1 files changed, 30 insertions, 0 deletions

diff --git a/kernel/time.c b/kernel/time.c
index 2e2e469a7fec..804798005d19 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -662,6 +662,36 @@ u64 nsec_to_clock_t(u64 x)
 #endif
 }
 
+/**
+ * nsecs_to_jiffies - Convert nsecs in u64 to jiffies
+ *
+ * @n:  nsecs in u64
+ *
+ * Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
+ * And this doesn't return MAX_JIFFY_OFFSET since this function is designed
+ * for scheduler, not for use in device drivers to calculate timeout value.
+ *
+ * note:
+ *   NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
+ *   ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
+ */
+unsigned long nsecs_to_jiffies(u64 n)
+{
+#if (NSEC_PER_SEC % HZ) == 0
+        /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
+        return div_u64(n, NSEC_PER_SEC / HZ);
+#elif (HZ % 512) == 0
+        /* overflow after 292 years if HZ = 1024 */
+        return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
+#else
+        /*
+         * Generic case - optimized for cases where HZ is a multiple of 3.
+         * overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
+         */
+        return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
+#endif
+}
+
 #if (BITS_PER_LONG < 64)
 u64 get_jiffies_64(void)
 {