From fb2081e870e9d59a0e6d076989e04c932c3ba23d Mon Sep 17 00:00:00 2001 From: Martin Blumenstingl Date: Wed, 12 Jun 2019 21:59:07 +0200 Subject: pwm: meson: Simplify the calculation of the pre-divider and count MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Replace the loop to calculate the pre-divider and count with two separate div64_u64() calculations. This makes the code easier to read and improves the precision. Three example cases: 1) 32.768kHz LPO clock for the SDIO wifi chip on Khadas VIM clock input: 500MHz (FCLK_DIV4) period: 30518ns duty cycle: 15259ns old algorithm: pre_div=0, cnt=15259 new algorithm: pre_div=0, cnt=15259 (no difference in calculated values) 2) PWM LED on Khadas VIM clock input: 24MHz (XTAL) period: 7812500ns duty cycle: 7812500ns old algorithm: pre_div=2, cnt=62004 new algorithm: pre_div=2, cnt=62500 Using a scope (24MHz sampling rate) shows the actual difference: - old: 7753000ns, off by -59500ns (0.7616%) - new: 7815000ns, off by +2500ns (0.032%) 3) Theoretical case where pre_div is different clock input: 24MHz (XTAL) period: 2730624ns duty cycle: 1365312ns old algorithm: pre_div=1, cnt=32768 new algorithm: pre_div=0, cnt=65534 Using a scope (24MHz sampling rate) shows the actual difference: - old: 2731000ns - new: 2731000ns (my scope is not precise enough to measure the difference if there's any) Suggested-by: Uwe Kleine-König Acked-by: Uwe Kleine-König Reviewed-by: Neil Armstrong Signed-off-by: Martin Blumenstingl Signed-off-by: Thierry Reding --- drivers/pwm/pwm-meson.c | 25 ++++++++++--------------- 1 file changed, 10 insertions(+), 15 deletions(-) diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c index 8a5658f2b947..99815b26f6b2 100644 --- a/drivers/pwm/pwm-meson.c +++ b/drivers/pwm/pwm-meson.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -145,7 +146,6 @@ static int meson_pwm_calc(struct meson_pwm *meson, struct pwm_device *pwm, struct meson_pwm_channel *channel = pwm_get_chip_data(pwm); unsigned int duty, period, pre_div, cnt, duty_cnt; unsigned long fin_freq = -1; - u64 fin_ps; duty = state->duty_cycle; period = state->period; @@ -164,24 +164,19 @@ static int meson_pwm_calc(struct meson_pwm *meson, struct pwm_device *pwm, } dev_dbg(meson->chip.dev, "fin_freq: %lu Hz\n", 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_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; - } + pre_div = div64_u64(fin_freq * (u64)period, NSEC_PER_SEC * 0xffffLL); if (pre_div > MISC_CLK_DIV_MASK) { dev_err(meson->chip.dev, "unable to get period pre_div\n"); return -EINVAL; } + cnt = div64_u64(fin_freq * (u64)period, NSEC_PER_SEC * (pre_div + 1)); + if (cnt > 0xffff) { + dev_err(meson->chip.dev, "unable to get period cnt\n"); + return -EINVAL; + } + dev_dbg(meson->chip.dev, "period=%u pre_div=%u cnt=%u\n", period, pre_div, cnt); @@ -195,8 +190,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, struct pwm_device *pwm, channel->lo = cnt; } else { /* Then check is we can have the duty with the same pre_div */ - duty_cnt = DIV_ROUND_CLOSEST_ULL((u64)duty * 1000, - fin_ps * (pre_div + 1)); + duty_cnt = div64_u64(fin_freq * (u64)duty, + NSEC_PER_SEC * (pre_div + 1)); if (duty_cnt > 0xffff) { dev_err(meson->chip.dev, "unable to get duty cycle\n"); return -EINVAL; -- cgit v1.2.3-59-g8ed1b