linux-kernel - Re: [PATCH] drm/msm: Avoid rounding up to one jiffy

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Message-ID: <82a53f0a-be0a-4725-9ef9-6ee5388722e1@quicinc.com>
Date: Mon, 13 Jan 2025 16:03:55 +0530
From: Akhil P Oommen <quic_akhilpo@...cinc.com>
To: Rob Clark <robdclark@...il.com>, <dri-devel@...ts.freedesktop.org>
CC: <freedreno@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        "Rob
 Clark" <robdclark@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie
	<airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        open list
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm: Avoid rounding up to one jiffy

On 1/10/2025 4:37 AM, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> If userspace is trying to achieve a timeout of zero, let 'em have it.
> Only round up if the timeout is greater than zero.
> 
> Fixes: 4969bccd5f4e ("drm/msm: Avoid rounding down to zero jiffies")
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/msm/msm_drv.h | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index fee31680a6d5..451d258b9827 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -537,16 +537,14 @@ static inline int align_pitch(int width, int bpp)
>  static inline unsigned long timeout_to_jiffies(const ktime_t *timeout)
>  {
>  	ktime_t now = ktime_get();
> -	s64 remaining_jiffies;
>  
> -	if (ktime_compare(*timeout, now) < 0) {
> -		remaining_jiffies = 0;
> +	if (ktime_compare(*timeout, now) <= 0) {
> +		return 0;
>  	} else {

For readability, we can now remove 'else' block and de-nest rest of the
code.

-Akhil

>  		ktime_t rem = ktime_sub(*timeout, now);
> -		remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
> +		s64 remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
> +		return clamp(remaining_jiffies, 1LL, (s64)INT_MAX);
>  	}
> -
> -	return clamp(remaining_jiffies, 1LL, (s64)INT_MAX);
>  }
>  
>  /* Driver helpers */