Re: [PATCH v5 1/7] media: v4l2: Extend pixel formats to unify single/multi-planar handling (and more)

[Helen Koike]

Hi Hans,

On 9/9/20 8:41 AM, Hans Verkuil wrote:
> 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@xxxxxxxxxxxxx>
>> Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
>> ---
>> 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).

We discussed this on v4 https://patchwork.linuxtv.org/project/linux-media/cover/20200717115435.2632623-1-helen.koike@xxxxxxxxxxxxx/

The idea is to replace V4L2_PIX_FMT_FLAG_PREMUL_ALPHA by a modifier, and this API
won't need CSC, since the colorspace fields are read-write.

Regards,
Helen

> 
>> +	__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
>