspace-api/media/v4l/dev-stateless-decoder.rst    | 6 ++++++
>  .../userspace-api/media/v4l/vidioc-enum-fmt.rst          | 9 +++++++++
>  .../userspace-api/media/videodev2.h.rst.exceptions       | 2 ++
>  drivers/media/v4l2-core/v4l2-ioctl.c                     | 3 +++
>  include/uapi/linux/videodev2.h                           | 2 ++
>  5 files changed, 22 insertions(+)
>
> diff --git a/Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst b/Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst
> index 35ed05f2695e..b0b657de910d 100644
> --- a/Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst
> +++ b/Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst
> @@ -58,6 +58,12 @@ Querying capabilities
>       default values for these controls being used, and a returned set of formats
>       that may not be usable for the media the client is trying to decode.
>
> +   * If the ``V4L2_FMT_FLAG_ENUM_ALL_FORMATS`` flag is set the driver must enumerate
> +     all the supported formats without taking care of codec-dependent controls
> +     set on the ``OUTPUT`` queue. To indicate that the driver has take care of this
> +     flag it must set ``V4L2_FMT_FLAG_ALL_FORMATS`` flag for each format while
> +     enumerating.
> +
>  3. The client may use :c:func:`VIDIOC_ENUM_FRAMESIZES` to detect supported
>     resolutions for a given format, passing desired pixel format in
>     :c:type:`v4l2_frmsizeenum`'s ``pixel_format``.
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
> index 3adb3d205531..0399e0fc09b3 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
> @@ -234,6 +234,15 @@ the ``mbus_code`` field is handled differently:
>  	valid. The buffer consists of ``height`` lines, each having ``width``
>  	Data Units of data and the offset (in bytes) between the beginning of
>  	each two consecutive lines is ``bytesperline``.
> +    * - ``V4L2_FMT_FLAG_ENUM_ALL_FORMATS``
> +      - 0x0400
> +      - Set by userland applications to enumerate all possible pixel formats
> +        without taking care of any OUTPUT or CAPTURE queue configuration.

This seems to be only relevant for codecs and m2m devices.

For 'regular' capture (and I presume output) devices isn't the default
behaviour to enumerate all pixel formats, and userspace can decide to
restrict them by providing a media bus code (if the device reports the
V4L2_CAP_IO_MC capability)


> +    * - ``V4L2_FMT_FLAG_ALL_FORMATS``
> +      - 0x0800
> +      - Set by the driver to indicated that format have been enumerated because
> +        :ref:`V4L2_FMT_FLAG_ENUM_ALL_FORMATS <v4l2-pix-fmt-flag-set-csc>` has
> +        been set by the userland application.
>
>  Return Value
>  ============
> diff --git a/Documentation/userspace-api/media/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> index bdc628e8c1d6..7a3a1e9dc055 100644
> --- a/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> +++ b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> @@ -216,6 +216,8 @@ replace define V4L2_FMT_FLAG_CSC_YCBCR_ENC fmtdesc-flags
>  replace define V4L2_FMT_FLAG_CSC_HSV_ENC fmtdesc-flags
>  replace define V4L2_FMT_FLAG_CSC_QUANTIZATION fmtdesc-flags
>  replace define V4L2_FMT_FLAG_META_LINE_BASED fmtdesc-flags
> +replace define V4L2_FMT_FLAG_ENUM_ALL_FORMATS fmtdesc-flags
> +replace define V4L2_FMT_FLAG_ALL_FORMATS fmtdesc-flags
>
>  # V4L2 timecode types
>  replace define V4L2_TC_TYPE_24FPS timecode-type
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 4c76d17b4629..5785a98b6ba2 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1569,6 +1569,7 @@ static int v4l_enum_fmt(const struct v4l2_ioctl_ops *ops,
>  	int ret = check_fmt(file, p->type);
>  	u32 mbus_code;
>  	u32 cap_mask;
> +	u32 flags;
>
>  	if (ret)
>  		return ret;
> @@ -1578,8 +1579,10 @@ static int v4l_enum_fmt(const struct v4l2_ioctl_ops *ops,
>  		p->mbus_code = 0;
>
>  	mbus_code = p->mbus_code;
> +	flags = p->flags & V4L2_FMT_FLAG_ENUM_ALL_FORMATS;
>  	memset_after(p, 0, type);
>  	p->mbus_code = mbus_code;
> +	p->flags = flags;
>
>  	switch (p->type) {
>  	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index fe6b67e83751..b6a5da79ba21 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -886,6 +886,8 @@ struct v4l2_fmtdesc {
>  #define V4L2_FMT_FLAG_CSC_HSV_ENC		V4L2_FMT_FLAG_CSC_YCBCR_ENC
>  #define V4L2_FMT_FLAG_CSC_QUANTIZATION		0x0100
>  #define V4L2_FMT_FLAG_META_LINE_BASED		0x0200
> +#define V4L2_FMT_FLAG_ENUM_ALL_FORMATS		0x0400
> +#define V4L2_FMT_FLAG_ALL_FORMATS		0x0800
>
>  	/* Frame Size and frame rate enumeration */
>  /*
> --
> 2.43.0
>
>