linux-kernel - Re: [PATCH v2 2/2] media: iris: Fix fps calculation

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Message-ID: <a90943c6-0e7f-51cb-05d6-41e131797196@oss.qualcomm.com>
Date: Tue, 23 Dec 2025 15:09:29 +0530
From: Dikshita Agarwal <dikshita.agarwal@....qualcomm.com>
To: Ricardo Ribalda <ribalda@...omium.org>, Keke Li <keke.li@...ogic.com>,
        Jacopo Mondi <jacopo.mondi@...asonboard.com>,
        Daniel Scally <dan.scally@...asonboard.com>,
        Hans Verkuil <hverkuil+cisco@...nel.org>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Vikash Garodia <vikash.garodia@....qualcomm.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Bryan O'Donoghue <bod@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 2/2] media: iris: Fix fps calculation



On 12/16/2025 9:12 PM, Ricardo Ribalda wrote:
> iris_venc_s_param() uses do_div to divide two 64 bits operators, this is
> wrong. Luckily for us, both of the operators fit in 32 bits, so we can use
> a normal division.
> 
> Now that we are at it, mark the fps smaller than 1 as invalid, the code
> does not seem to handle them properly.
> 
> The following cocci warning is fixed with this patch:
> ./platform/qcom/iris/iris_venc.c:378:1-7: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead
> 
> Fixes: 4ff586ff28e3 ("media: iris: Add support for G/S_PARM for encoder video device")
> Reviewed-by: Dikshita Agarwal <dikshita.agarwal@....qualcomm.com>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/platform/qcom/iris/iris_venc.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/media/platform/qcom/iris/iris_venc.c b/drivers/media/platform/qcom/iris/iris_venc.c
> index 5830eba93c68b27fa9db87bac63a691eaca338d2..3b941aeb55a2f498898a27a5f8cb58cdb26fdfed 100644
> --- a/drivers/media/platform/qcom/iris/iris_venc.c
> +++ b/drivers/media/platform/qcom/iris/iris_venc.c
> @@ -382,8 +382,7 @@ int iris_venc_s_param(struct iris_inst *inst, struct v4l2_streamparm *s_parm)
>  	struct v4l2_fract *timeperframe = NULL;
>  	u32 default_rate = DEFAULT_FPS;
>  	bool is_frame_rate = false;
> -	u64 us_per_frame, fps;
> -	u32 max_rate;
> +	u32 fps, max_rate;
>  
>  	int ret = 0;
>  
> @@ -405,23 +404,19 @@ int iris_venc_s_param(struct iris_inst *inst, struct v4l2_streamparm *s_parm)
>  			timeperframe->denominator = default_rate;
>  	}
>  
> -	us_per_frame = timeperframe->numerator * (u64)USEC_PER_SEC;
> -	do_div(us_per_frame, timeperframe->denominator);
> -
> -	if (!us_per_frame)
> +	fps = timeperframe->numerator / timeperframe->denominator;

This is wrong, should be timeperframe->denominator/timeperframe->numerator
Also I think it would be better to clamp the fps?

Thanks,
Dikshita

> +	if (!fps)
>  		return -EINVAL;
>  
> -	fps = (u64)USEC_PER_SEC;
> -	do_div(fps, us_per_frame);
>  	if (fps > max_rate) {
>  		ret = -ENOMEM;
>  		goto reset_rate;
>  	}
>  
>  	if (is_frame_rate)
> -		inst->frame_rate = (u32)fps;
> +		inst->frame_rate = fps;
>  	else
> -		inst->operating_rate = (u32)fps;
> +		inst->operating_rate = fps;
>  
>  	if ((s_parm->type == V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE && vb2_is_streaming(src_q)) ||
>  	    (s_parm->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE && vb2_is_streaming(dst_q))) {
>