linux-kernel - Re: [PATCH v19 0/9] Add DELETE

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Date: Wed, 7 Feb 2024 12:25:08 +0100
From: Benjamin Gaignard <benjamin.gaignard@...labora.com>
To: Hans Verkuil <hverkuil@...all.nl>, mchehab@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 kernel@...labora.com
Subject: Re: [PATCH v19 0/9] Add DELETE_BUF ioctl


Le 07/02/2024 à 11:28, Hans Verkuil a écrit :
> On 06/02/2024 09:58, Hans Verkuil wrote:
>> On 06/02/2024 09:02, Benjamin Gaignard wrote:
>>> Unlike when resolution change on keyframes, dynamic resolution change
>>> on inter frames doesn't allow to do a stream off/on sequence because
>>> it is need to keep all previous references alive to decode inter frames.
>>> This constraint have two main problems:
>>> - more memory consumption.
>>> - more buffers in use.
>>> To solve these issue this series introduce DELETE_BUFS ioctl and remove
>>> the 32 buffers limit per queue.
>> This v19 looks good. There are three outstanding issues that I need to take a
>> look at:
>>
>> 1) Can we still signal support for DELETE_BUFS in the V4L2_BUF_CAP_ caps?
>>     It would be nice to have, but I'm not sure if and how that can be done.
>>
>> 2) I want to take another look at providing a next version of the VIDIOC_CREATE_BUFS
>>     ioctl and how that would possibly influence the design of DELETE_BUFS.
>>     Just to make sure we're not blocking anything or making life harder.
> So I just tried creating a new version of the VIDIOC_CREATE_BUFS ioctl
> that is greatly simplified. This just updates the header, no real code yet:
>
> Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
> ---
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 03443833aaaa..a7398e4c85e7 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -2624,6 +2624,39 @@ struct v4l2_create_buffers {
>   	__u32			reserved[5];
>   };
>
> +/**
> + * struct v4l2_create_buffers_v2 - VIDIOC_CREATE_BUFFERS argument
> + * @type:	enum v4l2_buf_type
> + * @memory:	enum v4l2_memory; buffer memory type
> + * @count:	entry: number of requested buffers,
> + *		return: number of created buffers
> + * @num_planes:	requested number of planes for each buffer
> + * @sizes:	requested plane sizes for each buffer
> + * @start_index:on return, index of the first created buffer
> + * @total_count:on return, the total number of allocated buffers
> + * @capabilities: capabilities of this buffer type.
> + * @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).
> + * @max_num_buffers: if V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS capability flag is set
> + *		this field indicate the maximum possible number of buffers
> + *		for this queue.
> + * @reserved:	future extensions
> + */
> +struct v4l2_create_buffers_v2 {
> +	__u32			type;
> +	__u32			memory;
> +	__u32			count;
> +	__u32			num_planes;
> +	__u32			size[VIDEO_MAX_PLANES];
> +	__u32			start_index;
> +	__u32			total_count;
> +	__u32			capabilities;
> +	__u32			flags;
> +	__u32			max_num_buffers;
> +	__u32			reserved[7];
> +};
> +
>   /**
>    * struct v4l2_delete_buffers - VIDIOC_DELETE_BUFS argument
>    * @index:	the first buffer to be deleted
> @@ -2738,6 +2771,7 @@ struct v4l2_delete_buffers {
>
>   #define VIDIOC_QUERY_EXT_CTRL	_IOWR('V', 103, struct v4l2_query_ext_ctrl)
>   #define VIDIOC_DELETE_BUFS	_IOWR('V', 104, struct v4l2_delete_buffers)
> +#define VIDIOC_CREATE_BUFFERS	_IOWR('V', 105, struct v4l2_create_buffers_v2)
>
>
>   /* Reminder: when adding new ioctls please add support for them to
>
>
> Sadly, struct v4l2_create_buffers was already used for the existing
> VIDIOC_CREATE_BUFS (I wish it was called v4l2_create_bufs...), so I did
> have to add a _v2 suffix. Compared to the old struct it just moves the
> type, num_planes and sizes from v4l2_format into the new struct and drops
> the format field. Note that those fields are the only v4l2_format fields
> that VIDIOC_CREATE_BUFS used, so getting rid of the format makes live
> much easier. I also renamed 'index' to 'start_index' and added a new 'total_count'
> field to report the total number of buffers.
>
> The reason for adding 'total_count' is that VIDIOC_CREATE_BUFS with
> count == 0 would report the total number of buffers in the 'index' field,
> which was rather odd. Adding a specific field for this purpose is nicer.
>
> One thing that might impact your series is the name of the ioctls.
>
> We have:
>
> VIDIOC_CREATE_BUFS/v4l2_create_buffers
> VIDIOC_DELETE_BUFS/v4l2_delete_buffers
> VIDIOC_CREATE_BUFFERS/v4l2_create_buffers_v2 (TBD)
>
> I'm wondering if VIDIOC_DELETE_BUFS should be renamed to
> VIDIOC_DELETE_BUFFERS, that would make it more consistent with
> the proposed VIDIOC_CREATE_BUFFERS.
>
> Alternatively, instead of calling it VIDIOC_CREATE_BUFFERS we
> might call it VIDIOC_CREATE_BUFS_V2.
>
> Or perhaps some other naming convention?

Maybe VIDIOC_NEW_BUFS/v4l2_new_buffers ?

I will wait until naming convention is fixed before send v20.

Regards,
Benjamin

>
> Ideas are welcome.
>
> Regards,
>
> 	Hans
>