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Date:   Wed, 29 Nov 2023 14:40:27 +0100
From:   Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To:     Benjamin Gaignard <benjamin.gaignard@collabora.com>
Cc:     hverkuil@xs4all.nl, mchehab@kernel.org, tfiga@chromium.org,
        m.szyprowski@samsung.com, matt.ranostay@konsulko.com,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        linux-staging@lists.linux.dev, kernel@collabora.com,
        Chen-Yu Tsai <wens@csie.org>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Samuel Holland <samuel@sholland.org>,
        linux-sunxi@lists.linux.dev
Subject: Re: [PATCH 27/55] media: sun6i-isp: Stop abusing of
 min_buffers_needed field
Message-ID: <ZWc_S8CuPyc9zRXz@aptenodytes>
References: <20231127165454.166373-1-benjamin.gaignard@collabora.com>
 <20231127165454.166373-28-benjamin.gaignard@collabora.com>
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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 buf=
fer
though (which will never be returned to userspace). But I think we should s=
till
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@collabora.com>
> CC: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> CC: Chen-Yu Tsai <wens@csie.org>
> CC: Jernej Skrabec <jernej.skrabec@gmail.com>
> CC: Samuel Holland <samuel@sholland.org>
> CC: linux-sunxi@lists.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(-)
>=20
> 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 =3D sizeof(struct sun6i_isp_buffer);
>  	queue->ops =3D &sun6i_isp_capture_queue_ops;
>  	queue->mem_ops =3D &vb2_dma_contig_memops;
> -	queue->min_buffers_needed =3D 2;
> +	queue->min_reqbufs_allocation =3D 2;
>  	queue->timestamp_flags =3D V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>  	queue->lock =3D &capture->lock;
>  	queue->dev =3D isp_dev->dev;
> diff --git a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c b/d=
rivers/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 *i=
sp_dev)
>  	queue->buf_struct_size =3D sizeof(struct sun6i_isp_buffer);
>  	queue->ops =3D &sun6i_isp_params_queue_ops;
>  	queue->mem_ops =3D &vb2_vmalloc_memops;
> -	queue->min_buffers_needed =3D 1;
> +	queue->min_reqbufs_allocation =3D 1;
>  	queue->timestamp_flags =3D V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>  	queue->lock =3D &params->lock;
>  	queue->dev =3D isp_dev->dev;
> --=20
> 2.39.2
>=20

--=20
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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