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

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Date: Wed, 24 Jan 2024 16:35:08 +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 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.

>
>>   
>>   	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
>