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

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Date: Wed, 24 Jan 2024 16:44:45 +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 v17 8/8] media: verisilicon: Support deleting buffers on
 capture queue

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.

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
>>