pwm: optimizing pwm duty calculation

PD#165143: pwm: optimizing pwm duty calculation

1.Fix duty equal 0% and 100% duty count incorrect
2.Change period unit to ps to increase accuracy

Change-Id: Ied478f21ac4b4f9f3d1508d69dfbcdbb9ca4e732
Signed-off-by: Jian Hu <jian.hu@amlogic.com>

diff --git a/drivers/amlogic/pwm/pwm_meson.c b/drivers/amlogic/pwm/pwm_meson.c
index af658ac..e7b1b1d 100644 (file)
--- a/drivers/amlogic/pwm/pwm_meson.c
+++ b/drivers/amlogic/pwm/pwm_meson.c
@@ -164,7 +164,8 @@ 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;
@@ -180,13 +181,15 @@ 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_ns=%llu pre_div=%u cnt=%u\n",
+                       fin_ps, pre_div, cnt);
                if (cnt <= 0xffff)
                        break;
        }
@@ -201,15 +204,16 @@ static int meson_pwm_calc(struct meson_pwm *meson,
 
        if (duty == period) {
                channel->pre_div = pre_div;
-               channel->hi = cnt;
+               channel->hi = cnt - 1;
                channel->lo = 0;
        } else if (duty == 0) {
                channel->pre_div = pre_div;
                channel->hi = 0;
-               channel->lo = cnt;
+               channel->lo = cnt - 1;
        } 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;