[PATCH] kernel/power/hibernate.c: be sure of 'start' is not bigger than 'stop'

[Chen Gang <gang.chen.5i5j@gmail.com>]

For do_div(), it need 'u64' type, which means the outside must be sure
of 'start' is not bigger than 'stop', or it will report warning.

The related warning (with allmodconfig for unicore32):

    CC      kernel/power/hibernate.o
  kernel/power/hibernate.c: In function ‘swsusp_show_speed’:
  kernel/power/hibernate.c:237: warning: comparison of distinct pointer types lacks a cast

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
---
 kernel/power/hibernate.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index f4f2073..0dec9b7 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -228,12 +228,17 @@ static void platform_recover(int platform_mode)
 void swsusp_show_speed(struct timeval *start, struct timeval *stop,
 			unsigned nr_pages, char *msg)
 {
-	s64 elapsed_centisecs64;
+	u64 elapsed_centisecs64;
 	int centisecs;
 	int k;
 	int kps;
 
 	elapsed_centisecs64 = timeval_to_ns(stop) - timeval_to_ns(start);
+	if ((s64)elapsed_centisecs64 < 0) {
+		printk(KERN_ERR "PM: stop: %llu < start %llu\n",
+			timeval_to_ns(stop), timeval_to_ns(start));
+		return;
+	}
 	do_div(elapsed_centisecs64, NSEC_PER_SEC / 100);
 	centisecs = elapsed_centisecs64;
 	if (centisecs == 0)
-- 
1.9.2.459.g68773ac