pwm: vt8500: Ensure PWM clock is enabled during pwm_config

This patch corrects a bug reported by Peter Vasil.

When all PWMs are disabled, PWM module may be disabled during
calls to pwm_config. This patch enables/disables the clock in
pwm_config to ensure the module is active before register read/
writes.
Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Tested-by: Peter Vasil <petervasil@gmail.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>

drivers/pwm/pwm-vt8500.c

@@ -62,6 +62,13 @@ static int vt8500_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	struct vt8500_chip *vt8500 = to_vt8500_chip(chip);
 	unsigned long long c;
 	unsigned long period_cycles, prescale, pv, dc;
+	int err;
+
+	err = clk_enable(vt8500->clk);
+	if (err < 0) {
+		dev_err(chip->dev, "failed to enable clock\n");
+		return err;
+	}
 
 	c = clk_get_rate(vt8500->clk);
 	c = c * period_ns;
@@ -75,8 +82,10 @@ static int vt8500_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	if (pv > 4095)
 		pv = 4095;
 
-	if (prescale > 1023)
+	if (prescale > 1023) {
+		clk_disable(vt8500->clk);
 		return -EINVAL;
+	}
 
 	c = (unsigned long long)pv * duty_ns;
 	do_div(c, period_ns);
@@ -91,6 +100,7 @@ static int vt8500_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	pwm_busy_wait(vt8500->base + 0x40 + pwm->hwpwm, (1 << 3));
 	writel(dc, vt8500->base + 0xc + (pwm->hwpwm << 4));
 
+	clk_disable(vt8500->clk);
 	return 0;
 }
 
@@ -103,7 +113,7 @@ static int vt8500_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
 	if (err < 0) {
 		dev_err(chip->dev, "failed to enable clock\n");
 		return err;
-	};
+	}
 
 	pwm_busy_wait(vt8500->base + 0x40 + pwm->hwpwm, (1 << 0));
 	writel(5, vt8500->base + (pwm->hwpwm << 4));