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

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Message-ID: <c2bbab59-1b07-4a3c-985c-be01836af756@xs4all.nl>
Date: Wed, 7 Feb 2024 12:20:22 +0100
From: Hans Verkuil <hverkuil@...all.nl>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>, 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

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.

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
>>
>>
>>