On 06/08/2017 02:24 PM, Jerome Brunet wrote:
> When using input clocks with high rates, such as clk81 (166MHz), the
> fin_ns = NSEC_PER_SEC / fin_freq can introduce a significant error.
>
> Ex: fin_freq = 166666667, NSEC_PER_SEC = 1000000000
> fin_ns = 5,9999999
>
> which is, of course, rounded down to 5. This introduce an error of ~20%
> on the period requested from the pwm.
>
> This patch use ps instead of ns (and 64bits integer) to perform the
> calculation. This should give a good enough precision.
>
> Fixes: 211ed630753d ("pwm: Add support for Meson PWM Controller")
> Signed-off-by: Jerome Brunet <[email protected]>
> ---
> drivers/pwm/pwm-meson.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
> index b911a944744a..4cdc66f7f718 100644
> --- a/drivers/pwm/pwm-meson.c
> +++ b/drivers/pwm/pwm-meson.c
> @@ -163,7 +163,8 @@ static int meson_pwm_calc(struct meson_pwm *meson,
> unsigned int duty, unsigned int period)
> {
> unsigned int pre_div, cnt, duty_cnt;
> - unsigned long fin_freq = -1, fin_ns;
> + unsigned long fin_freq = -1;
> + u64 fin_ps;
>
> if (~(meson->inverter_mask >> id) & 0x1)
> duty = period - duty;
> @@ -179,13 +180,14 @@ static int meson_pwm_calc(struct meson_pwm *meson,
> }
>
> dev_dbg(meson->chip.dev, "fin_freq: %lu Hz\n", fin_freq);
> - fin_ns = NSEC_PER_SEC / fin_freq;
> + fin_ps = ((u64)NSEC_PER_SEC * 1000) / fin_freq;
>
> /* Calc pre_div with the period */
> for (pre_div = 0; pre_div < MISC_CLK_DIV_MASK; pre_div++) {
> - cnt = DIV_ROUND_CLOSEST(period, fin_ns * (pre_div + 1));
> - dev_dbg(meson->chip.dev, "fin_ns=%lu pre_div=%u cnt=%u\n",
> - fin_ns, pre_div, cnt);
> + cnt = DIV_ROUND_CLOSEST_ULL((u64)period * 1000,
> + fin_ps * (pre_div + 1));
> + dev_dbg(meson->chip.dev, "fin_ps=%llu pre_div=%u cnt=%u\n",
> + fin_ps, pre_div, cnt);
> if (cnt <= 0xffff)
> break;
> }
> @@ -208,7 +210,8 @@ static int meson_pwm_calc(struct meson_pwm *meson,
> channel->lo = cnt;
> } else {
> /* Then check is we can have the duty with the same pre_div */
> - duty_cnt = DIV_ROUND_CLOSEST(duty, fin_ns * (pre_div + 1));
> + duty_cnt = DIV_ROUND_CLOSEST_ULL((u64)duty * 1000,
> + fin_ps * (pre_div + 1));
> if (duty_cnt > 0xffff) {
> dev_err(meson->chip.dev, "unable to get duty cycle\n");
> return -EINVAL;
>
Great, I missed this !!
Acked-by: Neil Armstrong <[email protected]>
