read_boot_clock64() returns time of when system was started. Now, that early boot clock is going to be available on x86 it is possible to implement x86 specific version of read_boot_clock64() that takes advantage of this new feature.
Signed-off-by: Pavel Tatashin <pasha.tatas...@oracle.com> --- arch/x86/kernel/time.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c index 774ebafa97c4..32dff35719d9 100644 --- a/arch/x86/kernel/time.c +++ b/arch/x86/kernel/time.c @@ -15,6 +15,7 @@ #include <linux/i8253.h> #include <linux/time.h> #include <linux/export.h> +#include <linux/sched/clock.h> #include <asm/vsyscall.h> #include <asm/x86_init.h> @@ -104,3 +105,32 @@ void __init time_init(void) { late_time_init = x86_late_time_init; } + +/* + * Called once during to boot to initialize boot time. + * This function returns timestamp in timespec format which is sec/nsec from + * epoch of when boot started. + * We use sched_clock_cpu() that gives us nanoseconds from when this clock has + * been started and it happens quiet early during boot process. To calculate + * offset from epoch we use information provided in 'now' by the caller + * + * If sched_clock_cpu() is not available or if there is any kind of error + * i.e. time from epoch is smaller than boot time, we must return zeros in ts, + * and the caller will take care of the error: by assuming that the time when + * this function was called is the beginning of boot time. + */ +void __init read_boot_clock64(struct timespec64 *now, struct timespec64 *ts) +{ + u64 ns_boot = sched_clock_cpu(smp_processor_id()); + bool valid_clock; + u64 ns_now; + + ns_now = timespec64_to_ns(now); + valid_clock = ns_boot && timespec64_valid_strict(now) && + (ns_now > ns_boot); + + if (!valid_clock) + *ts = (struct timespec64){0, 0}; + else + *ts = ns_to_timespec64(ns_now - ns_boot); +} -- 2.16.1