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Date:   Wed, 9 Sep 2020 13:41:31 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Helen Koike <helen.koike@...labora.com>, mchehab@...nel.org,
        laurent.pinchart@...asonboard.com, sakari.ailus@....fi,
        linux-media@...r.kernel.org
Cc:     Boris Brezillon <boris.brezillon@...labora.com>,
        tfiga@...omium.org, hiroh@...omium.org, nicolas@...fresne.ca,
        Brian.Starkey@....com, kernel@...labora.com,
        narmstrong@...libre.com, linux-kernel@...r.kernel.org,
        frkoenig@...omium.org, mjourdan@...libre.com,
        stanimir.varbanov@...aro.org
Subject: Re: [PATCH v5 1/7] media: v4l2: Extend pixel formats to unify
 single/multi-planar handling (and more)

Hi Helen,

Some review comments, concentrating on the uAPI.

On 04/08/2020 21:29, Helen Koike wrote:
> This is part of the multiplanar and singleplanar unification process.
> v4l2_ext_pix_format is supposed to work for both cases.
> 
> We also add the concept of modifiers already employed in DRM to expose
> HW-specific formats (like tiled or compressed formats) and allow
> exchanging this information with the DRM subsystem in a consistent way.
> 
> Note that only V4L2_BUF_TYPE_VIDEO_[OUTPUT,CAPTURE] are accepted in
> v4l2_ext_format, other types will be rejected if you use the
> {G,S,TRY}_EXT_PIX_FMT ioctls.
> 
> New hooks have been added to v4l2_ioctl_ops to support those new ioctls
> in drivers, but, in the meantime, the core takes care of converting
> {S,G,TRY}_EXT_PIX_FMT requests into {S,G,TRY}_FMT so that old drivers can
> still work if the userspace app/lib uses the new ioctls.
> The conversion is also done the other around to allow userspace
> apps/libs using {S,G,TRY}_FMT to work with drivers implementing the
> _ext_ hooks.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@...labora.com>
> Signed-off-by: Helen Koike <helen.koike@...labora.com>
> ---
> Changes in v5:
> - change sizes and reorder fields to avoid holes in the struct and make
>   it the same for 32 and 64 bits
> - removed __attribute__ ((packed)) from uapi structs
> - Fix doc warning from make htmldocs
> - Updated commit message with EXT_PIX prefix for the ioctls.
> 
> Changes in v4:
> - Use v4l2_ext_pix_format directly in the ioctl, drop v4l2_ext_format,
> making V4L2_BUF_TYPE_VIDEO_[OUTPUT,CAPTURE] the only valid types.
> - Add reserved fields
> - Removed num_planes from struct v4l2_ext_pix_format
> - Removed flag field from struct v4l2_ext_pix_format, since the only
>   defined value is V4L2_PIX_FMT_FLAG_PREMUL_ALPHA only used by vsp1,
>   where we can use modifiers, or add it back later through the reserved
>   bits.
> - In v4l2_ext_format_to_format(), check if modifier is != MOD_LINEAR &&
>   != MOD_INVALID
> - Fix type assignment in v4l_g_fmt_ext_pix()
> - Rebased on top of media/master (post 5.8-rc1)
> 
> Changes in v3:
> - Rebased on top of media/master (post 5.4-rc1)
> 
> Changes in v2:
> - Move the modifier in v4l2_ext_format (was formerly placed in
>   v4l2_ext_plane)
> - Fix a few bugs in the converters and add a strict parameter to
>   allow conversion of uninitialized/mis-initialized objects
> ---
>  drivers/media/v4l2-core/v4l2-dev.c   |  21 +-
>  drivers/media/v4l2-core/v4l2-ioctl.c | 585 +++++++++++++++++++++++----
>  include/media/v4l2-ioctl.h           |  34 ++
>  include/uapi/linux/videodev2.h       |  56 +++
>  4 files changed, 615 insertions(+), 81 deletions(-)
> 

