printk: Add sleep time to timestamps

cpu_clock() uses monotonic time, which skews when the system suspends,
making it difficult to interpret kmsg timestamps.

Add the sleep time offset to cpu_clock() in order to make kmsg timestamps
reflect the actual boot time.

Signed-off-by: Sultanxda <sultanxda@gmail.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Danny Lin <danny@kdrag0n.dev>
Signed-off-by: Fiqri Ardyansyah <fiqri15072019@gmail.com>
Signed-off-by: Forenche <prahul2003@gmail.com>
Signed-off-by: Cyber Knight <cyberknight755@gmail.com>

Author: kerneltoast

include/linux/timekeeping.h

@@ -347,5 +347,6 @@ extern void read_boot_clock64(struct timespec64 *ts);
 extern int update_persistent_clock(struct timespec now);
 extern int update_persistent_clock64(struct timespec64 now);
 
+s64 get_total_sleep_time_nsec(void);
 
 #endif

kernel/printk/printk.c

@@ -1232,6 +1232,7 @@ static size_t print_time(u64 ts, char *buf)
 	if (!printk_time)
 		return 0;
 
+	ts += get_total_sleep_time_nsec();
 	rem_nsec = do_div(ts, 1000000000);
 
 	if (!buf)

kernel/time/timekeeping.c

@@ -2332,3 +2332,13 @@ void xtime_update(unsigned long ticks)
 	write_sequnlock(&jiffies_lock);
 	update_wall_time();
 }
+
+/**
+ * get_total_sleep_time_nsec() - returns total sleep time in nanoseconds
+ */
+s64 get_total_sleep_time_nsec(void)
+{
+	struct timekeeper *tk = &tk_core.timekeeper;
+
+	return ktime_to_ns(tk->offs_boot);
+}