linux-kernel - Re: [PATCH] media: venus: use div64_u64() instead of do

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Date: Tue, 2 Jan 2024 13:19:42 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Himanshu Bhavani <himanshu.bhavani@...iconsignals.io>
Cc: stanimir.k.varbanov@...il.com, quic_vgarodia@...cinc.com, 
	agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org, 
	mchehab@...nel.org, "Bryan O'Donoghue" <bryan.odonoghue@...aro.org>, 
	linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: venus: use div64_u64() instead of do_div()

On Fri, 29 Dec 2023 at 14:16, Himanshu Bhavani
<himanshu.bhavani@...iconsignals.io> wrote:
>
> do_div() does a 64-by-32 division.
> When the divisor is u64, do_div() truncates it to 32 bits, this means it
> can test non-zero and be truncated to zero for division.
>
> fix do_div.cocci warning:
> do_div() does a 64-by-32 division, please consider using div64_u64 instead.
>
> Signed-off-by: Himanshu Bhavani <himanshu.bhavani@...iconsignals.io>
>
> diff --git a/drivers/media/platform/qcom/venus/venc.c b/drivers/media/platform/qcom/venus/venc.c
> index 44b13696cf82..81853eb2993a 100644
> --- a/drivers/media/platform/qcom/venus/venc.c
> +++ b/drivers/media/platform/qcom/venus/venc.c
> @@ -409,13 +409,13 @@ static int venc_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a)
>         out->capability = V4L2_CAP_TIMEPERFRAME;
>
>         us_per_frame = timeperframe->numerator * (u64)USEC_PER_SEC;
> -       do_div(us_per_frame, timeperframe->denominator);
> +       div64_u64(us_per_frame, timeperframe->denominator);

NAK! This is completely incorrect. do_div() is a macro and it changes
the first argument. div64_u64 is a function, which returns the result
instead of changing the first argument.

Please consider checking the code before sending a patch.

>
>         if (!us_per_frame)
>                 return -EINVAL;
>
>         fps = (u64)USEC_PER_SEC;
> -       do_div(fps, us_per_frame);
> +       div64_u64(fps, us_per_frame);
>
>         inst->timeperframe = *timeperframe;
>         inst->fps = fps;
> --
> 2.25.1
>
>


-- 
With best wishes
Dmitry