Messages in this thread | | | Date | Thu, 6 Jul 2017 23:21:57 +0200 | From | Thierry Reding <> | Subject | Re: [PATCH v2 3/3] pwm: meson: improve pwm calculation precision. |
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On Thu, Jun 08, 2017 at 02:24:16PM +0200, 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 <jbrunet@baylibre.com> > --- > 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;
This failed to build, so I had to change this division to a do_div().
Thierry [unhandled content-type:application/pgp-signature] | |