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

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Message-ID: <CANiDSCt2+jqrcTEFXk+Qx4hv7XE2ReSdojGFdLgVOoOM9LKw9w@mail.gmail.com>
Date: Tue, 23 Dec 2025 10:57:16 +0100
From: Ricardo Ribalda <ribalda@...omium.org>
To: Dikshita Agarwal <dikshita.agarwal@....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>, 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 v2 2/2] media: iris: Fix fps calculation

On Tue, 23 Dec 2025 at 10:39, Dikshita Agarwal
<dikshita.agarwal@....qualcomm.com> wrote:
>
>
>
> 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

Ups, sorry about that :S

> Also I think it would be better to clamp the fps?

Do you mean clamp instead of returning -ENOMEM? I have no strong
opinion about that, but I believe that should be a follow up patch.

>
> 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))) {
> >



-- 
Ricardo Ribalda