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pwm: sunxi: choose best prescaler to improve PWM resolution

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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>
Tested-by: Vagrant Cascadian <vagrant@debian.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
This commit is contained in:
Vasily Khoruzhick 2018-10-16 21:56:35 -07:00 committed by Jagan Teki
parent ce138cb429
commit c33ba7ec8b
1 changed files with 19 additions and 13 deletions
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32
drivers/pwm/sunxi_pwm.c
View file

@ -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(&regs->ctrl);
v &= ~SUNXI_PWM_CTRL_CLK_GATE;
writel(v, &regs->ctrl);
v &= ~SUNXI_PWM_CTRL_PRESCALE0_MASK;
v |= (prescaler & SUNXI_PWM_CTRL_PRESCALE0_MASK);
v |= (best_prescaler & SUNXI_PWM_CTRL_PRESCALE0_MASK);
writel(v, &regs->ctrl);
v |= SUNXI_PWM_CTRL_CLK_GATE;
writel(v, &regs->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), &regs->ch0_period);
debug("%s: prescaler: %d, period: %d, duty: %d\n",
__func__, priv->prescaler,
period, duty);
best_period, duty);
return 0;
}