From: Russell King <rmk+kernel@armlinux.org.uk>
Date: Tue, 20 Feb 2018 10:22:22 +0100
Subject: drm/etnaviv: correct timeout calculation
Git-commit: d066b246d482f69553e58d52f746377ce3966b66
Patch-mainline: v4.18-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

The old way did clamp the jiffy conversion and thus caused the timeouts
to become negative after some time. Also it didn't work with userspace
which actually fills the upper 32bits of the 64bit timestamp value.

clock_gettime() is 32-bit on 32-bit architectures. Using 64-bit timespec
math, like we do in this commit, means that when a wrap occurs, the
specified timeout goes into the past and we can't request a timeout in
the future. As the Linux implementation of CLOCK_MONOTONIC is reasonable
and starts at 0, the first such timer wrap will occur after approx. 68
years of system uptime.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/etnaviv/etnaviv_drv.h |   27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

--- a/drivers/gpu/drm/etnaviv/etnaviv_drv.h
+++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.h
@@ -26,6 +26,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/slab.h>
 #include <linux/list.h>
+#include <linux/time64.h>
 #include <linux/types.h>
 #include <linux/sizes.h>
 
@@ -132,19 +133,27 @@ static inline bool fence_after_eq(u32 a,
 	return (s32)(a - b) >= 0;
 }
 
+/*
+ * Etnaviv timeouts are specified wrt CLOCK_MONOTONIC, not jiffies.
+ * We need to calculate the timeout in terms of number of jiffies
+ * between the specified timeout and the current CLOCK_MONOTONIC time.
+ */
 static inline unsigned long etnaviv_timeout_to_jiffies(
 	const struct timespec *timeout)
 {
-	unsigned long timeout_jiffies = timespec_to_jiffies(timeout);
-	unsigned long start_jiffies = jiffies;
-	unsigned long remaining_jiffies;
-
-	if (time_after(start_jiffies, timeout_jiffies))
-		remaining_jiffies = 0;
-	else
-		remaining_jiffies = timeout_jiffies - start_jiffies;
+	struct timespec64 ts, to;
+
+	to = timespec_to_timespec64(*timeout);
+
+	ktime_get_ts64(&ts);
+
+	/* timeouts before "now" have already expired */
+	if (timespec64_compare(&to, &ts) <= 0)
+		return 0;
+
+	ts = timespec64_sub(to, ts);
 
-	return remaining_jiffies;
+	return timespec64_to_jiffies(&ts);
 }
 
 #endif /* __ETNAVIV_DRV_H__ */