Re: [PATCH v2 02/15] clocksource: orion: Use atomic access for shared registers

[Daniel Lezcano <daniel.lezcano-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On 01/21/2014 10:12 AM, Ezequiel Garcia wrote:
> Replace the driver-specific thread-safe shared register API
> by the recently introduced atomic_io_clear_set().
>
> Signed-off-by: Ezequiel Garcia <ezequiel.garcia-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>

Hi Ezequiel,

in the future, put me in Cc when modifying files in clocksource that 
will make my life easier to track the changes.

Thanks.
   -- Daniel

> ---
>   drivers/clocksource/time-orion.c | 28 ++++++++++------------------
>   1 file changed, 10 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/clocksource/time-orion.c b/drivers/clocksource/time-orion.c
> index 9c7f018..3f14e56 100644
> --- a/drivers/clocksource/time-orion.c
> +++ b/drivers/clocksource/time-orion.c
> @@ -35,20 +35,6 @@
>   #define ORION_ONESHOT_MAX	0xfffffffe
>
>   static void __iomem *timer_base;
> -static DEFINE_SPINLOCK(timer_ctrl_lock);
> -
> -/*
> - * Thread-safe access to TIMER_CTRL register
> - * (shared with watchdog timer)
> - */
> -void orion_timer_ctrl_clrset(u32 clr, u32 set)
> -{
> -	spin_lock(&timer_ctrl_lock);
> -	writel((readl(timer_base + TIMER_CTRL) & ~clr) | set,
> -		timer_base + TIMER_CTRL);
> -	spin_unlock(&timer_ctrl_lock);
> -}
> -EXPORT_SYMBOL(orion_timer_ctrl_clrset);
>   /*
>    * Free-running clocksource handling.
> @@ -68,7 +54,8 @@ static int orion_clkevt_next_event(unsigned long delta,
>   {
>   	/* setup and enable one-shot timer */
>   	writel(delta, timer_base + TIMER1_VAL);
> -	orion_timer_ctrl_clrset(TIMER1_RELOAD_EN, TIMER1_EN);
> +	atomic_io_modify(timer_base + TIMER_CTRL,
> +		TIMER1_RELOAD_EN | TIMER1_EN, TIMER1_EN);

I am not convinced this change is worth.

Could you elaborate the race the spinlock should prevent ?

>
>   	return 0;
>   }
> @@ -80,10 +67,13 @@ static void orion_clkevt_mode(enum clock_event_mode mode,
>   		/* setup and enable periodic timer at 1/HZ intervals */
>   		writel(ticks_per_jiffy - 1, timer_base + TIMER1_RELOAD);
>   		writel(ticks_per_jiffy - 1, timer_base + TIMER1_VAL);
> -		orion_timer_ctrl_clrset(0, TIMER1_RELOAD_EN | TIMER1_EN);
> +		atomic_io_modify(timer_base + TIMER_CTRL,
> +			TIMER1_RELOAD_EN | TIMER1_EN,
> +			TIMER1_RELOAD_EN | TIMER1_EN);
>   	} else {
>   		/* disable timer */
> -		orion_timer_ctrl_clrset(TIMER1_RELOAD_EN | TIMER1_EN, 0);
> +		atomic_io_modify(timer_base + TIMER_CTRL,
> +			TIMER1_RELOAD_EN | TIMER1_EN, 0);
>   	}
>   }
>
> @@ -131,7 +121,9 @@ static void __init orion_timer_init(struct device_node *np)
>   	/* setup timer0 as free-running clocksource */
>   	writel(~0, timer_base + TIMER0_VAL);
>   	writel(~0, timer_base + TIMER0_RELOAD);
> -	orion_timer_ctrl_clrset(0, TIMER0_RELOAD_EN | TIMER0_EN);
> +	atomic_io_modify(timer_base + TIMER_CTRL,
> +		TIMER0_RELOAD_EN | TIMER0_EN,
> +		TIMER0_RELOAD_EN | TIMER0_EN);
>   	clocksource_mmio_init(timer_base + TIMER0_VAL, "orion_clocksource",
>   			      clk_get_rate(clk), 300, 32,
>   			      clocksource_mmio_readl_down);
>


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