[U-Boot] [PATCH 3/9] Exynos: pwm: Fix two bugs in the exynos pwm configuration code

[Simon Glass]

On Wed, Feb 27, 2013 at 2:02 AM, Akshay Saraswat <akshay.s at samsung.com> wrote:
> First, the "div" value was being used incorrectly to compute the frequency of
> the PWM timer. The value passed in is a constant which reflects the value
> that would be found in a configuration register, 0 to 4. That should
> correspond to a scaling factor of 1, 2, 4, 8, or 16, 1 << div, but div + 1 was
> being used instead.
>
> Second, the reset value of the timers were being calculated to give an overall
> frequency, thrown out, and set to a maximum value. This was done so that PWM 4
> could be used as the system clock by counting down from a high value, but it
> was applied indiscriminantly. It should at most be applied only to PWM 4.
>
> This change also takes the opportunity to tidy up the pwm_init function.
>
> TEST=sf probe 1:0; time sf read 40008000 0 1000
> Try with different numbers of bytes and see that sane values are obtained
> Build and boot U-boot with this patch, backlight works properly.
>
> Signed-off-by: Gabe Black <gabeblack at google.com>
> Signed-off-by: Akshay Saraswat <akshay.s at samsung.com>

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

If you redo this patch, I suggest you remove the TODOs.

> ---
>  arch/arm/cpu/armv7/s5p-common/pwm.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm/cpu/armv7/s5p-common/pwm.c b/arch/arm/cpu/armv7/s5p-common/pwm.c
> index 3147f59..02156d1 100644
> --- a/arch/arm/cpu/armv7/s5p-common/pwm.c
> +++ b/arch/arm/cpu/armv7/s5p-common/pwm.c
> @@ -143,7 +143,7 @@ int pwm_init(int pwm_id, int div, int invert)
>         u32 val;
>         const struct s5p_timer *pwm =
>                         (struct s5p_timer *)samsung_get_base_timer();
> -       unsigned long timer_rate_hz;
> +       unsigned long ticks_per_period;
>         unsigned int offset, prescaler;
>
>         /*
> @@ -167,20 +167,24 @@ int pwm_init(int pwm_id, int div, int invert)
>         val |= (div & 0xf) << MUX_DIV_SHIFT(pwm_id);
>         writel(val, &pwm->tcfg1);
>
> -       timer_rate_hz = get_pwm_clk() / ((prescaler + 1) *
> -                       (div + 1));
> +       if (pwm_id == 4) {
> +               /*
> +                * TODO(sjg): Use this as a countdown timer for now. We count
> +                * down from the maximum value to 0, then reset.
> +                */
> +               ticks_per_period = -1UL;
> +       } else {
> +               const unsigned long pwm_hz = 1000;
> +               unsigned long timer_rate_hz = get_pwm_clk() /
> +                       ((prescaler + 1) * (1 << div));
>
> -       timer_rate_hz = timer_rate_hz / CONFIG_SYS_HZ;
> +               ticks_per_period = timer_rate_hz / pwm_hz;
> +       }
>
>         /* 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);
> +       writel(ticks_per_period, &pwm->tcntb0 + offset);
>
>         val = readl(&pwm->tcon) & ~(0xf << TCON_OFFSET(pwm_id));
>         if (invert && (pwm_id < 4))
> --
> 1.8.0
>