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

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Message-ID: <0f605226-dd98-addc-eac2-9e3eb36e748a@quicinc.com>
Date: Tue, 2 Jan 2024 11:02:28 +0530
From: Dikshita Agarwal <quic_dikshita@...cinc.com>
To: Himanshu Bhavani <himanshu.bhavani@...iconsignals.io>,
        <stanimir.k.varbanov@...il.com>, <quic_vgarodia@...cinc.com>,
        <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <mchehab@...nel.org>
CC: 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 12/29/2023 5:45 PM, Himanshu Bhavani 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);
I think, this should be like below:
us_per_frame = div64_u64(us_per_frame, timeperframe->denominator);

because do_div does the in-place division while div64_u64 doesn't.
so final value of us_per_frame won't be correct with this change.

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

Thanks,
Dikshita