linux-kernel - Re: [PATCH 27/55] media: sun6i-isp: Stop abusing of min_buffers

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Date:   Wed, 29 Nov 2023 14:40:27 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc:     hverkuil@...all.nl, mchehab@...nel.org, tfiga@...omium.org,
        m.szyprowski@...sung.com, matt.ranostay@...sulko.com,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-staging@...ts.linux.dev, kernel@...labora.com,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH 27/55] media: sun6i-isp: Stop abusing of
 min_buffers_needed field

Hi Benjamin,

On Mon 27 Nov 23, 17:54, Benjamin Gaignard wrote:
> 'min_buffers_needed' is suppose to be used to indicate the number
> of buffers needed by DMA engine to start streaming.
> sun6i-isp driver doesn't use DMA engine and just want to specify
> the minimum number of buffers to allocate when calling VIDIOC_REQBUFS.
> That 'min_reqbufs_allocation' field purpose so use it.

The hardware actually has its own DMA engine. It can work with just one buffer
though (which will never be returned to userspace). But I think we should still
require at least two buffers allocated, otherwise the driver will be of no use
at all.

So I don't think the commit message here is correct.

Cheers,

Paul

> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> CC: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> CC: Chen-Yu Tsai <wens@...e.org>
> CC: Jernej Skrabec <jernej.skrabec@...il.com>
> CC: Samuel Holland <samuel@...lland.org>
> CC: linux-sunxi@...ts.linux.dev
> ---
>  drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c | 2 +-
>  drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c  | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c b/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c
> index 1595a9607775..f47f9946c19f 100644
> --- a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c
> +++ b/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c
> @@ -660,7 +660,7 @@ int sun6i_isp_capture_setup(struct sun6i_isp_device *isp_dev)
>  	queue->buf_struct_size = sizeof(struct sun6i_isp_buffer);
>  	queue->ops = &sun6i_isp_capture_queue_ops;
>  	queue->mem_ops = &vb2_dma_contig_memops;
> -	queue->min_buffers_needed = 2;
> +	queue->min_reqbufs_allocation = 2;
>  	queue->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>  	queue->lock = &capture->lock;
>  	queue->dev = isp_dev->dev;
> diff --git a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c b/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c
> index e28be895b486..259f6bfcb620 100644
> --- a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c
> +++ b/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c
> @@ -489,7 +489,7 @@ int sun6i_isp_params_setup(struct sun6i_isp_device *isp_dev)
>  	queue->buf_struct_size = sizeof(struct sun6i_isp_buffer);
>  	queue->ops = &sun6i_isp_params_queue_ops;
>  	queue->mem_ops = &vb2_vmalloc_memops;
> -	queue->min_buffers_needed = 1;
> +	queue->min_reqbufs_allocation = 1;
>  	queue->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>  	queue->lock = &params->lock;
>  	queue->dev = isp_dev->dev;
> -- 
> 2.39.2
> 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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