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

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Message-ID: <20250109230734.8111-1-robdclark@gmail.com>
Date: Thu,  9 Jan 2025 15:07:33 -0800
From: Rob Clark <robdclark@...il.com>
To: dri-devel@...ts.freedesktop.org
Cc: freedreno@...ts.freedesktop.org,
	linux-arm-msm@...r.kernel.org,
	Rob Clark <robdclark@...omium.org>,
	Rob Clark <robdclark@...il.com>,
	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>,
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm/msm: Avoid rounding up to one jiffy

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 {
 		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 */
-- 
2.47.1