[U-Boot] [PATCH V4] Nomadik: fix reset_timer()

[Tom Rix <tom@bumblecow.com>]

Alessandro Rubini wrote:
> From: Alessandro Rubini <rubini@unipv.it>
> 
> Previous code was failing when reading back the timer less than
> 400us after resetting it. This lead nand operations to incorrectly
> timeout any now and then.  Moreover, writing the load register isn't
> immediately reflected in the value register. We must wait for a clock
> edge, so read_timer now waits for the value to change at least once,
> otherwise nand operation would timeout anyways (though less frequently).
> 
> 
> Signed-off-by: Alessandro Rubini <rubini@unipv.it>
> Acked-by: Andrea Gallo <andrea.gallo@stericsson.com>
> ---
> 
> I finally managed to test on hardware my V2 and V3, posted on
> 2009-11-06 after a compile check. V2 was the denk-suggested way, while
> V3 was a less invasive proposal, not as bad as my original V1.
> 
> Unfortunately, during my tests another bug appeared: it turns out
> writing to the load register has not really an immediate effect, so
> all of V1 V2 and V3 were all fixing the bigger bug but not very reliable on
> the field.
> 
> This is a respin of V3 that also deals with the unexpected hardware latency.
> 
> 
>  cpu/arm926ejs/nomadik/timer.c |   15 ++++++++++++---
>  1 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/cpu/arm926ejs/nomadik/timer.c b/cpu/arm926ejs/nomadik/timer.c
> index 16067c9..544d438 100644
> --- a/cpu/arm926ejs/nomadik/timer.c
> +++ b/cpu/arm926ejs/nomadik/timer.c
> @@ -34,8 +34,8 @@
>  #define TICKS_PER_HZ		(TIMER_CLOCK / CONFIG_SYS_HZ)
>  #define TICKS_TO_HZ(x)		((x) / TICKS_PER_HZ)
>  
> -/* macro to read the 32 bit timer: since it decrements, we invert read value */
> -#define READ_TIMER() (~readl(CONFIG_SYS_TIMERBASE + MTU_VAL(0)))
> +/* macro to read the decrementing 32 bit timer as an increasing count */
> +#define READ_TIMER() (0 - readl(CONFIG_SYS_TIMERBASE + MTU_VAL(0)))
>  
>  /* Configure a free-running, auto-wrap counter with no prescaler */
>  int timer_init(void)
> @@ -49,7 +49,16 @@ int timer_init(void)
>  /* Restart counting from 0 */
>  void reset_timer(void)
>  {
> -	writel(0, CONFIG_SYS_TIMERBASE + MTU_LR(0)); /* Immediate effect */
> +	ulong val;
> +	writel(0, CONFIG_SYS_TIMERBASE + MTU_LR(0));
> +	/*
> +	 * The load-register isn't really immediate: it changes on clock
> +	 * edges, so we must wait for our newly-written value to appear.
> +	 * Since we might miss reading 0, wait for any change in value.
> +	 */
> +	val = READ_TIMER();
> +	while (READ_TIMER() == val)
> +		;
>  }
>  
>  /* Return how many HZ passed since "base" */
Applied to arm/next
Sorry for the delay.
Tom