linux-kernel - Re: [PATCH v17 8/8] media: verisilicon: Support deleting buffers on capture queue

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Date: Thu, 25 Jan 2024 10:27:51 +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 v17 8/8] media: verisilicon: Support deleting buffers on
 capture queue


Le 24/01/2024 à 16:44, Hans Verkuil a écrit :
> On 24/01/2024 16:35, Benjamin Gaignard wrote:
>> Le 24/01/2024 à 13:52, Hans Verkuil a écrit :
>>> On 19/01/2024 10:49, Benjamin Gaignard wrote:
>>>> Allow to delete buffers on capture queue because it the one which
>>>> own the decoded buffers. After a dynamic resolution change lot of
>>>> them could remain allocated but won't be used anymore so deleting
>>>> them save memory.
>>>> Do not add this feature on output queue because the buffers are
>>>> smaller, fewer and always recycled even after a dynamic resolution
>>>> change.
>>>>
>>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>>>> ---
>>>>    drivers/media/platform/verisilicon/hantro_drv.c  | 1 +
>>>>    drivers/media/platform/verisilicon/hantro_v4l2.c | 1 +
>>>>    2 files changed, 2 insertions(+)
>>>>
>>>> diff --git a/drivers/media/platform/verisilicon/hantro_drv.c b/drivers/media/platform/verisilicon/hantro_drv.c
>>>> index db3df6cc4513..f6b0a676a740 100644
>>>> --- a/drivers/media/platform/verisilicon/hantro_drv.c
>>>> +++ b/drivers/media/platform/verisilicon/hantro_drv.c
>>>> @@ -248,6 +248,7 @@ queue_init(void *priv, struct vb2_queue *src_vq, struct vb2_queue *dst_vq)
>>>>        dst_vq->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_COPY;
>>>>        dst_vq->lock = &ctx->dev->vpu_mutex;
>>>>        dst_vq->dev = ctx->dev->v4l2_dev.dev;
>>>> +    src_vq->supports_delete_bufs = true;
>>> As I mentioned, I remain unconvinced by this. It is just making the API inconsistent
>>> since if you support delete_bufs, then why support it for one queue only and not both?
>> Because the both queues don't handle the same type of data.
>> For example for a stateless decoder, for me, it makes sense to allow delete decoded frames
>> if they won't be used anymore but that won't makes sense for bitstream buffers.
> But is there any reason why you wouldn't support this feature? We support VIDIOC_CREATE_BUFS
> as well, even though most drivers do not need it, but it is cheap to add.
>
> Deleting buffers is a generic feature, and I don't see why you wouldn't just offer it
> for both queues.

You want me to remove supports_delete_bufs and V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS ?
This way we can remove buffers from the both queues.
Sound good for you ?

Regards,
Benjamin

>
> Regards,
>
> 	Hans
>
>>>>          return vb2_queue_init(dst_vq);
>>>>    }
>>>> diff --git a/drivers/media/platform/verisilicon/hantro_v4l2.c b/drivers/media/platform/verisilicon/hantro_v4l2.c
>>>> index 941fa23c211a..34eab90e8a42 100644
>>>> --- a/drivers/media/platform/verisilicon/hantro_v4l2.c
>>>> +++ b/drivers/media/platform/verisilicon/hantro_v4l2.c
>>>> @@ -756,6 +756,7 @@ const struct v4l2_ioctl_ops hantro_ioctl_ops = {
>>>>        .vidioc_dqbuf = v4l2_m2m_ioctl_dqbuf,
>>>>        .vidioc_prepare_buf = v4l2_m2m_ioctl_prepare_buf,
>>>>        .vidioc_create_bufs = v4l2_m2m_ioctl_create_bufs,
>>>> +    .vidioc_delete_bufs = v4l2_m2m_ioctl_delete_bufs,
>>>>        .vidioc_expbuf = v4l2_m2m_ioctl_expbuf,
>>>>          .vidioc_subscribe_event = v4l2_ctrl_subscribe_event,
>>> In my view setting vidioc_delete_bufs should enable this feature, and if
>>> for some strange reason only one queue support it, then make a wrapper
>>> callback that returns an error when used with the wrong queue.
>>>
>>> Also note that patch 6/8 never checks for q->supports_delete_bufs in
>>> vb2_core_delete_bufs(), which is wrong!
>> I will fix that in next version.
>> Regards,
>> Benjamin
>>
>>> Regards,
>>>
>>>      Hans
>>>
>