[PATCH v4 1/2] media: videodev2: Add flags to unconditionnaly enumerate pixels formats

Fri Jul 19 06:15:56 PDT 2024

On 17/07/2024 15:14, 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 at collabora.com>
> ---
> changes in version 4:
> - Explicitly document that the new flags are targeting mem2mem devices.
> 
>  .../userspace-api/media/v4l/dev-stateless-decoder.rst |  6 ++++++
>  .../userspace-api/media/v4l/vidioc-enum-fmt.rst       | 11 +++++++++++
>  .../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, 24 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..15bc2f59c05a 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
> @@ -234,6 +234,17 @@ 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 flag is relevant only for mem2mem devices.
> +    * - ``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.
> +        This flag is relevant only for mem2mem devices.
>  
>  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

For reasons mentioned earlier, you cannot make the flags field an input to the
driver, that will almost certainly break some applications that do not zero
the flags field today, since they expect it to be set by the driver.

What probably will work is to add a flag to the index field: this would be
similar to what I do in VIDIOC_QUERYCTRL where you can OR the id field with
V4L2_CTRL_FLAG_NEXT_CTRL to modify the behavior.

It is perfectly fine to use the top bits of the index for this.

Drivers that do not support this will just fail with EINVAL, and drivers that
do support this will return a proper format.

Applications can easily test support for this by just calling ENUM_FMT with 0
ORed with the new flag: if it is supported, then it will return 0, otherwise
-EINVAL.

With this scheme I think you can also drop the proposed V4L2_FMT_FLAG_ALL_FORMATS
flag.

But as I mentioned in my reply to the cover letter of this series, I am not
convinced we really need this, and if we do, then I am not convinced about
the name of the flag.

And I would also like to know if such a feature can be used by m2m drivers
that are not codecs (e.g. scalers, csc converters), and if that would impact
the name/description of the flag.

It is currently very specific for decoders, but I prefer to see a more general
solution, not just for one specific corner case.

Regards,

	Hans

>  
>  	/* Frame Size and frame rate enumeration */
>  /*