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Date: Thu, 25 Jan 2024 10:50:44 +0100
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Subject: Re: [PATCH v17 8/8] media: verisilicon: Support deleting buffers on
 capture queue
To: Benjamin Gaignard <benjamin.gaignard@collabora.com>, mchehab@kernel.org
Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
 kernel@collabora.com
References: <20240119094944.26763-1-benjamin.gaignard@collabora.com>
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From: Hans Verkuil <hverkuil@xs4all.nl>
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In-Reply-To: <41e69449-c797-44d1-b832-d4972915bb6d@collabora.com>
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On 25/01/2024 10:27, Benjamin Gaignard wrote:
> 
> 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@collabora.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 ?

The capability is still nice to have, but it is a bit tricky to set it since you
need to check if the vidioc_delete_bufs callback is set.

For now drop this cap, I'll have to think about it.

Regards,

	Hans

> 
> 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
>>>>
>>