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authorJerome Brunet <jbrunet@baylibre.com>2017-06-08 14:24:16 +0200
committerThierry Reding <thierry.reding@gmail.com>2017-07-06 17:15:43 +0200
commitfd7b2be8cbcf6cd6d9c9e843ffff36fb91388e51 (patch)
tree38cb89e55f2c019beae1b503392f788eddf164ff /drivers/pwm
parentd396b20a1e88ca2cabf7ec99c6c2138902aff1f3 (diff)
pwm: meson: Improve PWM calculation precision
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 introduces an error of ~20% on the period requested from the PWM. This patch uses ps instead of ns (and 64 bit integers) 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 <jbrunet@baylibre.com> Acked-by: Neil Armstrong <narmstrong@baylibre.com> Signed-off-by: Thierry Reding <thierry.reding@gmail.com> squash! pwm: meson: Improve pwm calculation precision
Diffstat (limited to 'drivers/pwm')
-rw-r--r--drivers/pwm/pwm-meson.c16
1 files changed, 10 insertions, 6 deletions
diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index defc27d880f3..cb845edfe2b4 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 +180,15 @@ 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;
+ do_div(fin_ps, 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 +211,8 @@ 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;