linux-kernel - Re: [PATCH] clocksource: arch_arm_timer: Fix timecounter initialization

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5398A7B2.6030807@codeaurora.org>
Date:	Wed, 11 Jun 2014 12:02:10 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Xiubo Li <Li.Xiubo@...escale.com>
CC:	daniel.lezcano@...aro.org, tglx@...utronix.de,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Marc Zyngier <Marc.Zyngier@....com>
Subject: Re: [PATCH] clocksource: arch_arm_timer: Fix timecounter initialization

On 06/11/14 01:37, Xiubo Li wrote:
> The third parameter(u64 start_tstamp) of timecounter_init() should
> be the start time by ns, not a cycle counter.
>
> Signed-off-by: Xiubo Li <Li.Xiubo@...escale.com>
> ---
>  drivers/clocksource/arm_arch_timer.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 5163ec1..6c3cfd8 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -426,7 +426,7 @@ struct timecounter *arch_timer_get_timecounter(void)
>  
>  static void __init arch_counter_register(unsigned type)
>  {
> -	u64 start_count;
> +	u64 start_count, start_ns;
>  
>  	/* Register the CP15 based counter if we have one */
>  	if (type & ARCH_CP15_TIMER)
> @@ -438,7 +438,8 @@ static void __init arch_counter_register(unsigned type)
>  	clocksource_register_hz(&clocksource_counter, arch_timer_rate);
>  	cyclecounter.mult = clocksource_counter.mult;
>  	cyclecounter.shift = clocksource_counter.shift;
> -	timecounter_init(&timecounter, &cyclecounter, start_count);
> +	start_ns = cyclecounter_cyc2ns(&cyclecounter, start_count);
> +	timecounter_init(&timecounter, &cyclecounter, start_ns);
>  
>  	/* 56 bits minimum, so we assume worst case rollover */
>  	sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);

This doesn't make much sense. We're converting start_count, which could
be a very large number, into nanoseconds. It looks like we're assuming
the counter always starts at 0 which is not always true if you sit in a
bootloader for a long time. Perhaps it would be better to just do

    timecounter_init(&timecounter, &cyclecounter, 0);

or

    timecounter_init(&timecounter, &cyclecounter,
ktime_to_ns(ktime_get_real()));

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/