[PATCH] time: Introduce jiffies64_to_msecs()

[Li RongQing]

there is a similar helper in net/netfilter/nf_tables_api.c,
this maybe become a common request someday.

and avoid to call div_64 at some condition

Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
---
 include/linux/jiffies.h |  1 +
 kernel/time/time.c      | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index fa928242567d..1b6d31da7cbc 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -297,6 +297,7 @@ static inline u64 jiffies_to_nsecs(const unsigned long j)
 }
 
 extern u64 jiffies64_to_nsecs(u64 j);
+extern u64 jiffies64_to_msecs(u64 j);
 
 extern unsigned long __msecs_to_jiffies(const unsigned int m);
 #if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 2edb5088a70b..0083eb711fb7 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -719,6 +719,16 @@ u64 jiffies64_to_nsecs(u64 j)
 }
 EXPORT_SYMBOL(jiffies64_to_nsecs);
 
+u64 jiffies64_to_msecs(const u64 j)
+{
+#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
+	return (MSEC_PER_SEC / HZ) * j;
+#else
+	return div_u64(j * HZ_TO_MSEC_NUM, HZ_TO_MSEC_DEN);
+#endif
+}
+EXPORT_SYMBOL(jiffies64_to_msecs);
+
 /**
  * nsecs_to_jiffies64 - Convert nsecs in u64 to jiffies64
  *
-- 
2.16.2