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

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Message-ID: <CANiDSCvCGX6KaTcVRFvWb=Z8YQNi-Tj5MVp66UjCyH8ZZF5Nmw@mail.gmail.com>
Date: Wed, 10 Dec 2025 16:23:01 +0900
From: Ricardo Ribalda <ribalda@...omium.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
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 Sat, 6 Dec 2025 at 13:06, Dmitry Baryshkov
<dmitry.baryshkov@....qualcomm.com> wrote:
>
> 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 ?

Yep, I believe you are correct

I will send a new version soon.

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



-- 
Ricardo Ribalda