From: khilman@deeprootsystems•com (Kevin Hilman)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH V2] ARM: OMAP: counter: add locking to read_persistent_clock
Date: Mon, 24 Sep 2012 17:43:21 -0700 [thread overview]
Message-ID: <87d31bj5jq.fsf@deeprootsystems.com> (raw)
In-Reply-To: <1347434081-11469-1-git-send-email-r.sricharan@ti.com> (R. Sricharan's message of "Wed, 12 Sep 2012 12:44:41 +0530")
R Sricharan <r.sricharan@ti•com> writes:
> From: Colin Cross <ccross@android•com>
>
> read_persistent_clock uses a global variable, use a spinlock to
> ensure non-atomic updates to the variable don't overlap and cause
> time to move backwards.
>
> Signed-off-by: Colin Cross <ccross@android•com>
> Signed-off-by: R Sricharan <r.sricharan@ti•com>
Acked-by: Kevin Hilman <khilman@ti•com>
Tony, this should probably be queued up for v3.7-rc and flagged for stable.
Thanks,
Kevin
> ---
> [V2] Added signed-off-by and looped in "linux-arm-kernel" list
>
> arch/arm/plat-omap/counter_32k.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm/plat-omap/counter_32k.c b/arch/arm/plat-omap/counter_32k.c
> index dbf1e03..2bc51fb 100644
> --- a/arch/arm/plat-omap/counter_32k.c
> +++ b/arch/arm/plat-omap/counter_32k.c
> @@ -55,22 +55,29 @@ static u32 notrace omap_32k_read_sched_clock(void)
> * nsecs and adds to a monotonically increasing timespec.
> */
> static struct timespec persistent_ts;
> -static cycles_t cycles, last_cycles;
> +static cycles_t cycles;
> static unsigned int persistent_mult, persistent_shift;
> +static DEFINE_SPINLOCK(read_persistent_clock_lock);
> +
> static void omap_read_persistent_clock(struct timespec *ts)
> {
> unsigned long long nsecs;
> - cycles_t delta;
> - struct timespec *tsp = &persistent_ts;
> + cycles_t last_cycles;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&read_persistent_clock_lock, flags);
>
> last_cycles = cycles;
> cycles = sync32k_cnt_reg ? __raw_readl(sync32k_cnt_reg) : 0;
> - delta = cycles - last_cycles;
>
> - nsecs = clocksource_cyc2ns(delta, persistent_mult, persistent_shift);
> + nsecs = clocksource_cyc2ns(cycles - last_cycles,
> + persistent_mult, persistent_shift);
> +
> + timespec_add_ns(&persistent_ts, nsecs);
> +
> + *ts = persistent_ts;
>
> - timespec_add_ns(tsp, nsecs);
> - *ts = *tsp;
> + spin_unlock_irqrestore(&read_persistent_clock_lock, flags);
> }
>
> /**
next prev parent reply other threads:[~2012-09-25 0:43 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-12 7:14 [PATCH V2] ARM: OMAP: counter: add locking to read_persistent_clock R Sricharan
2012-09-25 0:43 ` Kevin Hilman [this message]
2012-09-25 1:22 ` Tony Lindgren
2012-09-25 7:43 ` R, Sricharan
2012-09-25 15:17 ` Tony Lindgren
2012-10-08 21:02 ` Tony Lindgren
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