<snip>

> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index c7b70ff53bc1d..7123c6a4d9569 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -2254,6 +2254,58 @@ struct v4l2_pix_format_mplane {
>  	__u8				reserved[7];
>  } __attribute__ ((packed));
>  
> +/**
> + * struct v4l2_plane_ext_pix_format - additional, per-plane format definition
> + * @sizeimage:		maximum size in bytes required for data, for which
> + *			this plane will be used.
> + *			Should be set to zero for unused planes.
> + * @bytesperline:	distance in bytes between the leftmost pixels in two
> + *			adjacent lines
> + * @reserved:		extra space reserved for future fields, must be set to 0
> + */
> +struct v4l2_plane_ext_pix_format {
> +	__u32 sizeimage;
> +	__u32 bytesperline;
> +	__u32 reserved;

I'd use reserved[4] here.

> +};
> +
> +/**
> + * struct v4l2_ext_pix_format - extended single/multiplanar format definition
> + * @type:		type of the data stream; V4L2_BUF_TYPE_VIDEO_CAPTURE or
> + *			V4L2_BUF_TYPE_VIDEO_OUTPUT
> + * @width:		image width in pixels
> + * @height:		image height in pixels
> + * @field:		enum v4l2_field; field order (for interlaced video)
> + * @pixelformat:	little endian four character code (fourcc)
> + * @modifier:		modifier applied to the format (used for tiled formats
> + *			and other kind of HW-specific formats, like compressed
> + *			formats)

This should refer to the drm.h header since we're reusing the DRM modifiers.

> + * @colorspace:		enum v4l2_colorspace; supplemental to pixelformat
> + * @plane_fmt:		per-plane information
> + * @ycbcr_enc:		enum v4l2_ycbcr_encoding, Y'CbCr encoding
> + * @hsv_enc:		enum v4l2_hsv_encoding, HSV encoding
> + * @quantization:	enum v4l2_quantization, colorspace quantization
> + * @xfer_func:		enum v4l2_xfer_func, colorspace transfer function
> + * @reserved:		extra space reserved for future fields, must be set to 0
> + */
> +struct v4l2_ext_pix_format {
> +	__u32 type;
> +	__u32 width;
> +	__u32 height;
> +	__u32 field;
> +	__u64 modifier;
> +	__u32 pixelformat;
> +	__u32 colorspace;
> +	struct v4l2_plane_ext_pix_format plane_fmt[VIDEO_MAX_PLANES];
> +	union {
> +		__u32 ycbcr_enc;
> +		__u32 hsv_enc;
> +	};
> +	__u32 quantization;
> +	__u32 xfer_func;

I'd reorder this:

	struct v4l2_plane_ext_pix_format plane_fmt[VIDEO_MAX_PLANES];
	__u32 pixelformat;
	__u32 colorspace;
	__u32 xfer_func;
	union {
		__u32 ycbcr_enc;
		__u32 hsv_enc;
	};
	__u32 quantization;

The reason for reordering is that I like to keep the colorimetry fields in
that order since that is how these fields are processed mathematically: you
apply the colorspace matrix first, then the transfer function, then optionally
convert to Y'CbCr or HSV and finally you quantize the result.

There is also a __u32 flags; field missing (needed for V4L2_PIX_FMT_FLAG_PREMUL_ALPHA
and for the upcoming CSC support).

> +	__u32 reserved[9];
> +};
> +
>  /**
>   * struct v4l2_sdr_format - SDR format definition
>   * @pixelformat:	little endian four character code (fourcc)
> @@ -2571,6 +2623,10 @@ struct v4l2_create_buffers {
>  
>  #define VIDIOC_QUERY_EXT_CTRL	_IOWR('V', 103, struct v4l2_query_ext_ctrl)
>  
> +#define VIDIOC_G_EXT_PIX_FMT	_IOWR('V', 104, struct v4l2_ext_pix_format)
> +#define VIDIOC_S_EXT_PIX_FMT	_IOWR('V', 105, struct v4l2_ext_pix_format)
> +#define VIDIOC_TRY_EXT_PIX_FMT	_IOWR('V', 106, struct v4l2_ext_pix_format)
> +
>  /* Reminder: when adding new ioctls please add support for them to
>     drivers/media/v4l2-core/v4l2-compat-ioctl32.c as well! */
>  
> 

Regards,

	Hans

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