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

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Date: Wed, 24 Jan 2024 13:52:13 +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 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?

>  
>  	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!

Regards,

	Hans