Subject: [PATCH 2/2] clocksource: armada-370-xp: Use atomic access for shared registers

From: [email-masked] (Daniel Lezcano)
Date: Thu, 20 Feb 2014 08:59:34 +0100

On 02/19/2014 09:05 PM, Ezequiel Garcia wrote:
> Replace the driver-specific thread-safe shared register API
> by the recently introduced atomic_io_clear_set().

Hi Ezequiel,

AFAICS, the code is lockless, your change adds a lock.

What race is it supposed to fix ?

> Signed-off-by: Ezequiel Garcia <[email-masked]>
> ---
>   drivers/clocksource/time-armada-370-xp.c | 12 ++++--------
>   1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/clocksource/time-armada-370-xp.c b/drivers/clocksource/time-armada-370-xp.c
> index ee8691b..0451e62 100644
> --- a/drivers/clocksource/time-armada-370-xp.c
> +++ b/drivers/clocksource/time-armada-370-xp.c
> @@ -85,12 +85,6 @@ static u32 ticks_per_jiffy;
>
>   static struct clock_event_device __percpu *armada_370_xp_evt;
>
> -static void timer_ctrl_clrset(u32 clr, u32 set)
> -{
> -	writel((readl(timer_base + TIMER_CTRL_OFF) & ~clr) | set,
> -		timer_base + TIMER_CTRL_OFF);
> -}
> -
>   static void local_timer_ctrl_clrset(u32 clr, u32 set)
>   {
>   	writel((readl(local_base + TIMER_CTRL_OFF) & ~clr) | set,
> @@ -245,7 +239,7 @@ static void __init armada_370_xp_timer_common_init(struct device_node *np)
>   		clr = TIMER0_25MHZ;
>   		enable_mask = TIMER0_EN | TIMER0_DIV(TIMER_DIVIDER_SHIFT);
>   	}
> -	timer_ctrl_clrset(clr, set);
> +	atomic_io_modify(timer_base + TIMER_CTRL_OFF, clr | set, set);
>   	local_timer_ctrl_clrset(clr, set);
>
>   	/*
> @@ -263,7 +257,9 @@ static void __init armada_370_xp_timer_common_init(struct device_node *np)
>   	writel(0xffffffff, timer_base + TIMER0_VAL_OFF);
>   	writel(0xffffffff, timer_base + TIMER0_RELOAD_OFF);
>
> -	timer_ctrl_clrset(0, TIMER0_RELOAD_EN | enable_mask);
> +	atomic_io_modify(timer_base + TIMER_CTRL_OFF,
> +		TIMER0_RELOAD_EN | enable_mask,
> +		TIMER0_RELOAD_EN | enable_mask);
>
>   	/*
>   	 * Set scale and timer for sched_clock.
>

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