diff options
| author | Jerome Brunet <jbrunet@baylibre.com> | 2017-06-08 14:24:16 +0200 |
|---|---|---|
| committer | Thierry Reding <thierry.reding@gmail.com> | 2017-07-06 17:15:43 +0200 |
| commit | fd7b2be8cbcf6cd6d9c9e843ffff36fb91388e51 (patch) | |
| tree | 38cb89e55f2c019beae1b503392f788eddf164ff /drivers/pwm | |
| parent | d396b20a1e88ca2cabf7ec99c6c2138902aff1f3 (diff) | |
| download | linux-fd7b2be8cbcf6cd6d9c9e843ffff36fb91388e51.tar.bz2 | |
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.c | 16 |
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; |