[U-Boot] [PATCH 1/9 v2] Exynos: Change get_timer() to work correctly

[Minkyu Kang]

Dear Akshay,

On 28/02/13 19:59, Akshay Saraswat 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 with command "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 at chromium.org>
> Signed-off-by: Akshay Saraswat <akshay.s at samsung.com>
> Acked-by: Simon Glass <sjg at chromium.org>
> ---
> Changes since v1:
>         - Added "Acked-by: Simon Glass".
> 
>  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;

is it workaround?

>  	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);

There are special reason to change the div value?
Please let me know.

>  	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)

why convert to int?

> +		;
>  }
>  
>  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.
> 

Thanks,
Minkyu Kang.