linux-kernel - Re: [PATCH 3/3] media: iris: Fix fps calculation

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Message-ID: <7mqgcndlrffm2wczev4s5osza7eg44zonqykfmbxq4z62u2rzf@3ugznlbhqwiu>
Date: Sat, 6 Dec 2025 06:06:36 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: 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>,
        Dikshita Agarwal <dikshita.agarwal@....qualcomm.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Bryan O'Donoghue <bod@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        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 3/3] media: iris: Fix fps calculation

On Wed, Dec 03, 2025 at 08:55:36AM +0000, 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 | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/platform/qcom/iris/iris_venc.c b/drivers/media/platform/qcom/iris/iris_venc.c
> index 5830eba93c68b27fa9db87bac63a691eaca338d2..730f2aa1a83b2f4f90227ab9a7e04aee7c2c3cfe 100644
> --- a/drivers/media/platform/qcom/iris/iris_venc.c
> +++ b/drivers/media/platform/qcom/iris/iris_venc.c
> @@ -408,11 +408,10 @@ int iris_venc_s_param(struct iris_inst *inst, struct v4l2_streamparm *s_parm)
>  	us_per_frame = timeperframe->numerator * (u64)USEC_PER_SEC;
>  	do_div(us_per_frame, timeperframe->denominator);
>  
> -	if (!us_per_frame)
> +	if (!us_per_frame || us_per_frame > USEC_PER_SEC)
>  		return -EINVAL;
>  
> -	fps = (u64)USEC_PER_SEC;
> -	do_div(fps, us_per_frame);
> +	fps = USEC_PER_SEC / (u32)us_per_frame;

Can we replace this with:

fps = timeperframe->denominator / timeperframe->numerator ?

>  	if (fps > max_rate) {
>  		ret = -ENOMEM;
>  		goto reset_rate;
> 
> -- 
> 2.52.0.158.g65b55ccf14-goog
> 

-- 
With best wishes
Dmitry