Dear Akshay,
On 28/02/13 19:59, Akshay Saraswat 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 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
> Build and boot U-boot with this patch, backlight works properly.
>
> Signed-off-by: Gabe Black <gabebl...@google.com>
> Signed-off-by: Akshay Saraswat <aksha...@samsung.com>
> Acked-by: Simon Glass <s...@chromium.org>
> ---
> Changes since v1:
> - Added "Acked-by: Simon Glass".
>
> 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));
good catch. thanks.
>
> - timer_rate_hz = timer_rate_hz / CONFIG_SYS_HZ;
> + ticks_per_period = timer_rate_hz / pwm_hz;
why don't you use CONFIG_SYS_HZ?
pwm_hz seems to constant.
> + }
>
> /* 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))
>
Thanks,
Minkyu Kang.
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