linux-kernel - Re: [PATCH v12 22/56] media: pci: tw686x: Set min_buffers

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Date:   Wed, 18 Oct 2023 12:19:16 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        mchehab@...nel.org, tfiga@...omium.org, m.szyprowski@...sung.com,
        ming.qian@....com, ezequiel@...guardiasur.com.ar,
        p.zabel@...gutronix.de, gregkh@...uxfoundation.org,
        nicolas.dufresne@...labora.com
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
        kernel@...labora.com
Subject: Re: [PATCH v12 22/56] media: pci: tw686x: Set min_buffers_needed to 3

On 17/10/2023 16:47, Benjamin Gaignard wrote:
> vb2 queue_setup checks for a minimum number of buffers so set
> min_buffers_needed to 3 and remove the useless check in
> tw686x_queue_setup().
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> CC: Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
> ---
>  drivers/media/pci/tw686x/tw686x-video.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/pci/tw686x/tw686x-video.c b/drivers/media/pci/tw686x/tw686x-video.c
> index 3ebf7a2c95f0..74cd864365aa 100644
> --- a/drivers/media/pci/tw686x/tw686x-video.c
> +++ b/drivers/media/pci/tw686x/tw686x-video.c
> @@ -426,13 +426,6 @@ static int tw686x_queue_setup(struct vb2_queue *vq,
>  	unsigned int szimage =
>  		(vc->width * vc->height * vc->format->depth) >> 3;
>  
> -	/*
> -	 * Let's request at least three buffers: two for the
> -	 * DMA engine and one for userspace.
> -	 */
> -	if (vq->num_buffers + *nbuffers < 3)
> -		*nbuffers = 3 - vq->num_buffers;
> -
>  	if (*nplanes) {
>  		if (*nplanes != 1 || sizes[0] < szimage)
>  			return -EINVAL;
> @@ -1221,7 +1214,11 @@ int tw686x_video_init(struct tw686x_dev *dev)
>  		vc->vidq.ops = &tw686x_video_qops;
>  		vc->vidq.mem_ops = dev->dma_ops->mem_ops;
>  		vc->vidq.timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
> -		vc->vidq.min_buffers_needed = 2;
> +		/*
> +		 * Let's request at least three buffers: two for the
> +		 * DMA engine and one for userspace.
> +		 */
> +		vc->vidq.min_buffers_needed = 3;

Don't touch min_buffers_needed, just keep the current check in queue_setup.

Regards,

	Hans

>  		vc->vidq.lock = &vc->vb_mutex;
>  		vc->vidq.gfp_flags = dev->dma_mode != TW686X_DMA_MODE_MEMCPY ?
>  				     GFP_DMA32 : 0;