linux-kernel - [PATCH v2] drm/msm: Avoid rounding up to one jiffy

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Message-ID: <20250113154841.129521-1-robdclark@gmail.com>
Date: Mon, 13 Jan 2025 07:48:41 -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 v2] 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 | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index fee31680a6d5..a65077855201 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -537,15 +537,12 @@ 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;
-	} else {
-		ktime_t rem = ktime_sub(*timeout, now);
-		remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
-	}
+	if (ktime_compare(*timeout, now) <= 0)
+		return 0;
 
+	ktime_t rem = ktime_sub(*timeout, now);
+	s64 remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
 	return clamp(remaining_jiffies, 1LL, (s64)INT_MAX);
 }
 
-- 
2.47.1