On Fri, Jul 29, 2016 at 2:50 AM, Bogdan Mirea <[email protected]> wrote: > This option enables Boot Time Preservation between Bootloader and > Linux Kernel. It is based on the idea that the Bootloader (or any > other early firmware) will start the HW Timer and Linux Kernel will > count the time starting with the cycles elapsed since timer start. > > Signed-off-by: Bogdan Mirea <[email protected]> > --- > kernel/time/Kconfig | 8 ++++++++ > kernel/time/sched_clock.c | 6 ++++++ > 2 files changed, 14 insertions(+) > > diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig > index 4008d9f..d001839 100644 > --- a/kernel/time/Kconfig > +++ b/kernel/time/Kconfig > @@ -193,5 +193,13 @@ config HIGH_RES_TIMERS > hardware is not capable then this option only increases > the size of the kernel image. > > +config BOOT_TIME_PRESERVE > + bool "Preserve Boot Time Support" > + help > + This option enables Boot Time Preservation between Bootloader and > + Linux Kernel. It is based on the idea that the Bootloader (or any > + other early firmware) will start the HW Timer and Linux Kernel will > + count the time starting with the cycles elapsed since timer start. > + > endmenu > endif > diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c > index a26036d..1d6e35a 100644 > --- a/kernel/time/sched_clock.c > +++ b/kernel/time/sched_clock.c > @@ -193,7 +193,13 @@ sched_clock_register(u64 (*read)(void), int bits, > unsigned long rate) > /* Update epoch for new counter and update 'epoch_ns' from old > counter*/ > new_epoch = read(); > cyc = cd.actual_read_sched_clock(); > + > +#ifdef CONFIG_BOOT_TIME_PRESERVE > + ns = rd.epoch_ns + cyc_to_ns((new_epoch - rd.epoch_cyc) & new_mask, > new_mult, new_shift); > +#else > ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & > rd.sched_clock_mask, rd.mult, rd.shift); > +#endif /* CONFIG_BOOT_TIME_PRESERVE */ > +
So... we already have the read_boot_clock64() interface which platforms can define to provide the power-on-to-now delta which the timekeeping logic will make use of at init to initialize the monotonic clock. Is there some reason that interface can't be used here? thanks -john
