Thanks for getting these drivers submitted upstream!

I don't really know anything about PWM, so just some random nitpicking
below..

+	iowrite32(frac, pwm->regs + REG_PWMCMP0 + (dev->hwpwm * SIZE_PWMCMP));

* already has a higher precedence than +, so no need for the inner
braces.

+	duty = ioread32(pwm->regs + REG_PWMCMP0 + (dev->hwpwm * SIZE_PWMCMP));

Same here.

+	/* (1 << (16+scale)) * 10^9/rate = real_period */

	unsigned long scalePow = (pwm->approx_period * (u64)rate) / 1000000000;

no camcel case, please.

+	int scale = ilog2(scalePow) - 16;
+
+	scale = clamp(scale, 0, 0xf);

Why not:

	int scale = clamp(ilog2(scale_pow) - 16, 0, 0xf);

+static int sifive_pwm_clock_notifier(struct notifier_block *nb,
+				     unsigned long event, void *data)
+{
+	struct clk_notifier_data *ndata = data;
+	struct sifive_pwm_device *pwm = container_of(nb,
+						     struct sifive_pwm_device,
+						     notifier);

I don't think there are any guidlines, but I always prefer to just move
the whole container_of onto a new line:

	struct sifive_pwm_device *pwm =
		container_of(nb, struct sifive_pwm_device, notifier);

+static struct platform_driver sifive_pwm_driver = {
+	.probe = sifive_pwm_probe,
+	.remove = sifive_pwm_remove,
+	.driver = {
+		.name = "pwm-sifivem",
+		.of_match_table = of_match_ptr(sifive_pwm_of_match),
+	},
+};

What about using tabs to align this a little more nicely?

static struct platform_driver sifive_pwm_driver = {
	.probe			= sifive_pwm_probe,
	.remove			= sifive_pwm_remove,
	.driver = {
		.name		= "pwm-sifivem",
		.of_match_table	= of_match_ptr(sifive_pwm_of_match),
	},
};