From c33ba7ec8b9be0a6fe7a2bd47a36c991bf9189e1 Mon Sep 17 00:00:00 2001 From: Vasily Khoruzhick Date: Tue, 16 Oct 2018 21:56:35 -0700 Subject: [PATCH] pwm: sunxi: choose best prescaler to improve PWM resolution 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 Tested-by: Vagrant Cascadian Acked-by: Maxime Ripard Reviewed-by: Jagan Teki --- 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; } -- 2.30.2