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

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Date: Wed, 7 Feb 2024 12:22:46 +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 12:20, Hans Verkuil a écrit :
> On 07/02/2024 12:15, Benjamin Gaignard wrote:
>> 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 ?
> Up to you, whatever makes the most sense.

I will include it in DELETE_BUFS patch because it is strongly related to it.

Regards,
Benjamin

>
> Regards,
>
> 	Hans
>
>>> 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
>>>
>>>
>>>