Choose best prescaler to improve PWM resolution. Without this change driver chooses first prescaler that gives us period value within range, but it could be not the best one.
Signed-off-by: Vasily Khoruzhick anarsoul@gmail.com --- drivers/pwm/sunxi_pwm.c | 32 +++++++++++++++++++------------- 1 file changed, 19 insertions(+), 13 deletions(-)
diff --git a/drivers/pwm/sunxi_pwm.c b/drivers/pwm/sunxi_pwm.c index 6284409b4f..8a55e4f461 100644 --- a/drivers/pwm/sunxi_pwm.c +++ b/drivers/pwm/sunxi_pwm.c @@ -67,49 +67,55 @@ static int sunxi_pwm_set_config(struct udevice *dev, uint channel, { struct sunxi_pwm_priv *priv = dev_get_priv(dev); struct sunxi_pwm *regs = priv->regs; - int prescaler; - u32 v, period = 0, duty; - u64 scaled_freq = 0; + int best_prescaler = 0; + u32 v, best_period = 0, duty; + u64 best_scaled_freq = 0; const u32 nsecs_per_sec = 1000000000U;
debug("%s: period_ns=%u, duty_ns=%u\n", __func__, period_ns, duty_ns);
- for (prescaler = 0; prescaler <= SUNXI_PWM_CTRL_PRESCALE0_MASK; + for (int prescaler = 0; prescaler <= SUNXI_PWM_CTRL_PRESCALE0_MASK; prescaler++) { + u32 period = 0; + u64 scaled_freq = 0; if (!prescaler_table[prescaler]) continue; scaled_freq = lldiv(OSC_24MHZ, prescaler_table[prescaler]); period = lldiv(scaled_freq * period_ns, nsecs_per_sec); - if (period - 1 <= SUNXI_PWM_CH0_PERIOD_MAX) - break; + if ((period - 1 <= SUNXI_PWM_CH0_PERIOD_MAX) && + best_period < period) { + best_period = period; + best_scaled_freq = scaled_freq; + best_prescaler = prescaler; + } }
- if (period - 1 > SUNXI_PWM_CH0_PERIOD_MAX) { + if (best_period - 1 > SUNXI_PWM_CH0_PERIOD_MAX) { debug("%s: failed to find prescaler value\n", __func__); return -EINVAL; }
- duty = lldiv(scaled_freq * duty_ns, nsecs_per_sec); + duty = lldiv(best_scaled_freq * duty_ns, nsecs_per_sec);
- if (priv->prescaler != prescaler) { + if (priv->prescaler != best_prescaler) { /* Mask clock to update prescaler */ v = readl(®s->ctrl); v &= ~SUNXI_PWM_CTRL_CLK_GATE; writel(v, ®s->ctrl); v &= ~SUNXI_PWM_CTRL_PRESCALE0_MASK; - v |= (prescaler & SUNXI_PWM_CTRL_PRESCALE0_MASK); + v |= (best_prescaler & SUNXI_PWM_CTRL_PRESCALE0_MASK); writel(v, ®s->ctrl); v |= SUNXI_PWM_CTRL_CLK_GATE; writel(v, ®s->ctrl); - priv->prescaler = prescaler; + priv->prescaler = best_prescaler; }
- writel(SUNXI_PWM_CH0_PERIOD_PRD(period) | + writel(SUNXI_PWM_CH0_PERIOD_PRD(best_period) | SUNXI_PWM_CH0_PERIOD_DUTY(duty), ®s->ch0_period);
debug("%s: prescaler: %d, period: %d, duty: %d\n", __func__, priv->prescaler, - period, duty); + best_period, duty);
return 0; }