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

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Message-ID: <e7420a20-b17d-493e-9b3c-bbb9314d7025@collabora.com>
Date: Wed, 7 Feb 2024 12:15:02 +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 10:12, Hans Verkuil a écrit :
> Hi Benjamin,
>
> 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.
> So, I came up with the following patch to add back the V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS
> capability. If the DELETE_BUFS ioctl is valid, then it sets this capability
> before calling vidioc_reqbufs or vidioc_create_bufs. So right now it will set
> this for any queue. If we ever want to disable this for a specific queue, then
> either the driver has to override these two ops and clear the flag, or a new
> vb2_queue flag (e.g. disable_delete_bufs) is added and vb2_set_flags_and_caps()
> will clear that capability based on that flag.
>
> In any case, for now just set it for both queues by default.
>
> If you agree that this is a good way to proceed, then can you incorporate this
> into a v20? You can add the documentation for this cap from the v17 version.

Do you want it to be a separate patch or included in the patch introducing DELETE_BUFS ioctl ?

>
> Regards,
>
> 	Hans
>
> Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
> ---
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 8e437104f9c1..64f2d662d068 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -685,7 +685,7 @@ static void vb2_set_flags_and_caps(struct vb2_queue *q, u32 memory,
>   		*flags &= V4L2_MEMORY_FLAG_NON_COHERENT;
>   	}
>
> -	*caps = V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS;
> +	*caps |= V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS;
>   	if (q->io_modes & VB2_MMAP)
>   		*caps |= V4L2_BUF_CAP_SUPPORTS_MMAP;
>   	if (q->io_modes & VB2_USERPTR)
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index a172d33edd19..45bc705e171e 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -2100,6 +2100,7 @@ static int v4l_overlay(const struct v4l2_ioctl_ops *ops,
>   static int v4l_reqbufs(const struct v4l2_ioctl_ops *ops,
>   				struct file *file, void *fh, void *arg)
>   {
> +	struct video_device *vfd = video_devdata(file);
>   	struct v4l2_requestbuffers *p = arg;
>   	int ret = check_fmt(file, p->type);
>
> @@ -2108,6 +2109,9 @@ static int v4l_reqbufs(const struct v4l2_ioctl_ops *ops,
>
>   	memset_after(p, 0, flags);
>
> +	if (is_valid_ioctl(vfd, VIDIOC_DELETE_BUFS))
> +		p->capabilities = V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS;
> +
>   	return ops->vidioc_reqbufs(file, fh, p);
>   }
>
> @@ -2141,6 +2145,7 @@ static int v4l_dqbuf(const struct v4l2_ioctl_ops *ops,
>   static int v4l_create_bufs(const struct v4l2_ioctl_ops *ops,
>   				struct file *file, void *fh, void *arg)
>   {
> +	struct video_device *vfd = video_devdata(file);
>   	struct v4l2_create_buffers *create = arg;
>   	int ret = check_fmt(file, create->format.type);
>
> @@ -2151,6 +2156,9 @@ static int v4l_create_bufs(const struct v4l2_ioctl_ops *ops,
>
>   	v4l_sanitize_format(&create->format);
>
> +	if (is_valid_ioctl(vfd, VIDIOC_DELETE_BUFS))
> +		create->capabilities = V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS;
> +
>   	ret = ops->vidioc_create_bufs(file, fh, create);
>
>   	if (create->format.type == V4L2_BUF_TYPE_VIDEO_CAPTURE ||
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 03443833aaaa..da307f46f903 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1036,6 +1036,7 @@ struct v4l2_requestbuffers {
>   #define V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF	(1 << 5)
>   #define V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS		(1 << 6)
>   #define V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS		(1 << 7)
> +#define V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS		(1 << 8)
>
>   /**
>    * struct v4l2_plane - plane info for multi-planar buffers
>
>
>