[U-Boot] [PATCH V4] Nomadik: fix reset_timer()
tom at bumblecow.com
Sat Mar 27 22:09:19 CET 2010
Alessandro Rubini wrote:
> From: Alessandro Rubini <rubini at 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 at unipv.it>
> Acked-by: Andrea Gallo <andrea.gallo at 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.
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