Re: [PATCH v4 2/6] media: v4l2: Add extended buffer operations

[Helen Koike]

Hi,

On 7/21/20 8:26 AM, Stanimir Varbanov wrote:
> 
> 
> On 7/17/20 2:54 PM, Helen Koike wrote:
>> From: Hans Verkuil <hans.verkuil@xxxxxxxxx>
>>
>> Those extended buffer ops have several purpose:
>> 1/ Fix y2038 issues by converting the timestamp into an u64 counting
>>    the number of ns elapsed since 1970
>> 2/ Unify single/multiplanar handling
>> 3/ Add a new start offset field to each v4l2 plane buffer info struct
>>    to support the case where a single buffer object is storing all
>>    planes data, each one being placed at a different offset
>>
>> New hooks are created in v4l2_ioctl_ops so that drivers can start using
>> these new objects.
>>
>> The core takes care of converting new ioctls requests to old ones
>> if the driver does not support the new hooks, and vice versa.
>>
>> Note that the timecode field is gone, since there doesn't seem to be
>> in-kernel users. We can be added back in the reserved area if needed or
>> use the Request API to collect more metadata information from the
>> frame.
>>
>> Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
>> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
>> Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
>> ---
>> 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.
>> - Drop VIDIOC_EXT_EXPBUF, since the only difference from VIDIOC_EXPBUF
>> was that with VIDIOC_EXT_EXPBUF we could export multiple planes at once.
>> I think we can add this later, so I removed it from this RFC to simplify it.
>> - Remove num_planes field from struct v4l2_ext_buffer
>> - Add flags field to struct v4l2_ext_create_buffers
>> - Reformulate struct v4l2_ext_plane
>> - Fix some bugs caught by v4l2-compliance
>> - 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:
>> - Add reserved space to v4l2_ext_buffer so that new fields can be added
>>   later on
>> ---
>>  drivers/media/v4l2-core/v4l2-dev.c   |  29 ++-
>>  drivers/media/v4l2-core/v4l2-ioctl.c | 349 +++++++++++++++++++++++++--
>>  include/media/v4l2-ioctl.h           |  26 ++
>>  include/uapi/linux/videodev2.h       |  89 +++++++
>>  4 files changed, 471 insertions(+), 22 deletions(-)
>>
> 
> <cut>
> 
>> +/**
>> + * struct v4l2_ext_plane - extended plane buffer info
>> + * @buffer_length:	size of the entire buffer in bytes, should fit
>> + *			@offset + @plane_length
>> + * @plane_length:	size of the plane in bytes.
>> + * @userptr:		when memory is V4L2_MEMORY_USERPTR, a userspace pointer pointing
>> + *			to this plane.
>> + * @dmabuf_fd:		when memory is V4L2_MEMORY_DMABUF, a userspace file descriptor
>> + *			associated with this plane.
>> + * @offset:		offset in the memory buffer where the plane starts. If
>> + *			V4L2_MEMORY_MMAP is used, then it can be a "cookie" that
>> + *			should be passed to mmap() called on the video node.
>> + * @reserved:		extra space reserved for future fields, must be set to 0.
>> + *
>> + *
>> + * Buffers consist of one or more planes, e.g. an YCbCr buffer with two planes
>> + * can have one plane for Y, and another for interleaved CbCr components.
>> + * Each plane can reside in a separate memory buffer, or even in
>> + * a completely separate memory node (e.g. in embedded devices).
>> + */
>> +struct v4l2_ext_plane {
>> +	__u32 buffer_length;
>> +	__u32 plane_length;
>> +	union {
>> +		__u64 userptr;
>> +		__s32 dmabuf_fd;
>> +	} m;
>> +	__u32 offset;
>> +	__u32 reserved[4];
>> +};
>> +
>>  /**
>>   * struct v4l2_buffer - video buffer info
>>   * @index:	id number of the buffer
>> @@ -1055,6 +1086,36 @@ struct v4l2_buffer {
>>  	};
>>  };
>>  
>> +/**
>> + * struct v4l2_ext_buffer - extended video buffer info
>> + * @index:	id number of the buffer
>> + * @type:	V4L2_BUF_TYPE_VIDEO_CAPTURE or V4L2_BUF_TYPE_VIDEO_OUTPUT
>> + * @flags:	buffer informational flags
>> + * @field:	enum v4l2_field; field order of the image in the buffer
>> + * @timestamp:	frame timestamp
>> + * @sequence:	sequence count of this frame
>> + * @memory:	enum v4l2_memory; the method, in which the actual video data is
>> + *		passed
>> + * @planes:	per-plane buffer information
>> + * @request_fd:	fd of the request that this buffer should use
>> + * @reserved:	extra space reserved for future fields, must be set to 0
>> + *
>> + * Contains data exchanged by application and driver using one of the Streaming
>> + * I/O methods.
>> + */
>> +struct v4l2_ext_buffer {
>> +	__u32 index;
>> +	__u32 type;
>> +	__u32 flags;
>> +	__u32 field;
>> +	__u64 timestamp;
>> +	__u32 sequence;
>> +	__u32 memory;
>> +	__u32 request_fd;
> 
> This should be __s32, at least for consistency with dmabuf_fd?

