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;
--
2.9.4
