linux-kernel - Re: [PATCH v3] media: nxp: imx8-isi: better handle the m2m usage

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Message-ID: <20250206203749.GD7524@pendragon.ideasonboard.com>
Date: Thu, 6 Feb 2025 22:37:49 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Laurentiu Palcu <laurentiu.palcu@....nxp.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Dong Aisheng <aisheng.dong@....com>,
	Jacopo Mondi <jacopo@...ndi.org>, Christian Hemp <c.hemp@...tec.de>,
	Guoniu Zhou <guoniu.zhou@....com>,
	Stefan Riedmueller <s.riedmueller@...tec.de>,
	linux-media@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] media: nxp: imx8-isi: better handle the m2m
 usage_count

Hi Laurentiu,

Thank you for the patch.

On Wed, Oct 23, 2024 at 11:56:43AM +0300, Laurentiu Palcu wrote:
> Currently, if streamon/streamoff calls are imbalanced we can either end up
> with a negative ISI m2m usage_count (if streamoff() is called more times
> than streamon()) in which case we'll not be able to restart the ISI pipe
> next time, or the usage_count never gets to 0 and the pipe is never
> switched off.
> 
> To avoid that, add a 'streaming' flag to mxc_isi_m2m_ctx_queue_data and use it
> in the streamon/streamoff to avoid incrementing/decrementing the usage_count
> uselessly, if called multiple times from the same context.
> 
> Fixes: cf21f328fcafac ("media: nxp: Add i.MX8 ISI driver")
> Suggested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Signed-off-by: Laurentiu Palcu <laurentiu.palcu@....nxp.com>
> ---
> v3:
>  * Changed the implementation as suggested by Laurent and add a Suggested-by
>    tag to reflect that;
> 
> v2:
>  * Changed the way 'usage_count' is incremented/decremented by taking
>    into account the context the streamon/streamoff functions are called
>    from;
>  * Changed the commit message and subject to reflect the changes;
> 
>  drivers/media/platform/nxp/imx8-isi/imx8-isi-m2m.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-m2m.c b/drivers/media/platform/nxp/imx8-isi/imx8-isi-m2m.c
> index 9745d6219a166..dc10e1a9f27c1 100644
> --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-m2m.c
> +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-m2m.c
> @@ -43,6 +43,7 @@ struct mxc_isi_m2m_ctx_queue_data {
>  	struct v4l2_pix_format_mplane format;
>  	const struct mxc_isi_format_info *info;
>  	u32 sequence;
> +	bool streaming;
>  };
>  
>  struct mxc_isi_m2m_ctx {
> @@ -486,6 +487,7 @@ static int mxc_isi_m2m_streamon(struct file *file, void *fh,
>  				enum v4l2_buf_type type)
>  {
>  	struct mxc_isi_m2m_ctx *ctx = to_isi_m2m_ctx(fh);
> +	struct mxc_isi_m2m_ctx_queue_data *q = mxc_isi_m2m_ctx_qdata(ctx, type);
>  	const struct v4l2_pix_format_mplane *out_pix = &ctx->queues.out.format;
>  	const struct v4l2_pix_format_mplane *cap_pix = &ctx->queues.cap.format;
>  	const struct mxc_isi_format_info *cap_info = ctx->queues.cap.info;
> @@ -495,6 +497,9 @@ static int mxc_isi_m2m_streamon(struct file *file, void *fh,
>  

While at it I'll drop the blank line here when applying the patch.

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

>  	int ret;
>  
> +	if (q->streaming)
> +		return 0;
> +
>  	mutex_lock(&m2m->lock);
>  
>  	if (m2m->usage_count == INT_MAX) {
> @@ -547,6 +552,8 @@ static int mxc_isi_m2m_streamon(struct file *file, void *fh,
>  		goto unchain;
>  	}
>  
> +	q->streaming = true;
> +
>  	return 0;
>  
>  unchain:
> @@ -569,10 +576,14 @@ static int mxc_isi_m2m_streamoff(struct file *file, void *fh,
>  				 enum v4l2_buf_type type)
>  {
>  	struct mxc_isi_m2m_ctx *ctx = to_isi_m2m_ctx(fh);
> +	struct mxc_isi_m2m_ctx_queue_data *q = mxc_isi_m2m_ctx_qdata(ctx, type);
>  	struct mxc_isi_m2m *m2m = ctx->m2m;
>  
>  	v4l2_m2m_ioctl_streamoff(file, fh, type);
>  
> +	if (!q->streaming)
> +		return 0;
> +
>  	mutex_lock(&m2m->lock);
>  
>  	/*
> @@ -598,6 +609,8 @@ static int mxc_isi_m2m_streamoff(struct file *file, void *fh,
>  
>  	mutex_unlock(&m2m->lock);
>  
> +	q->streaming = false;
> +
>  	return 0;
>  }
>  

-- 
Regards,

Laurent Pinchart