linux-kernel - Re: [PATCH v8 2/6] time: sync read_boot

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Date:   Mon, 13 Nov 2017 11:47:41 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        <steven.sistare@...cle.com>, <daniel.m.jordan@...cle.com>,
        <linux@...linux.org.uk>, <schwidefsky@...ibm.com>,
        <heiko.carstens@...ibm.com>, <john.stultz@...aro.org>,
        <sboyd@...eaurora.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
        <tglx@...utronix.de>, <hpa@...or.com>
Subject: Re: [PATCH v8 2/6] time: sync read_boot_clock64() with persistent
 clock

Hi Pavel,

At 11/09/2017 11:01 AM, Pavel Tatashin wrote:
> read_boot_clock64() returns a boot start timestamp from epoch. Some arches
> may need to access the persistent clock interface in order to calculate the
> epoch offset. The resolution of the persistent clock, however, might be
> low.  Therefore, in order to avoid time discrepancies a new argument 'now'
> is added to read_boot_clock64() parameters. Arch may decide to use it
> instead of accessing persistent clock again.
>
> Also, change read_boot_clock64() to have __init prototype since it is
> accessed only during boot.
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
> ---
>  arch/arm/kernel/time.c      | 2 +-
>  arch/s390/kernel/time.c     | 2 +-
>  include/linux/timekeeping.h | 7 +++----
>  kernel/time/timekeeping.c   | 8 ++++++--
>  4 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm/kernel/time.c b/arch/arm/kernel/time.c
> index 629f8e9981f1..5b259261a268 100644
> --- a/arch/arm/kernel/time.c
> +++ b/arch/arm/kernel/time.c
> @@ -90,7 +90,7 @@ void read_persistent_clock64(struct timespec64 *ts)
>  	__read_persistent_clock(ts);
>  }
>
> -void read_boot_clock64(struct timespec64 *ts)
> +void __init read_boot_clock64(struct timespec64 *now, struct timespec64 *ts)
>  {
>  	__read_boot_clock(ts);
>  }
> diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
> index 5cbd52169348..780b770e6a89 100644
> --- a/arch/s390/kernel/time.c
> +++ b/arch/s390/kernel/time.c
> @@ -220,7 +220,7 @@ void read_persistent_clock64(struct timespec64 *ts)
>  	ext_to_timespec64(clk, ts);
>  }
>
> -void read_boot_clock64(struct timespec64 *ts)
> +void __init read_boot_clock64(struct timespec64 *now, struct timespec64 *ts)
>  {
>  	unsigned char clk[STORE_CLOCK_EXT_SIZE];
>  	__u64 delta;
> diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
> index c198ab40c04f..73919982045e 100644
> --- a/include/linux/timekeeping.h
> +++ b/include/linux/timekeeping.h
> @@ -211,9 +211,8 @@ extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
>   */
>  extern int persistent_clock_is_local;
>
> -extern void read_persistent_clock64(struct timespec64 *ts);
> -extern void read_boot_clock64(struct timespec64 *ts);
> -extern int update_persistent_clock64(struct timespec64 now);
> -
> +void read_persistent_clock64(struct timespec64 *ts);
> +void read_boot_clock64(struct timespec64 *now, struct timespec64 *ts);
> +int update_persistent_clock64(struct timespec64 now);
>

why we should remove the *extern* keyword?

Thanks,
	dou.