Re: [U-Boot] [U-Boot, 3/3] pwm: sunxi: choose best prescaler to improve PWM resolution

On 2018-10-16, Vasily Khoruzhick wrote:

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

Fixes LCD backlight issues with the pinebook series:

https://patchwork.ozlabs.org/project/uboot/list/?series=71358

Tested-by: Vagrant Cascadian vagrant@debian.org

---

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(&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;

}