I see that in struct v4l2_buffer, we have __s32, I don't mind changing it
to keep the consistency, I just don't see where this value can be a negative
number.

> 
>> +	struct v4l2_ext_plane planes[VIDEO_MAX_PLANES];
>> +	__u32 reserved[4];
> 
> I think we have to reserve more words here for future extensions.
> 
> I'd like also to propose to add here __s32 metadata_fd. The idea behind
> this is to have a way to pass per-frame metadata dmabuf buffers for
> synchronous type of metadata where the metadata is coming at the same
> time with data buffers. What would be the format of the metadata buffer
> is TBD.
> 
> One option for metadata buffer format could be:
> 
> header {
> 	num_ctrls
> 	array_of_ctrls [0..N]
> 		ctrl_id
> 		ctrl_size
> 		ctrl_offset
> }
> 
> data {
> 	cid0	//offset of cid0 in dmabuf buffer
> 	cid1
> 	cidN
> }

Would it be better if, instead of adding a medatata_fd inside struct v4l2_ext_buffer,
we create a new ioctl that gets this structs for the controls and sync them using the
Request API ?

I'd like to avoid too much metadata in the buffer object.

Regards,
Helen

> 
> This will make easy to get concrete ctrl id without a need to parse the
> whole metadata buffer. Also using dmabuf we don't need to copy data
> between userspace <-> kernelspace (just cache syncs through
> begin/end_cpu_access).
> 
> The open question is who will validate the metadata buffer when it comes
> from userspace. The obvious answer is v4l2-core but looking into DRM
> subsytem they give more freedom to the drivers, and just provide generic
> helpers which are not mandatory.
> 
> I guess this will be a voice in the wilderness but I wanted to know your
> opinion.
> 
>> +};
>> +
>>  #ifndef __KERNEL__
>>  /**
>>   * v4l2_timeval_to_ns - Convert timeval to nanoseconds
>> @@ -2520,6 +2581,29 @@ struct v4l2_create_buffers {
>>  	__u32			reserved[6];
>>  };
>>  
>> +/**
>> + * struct v4l2_ext_create_buffers - VIDIOC_EXT_CREATE_BUFS argument
>> + * @index:	on return, index of the first created buffer
>> + * @count:	entry: number of requested buffers,
>> + *		return: number of created buffers
>> + * @memory:	enum v4l2_memory; buffer memory type
>> + * @capabilities: capabilities of this buffer type.
>> + * @format:	frame format, for which buffers are requested
>> + * @flags:	additional buffer management attributes (ignored unless the
>> + *		queue has V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS capability
>> + *		and configured for MMAP streaming I/O).
>> + * @reserved:	extra space reserved for future fields, must be set to 0
>> + */
>> +struct v4l2_ext_create_buffers {
>> +	__u32				index;
>> +	__u32				count;
>> +	__u32				memory;
>> +	struct v4l2_ext_pix_format	format;
>> +	__u32				capabilities;
>> +	__u32				flags;
>> +	__u32 reserved[4];
>> +};
>> +
>>  /*
>>   *	I O C T L   C O D E S   F O R   V I D E O   D E V I C E S
>>   *
>> @@ -2623,6 +2707,11 @@ struct v4l2_create_buffers {
>>  #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)
>> +#define VIDIOC_EXT_CREATE_BUFS	_IOWR('V', 107, struct v4l2_ext_create_buffers)
>> +#define VIDIOC_EXT_QUERYBUF	_IOWR('V', 108, struct v4l2_ext_buffer)
>> +#define VIDIOC_EXT_QBUF		_IOWR('V', 109, struct v4l2_ext_buffer)
>> +#define VIDIOC_EXT_DQBUF	_IOWR('V', 110, struct v4l2_ext_buffer)
>> +#define VIDIOC_EXT_PREPARE_BUF	_IOWR('V', 111, struct v4l2_ext_buffer)
>>  
>>  /* Reminder: when adding new ioctls please add support for them to
>>     drivers/media/v4l2-core/v4l2-compat-ioctl32.c as well! */
>>
>