drm/i915: compute wait_ioctl timeout correctly

We've lost the +1 required for correct timeouts in

commit 5ed0bdf21a85d78e04f89f15ccf227562177cbd9
Author: Thomas Gleixner <tglx@linutronix.de>
Date:   Wed Jul 16 21:05:06 2014 +0000

    drm: i915: Use nsec based interfaces

    Use ktime_get_raw_ns() and get rid of the back and forth timespec
    conversions.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: John Stultz <john.stultz@linaro.org>

So fix this up by reinstating our handrolled _timeout function. While
at it bother with handling MAX_JIFFIES.

v2: Convert to usecs (we don't care about the accuracy anyway) first
to avoid overflow issues Dave Gordon spotted.

v3: Drop the explicit MAX_JIFFY_OFFSET check, usecs_to_jiffies should
take care of that already. It might be a bit too enthusiastic about it
though.

v4: Chris has a much nicer color, so use his implementation.

This requires to export nsec_to_jiffies from time.c.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dave Gordon <david.s.gordon@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=82749
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/i915_drv.h

@@ -3032,6 +3032,11 @@ static inline unsigned long msecs_to_jiffies_timeout(const unsigned int m)
 	return min_t(unsigned long, MAX_JIFFY_OFFSET, j + 1);
 }
 
+static inline unsigned long nsecs_to_jiffies_timeout(const u64 n)
+{
+        return min_t(u64, MAX_JIFFY_OFFSET, nsecs_to_jiffies64(n) + 1);
+}
+
 static inline unsigned long
 timespec_to_jiffies_timeout(const struct timespec *value)
 {

drivers/gpu/drm/i915/i915_gem.c

@@ -1227,7 +1227,8 @@ int __i915_wait_seqno(struct intel_engine_cs *ring, u32 seqno,
 	if (i915_seqno_passed(ring->get_seqno(ring, true), seqno))
 		return 0;
 
-	timeout_expire = timeout ? jiffies + nsecs_to_jiffies((u64)*timeout) : 0;
+	timeout_expire = timeout ?
+		jiffies + nsecs_to_jiffies_timeout((u64)*timeout) : 0;
 
 	if (INTEL_INFO(dev)->gen >= 6 && ring->id == RCS && can_wait_boost(file_priv)) {
 		gen6_rps_boost(dev_priv);

kernel/time/time.c

@@ -745,6 +745,7 @@ u64 nsecs_to_jiffies64(u64 n)
 	return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
 #endif
 }
+EXPORT_SYMBOL(nsecs_to_jiffies64);
 
 /**
  * nsecs_to_jiffies - Convert nsecs in u64 to jiffies