linux-kernel - Re: gpu: drm: msm: use div64_u64() instead of do

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Message-ID: <6ea0e85e-1ade-f102-86c2-4b71dbc24285@linaro.org>
Date:   Thu, 10 Feb 2022 01:17:17 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Qing Wang <wangqing@...o.com>, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: gpu: drm: msm: use div64_u64() instead of do_div()

On 09/02/2022 11:37, Qing Wang wrote:
> From: Wang Qing <wangqing@...o.com>
> 
> 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: Wang Qing <wangqing@...o.com>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

> ---
>   drivers/gpu/drm/msm/msm_gpu.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> index 2c1049c..aa4617b
> --- a/drivers/gpu/drm/msm/msm_gpu.c
> +++ b/drivers/gpu/drm/msm/msm_gpu.c
> @@ -648,7 +648,7 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
>   	/* Calculate the clock frequency from the number of CP cycles */
>   	if (elapsed) {
>   		clock = (stats->cpcycles_end - stats->cpcycles_start) * 1000;
> -		do_div(clock, elapsed);
> +		div64_u64(clock, elapsed);
>   	}
>   
>   	trace_msm_gpu_submit_retired(submit, elapsed, clock,


-- 
With best wishes
Dmitry