pwm: sunxi: fix off-by-one that prevented PWM to use prescaler bypass

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 <[email protected]>

---
 drivers/pwm/sunxi_pwm.c | 32 +++++++++++++++++++-------------
 1 file changed, 19 insertions(+), 13 deletions(-)

drivers/pwm/sunxi_pwm.c +17 -12

index 6284409b4f..8a55e4f461 100644
@@ -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) |

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.

Quoted 4 lines · Vasily Khoruzhick

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.

This commit need to elaborate about the real issue, ie got fixed. Understand it has chosen best prescaler but why and how it.

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 <[email protected]>

---

Quoted 7 lines · Vasily Khoruzhick

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 <[email protected]>

---

Applied to all to u-boot-sunxi/master

Fix off-by-one that prevented PWM driver to use prescaler bypass. Without this change prescaler is always enabled.

Signed-off-by Vasily Khoruzhick <[email protected]>

Fix off-by-one that prevented PWM driver to use prescaler bypass. Without this change prescaler is always enabled.

Signed-off-by Vasily Khoruzhick <[email protected]>

---
 drivers/pwm/sunxi_pwm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)