[U-Boot] [PATCH 1/9] Exynos: Change get_timer() to work correctly

[Simon Glass <sjg@chromium.org>]

On Wed, Feb 27, 2013 at 2:02 AM, Akshay Saraswat <akshay.s@samsung.com> wrote:
> At present get_timer() does not return sane values. It should count up
> smoothly in milliscond intervals.
>
> We can change the PWM to count down at 1MHz, providing a resolution
> of 1us and a range of about an hour between required get_timer() calls.
>
> TEST=sf probe 1:0; time sf read 40008000 0 1000
> Try with different numbers of bytes and see that sane values are obtained
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>

Acked-by: Simon Glass <sjg@chromium.org>

> ---
>  arch/arm/cpu/armv7/s5p-common/pwm.c   |   6 ++
>  arch/arm/cpu/armv7/s5p-common/timer.c | 100 +++++++++++++---------------------
>  2 files changed, 44 insertions(+), 62 deletions(-)
>
> diff --git a/arch/arm/cpu/armv7/s5p-common/pwm.c b/arch/arm/cpu/armv7/s5p-common/pwm.c
> index 44d7bc3..3147f59 100644
> --- a/arch/arm/cpu/armv7/s5p-common/pwm.c
> +++ b/arch/arm/cpu/armv7/s5p-common/pwm.c
> @@ -174,6 +174,12 @@ int pwm_init(int pwm_id, int div, int invert)
>
>         /* set count value */
>         offset = pwm_id * 3;
> +
> +       /*
> +        * TODO(sjg): Use this as a countdown timer for now. We count down
> +        * from the maximum value to 0, then reset.
> +        */
> +       timer_rate_hz = -1;
>         writel(timer_rate_hz, &pwm->tcntb0 + offset);
>
>         val = readl(&pwm->tcon) & ~(0xf << TCON_OFFSET(pwm_id));
> diff --git a/arch/arm/cpu/armv7/s5p-common/timer.c b/arch/arm/cpu/armv7/s5p-common/timer.c
> index e78c716..c48a297 100644
> --- a/arch/arm/cpu/armv7/s5p-common/timer.c
> +++ b/arch/arm/cpu/armv7/s5p-common/timer.c
> @@ -39,13 +39,33 @@ static inline struct s5p_timer *s5p_get_base_timer(void)
>         return (struct s5p_timer *)samsung_get_base_timer();
>  }
>
> +/**
> + * Read the countdown timer.
> + *
> + * This operates at 1MHz and counts downwards. It will wrap about every
> + * hour (2^32 microseconds).
> + *
> + * @return current value of timer
> + */
> +static unsigned long timer_get_us_down(void)
> +{
> +       struct s5p_timer *const timer = s5p_get_base_timer();
> +
> +       return readl(&timer->tcnto4);
> +}
> +
>  int timer_init(void)
>  {
>         /* PWM Timer 4 */
> -       pwm_init(4, MUX_DIV_2, 0);
> +       pwm_init(4, MUX_DIV_4, 0);
>         pwm_config(4, 0, 0);
>         pwm_enable(4);
>
> +       /* Use this as the current monotonic time in us */
> +       gd->arch.timer_reset_value = 0;
> +
> +       /* Use this as the last timer value we saw */
> +       gd->arch.lastinc = timer_get_us_down();
>         reset_timer_masked();
>
>         return 0;
> @@ -56,48 +76,28 @@ int timer_init(void)
>   */
>  unsigned long get_timer(unsigned long base)
>  {
> -       return get_timer_masked() - base;
> +       ulong now = timer_get_us_down();
> +
> +       /*
> +        * Increment the time by the amount elapsed since the last read.
> +        * The timer may have wrapped around, but it makes no difference to
> +        * our arithmetic here.
> +        */
> +       gd->arch.timer_reset_value += gd->arch.lastinc - now;
> +       gd->arch.lastinc = now;
> +
> +       /* Divide by 1000 to convert from us to ms */
> +       return gd->arch.timer_reset_value / 1000 - base;
>  }
>
>  /* delay x useconds */
>  void __udelay(unsigned long usec)
>  {
> -       struct s5p_timer *const timer = s5p_get_base_timer();
> -       unsigned long tmo, tmp, count_value;
> -
> -       count_value = readl(&timer->tcntb4);
> -
> -       if (usec >= 1000) {
> -               /*
> -                * if "big" number, spread normalization
> -                * to seconds
> -                * 1. start to normalize for usec to ticks per sec
> -                * 2. find number of "ticks" to wait to achieve target
> -                * 3. finish normalize.
> -                */
> -               tmo = usec / 1000;
> -               tmo *= (CONFIG_SYS_HZ * count_value);
> -               tmo /= 1000;
> -       } else {
> -               /* else small number, don't kill it prior to HZ multiply */
> -               tmo = usec * CONFIG_SYS_HZ * count_value;
> -               tmo /= (1000 * 1000);
> -       }
> -
> -       /* get current timestamp */
> -       tmp = get_current_tick();
> -
> -       /* if setting this fordward will roll time stamp */
> -       /* reset "advancing" timestamp to 0, set lastinc value */
> -       /* else, set advancing stamp wake up time */
> -       if ((tmo + tmp + 1) < tmp)
> -               reset_timer_masked();
> -       else
> -               tmo += tmp;
> -
> -       /* loop till event */
> -       while (get_current_tick() < tmo)
> -               ;       /* nop */
> +       unsigned long count_value;
> +
> +       count_value = timer_get_us_down();
> +       while ((int)(count_value - timer_get_us_down()) < (int)usec)
> +               ;
>  }
>
>  void reset_timer_masked(void)
> @@ -109,30 +109,6 @@ void reset_timer_masked(void)
>         gd->arch.tbl = 0;
>  }
>
> -unsigned long get_timer_masked(void)
> -{
> -       struct s5p_timer *const timer = s5p_get_base_timer();
> -       unsigned long count_value = readl(&timer->tcntb4);
> -
> -       return get_current_tick() / count_value;
> -}
> -
> -unsigned long get_current_tick(void)
> -{
> -       struct s5p_timer *const timer = s5p_get_base_timer();
> -       unsigned long now = readl(&timer->tcnto4);
> -       unsigned long count_value = readl(&timer->tcntb4);
> -
> -       if (gd->arch.lastinc >= now)
> -               gd->arch.tbl += gd->arch.lastinc - now;
> -       else
> -               gd->arch.tbl += gd->arch.lastinc + count_value - now;
> -
> -       gd->arch.lastinc = now;
> -
> -       return gd->arch.tbl;
> -}
> -
>  /*
>   * This function is derived from PowerPC code (read timebase as long long).
>   * On ARM it just returns the timer value.
> --
> 1.8.0
>