pwm: lpc32xx: Properly set PWM_ENABLE bit in lpc32xx_pwm_[enable|disable]

According to the LPC32x0 User Manual [1]:

For both PWM1 and PWM2 Control Registers:
BIT 31:
This bit gates the PWM_CLK signal and enables the external output pin
to the PWM_PIN_STATE logical level.

0 = PWM disabled. (Default)
1 = PWM enabled

So in lpc32xx_pwm_enable(), we should set PWM_ENABLE bit.
In lpc32xx_pwm_disable(), we should just clear PWM_ENABLE bit rather than
write 0 to the register which will also clear PWMx_RELOADV and PWMx_DUTY bits.

[1] http://www.nxp.com/documents/user_manual/UM10326.pdf

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Roland Stigge <stigge@antcom.de>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>

drivers/pwm/pwm-lpc32xx.c

@@ -77,15 +77,29 @@ static int lpc32xx_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 static int lpc32xx_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
 {
 	struct lpc32xx_pwm_chip *lpc32xx = to_lpc32xx_pwm_chip(chip);
+	u32 val;
+	int ret;
+
+	ret = clk_enable(lpc32xx->clk);
+	if (ret)
+		return ret;
 
-	return clk_enable(lpc32xx->clk);
+	val = readl(lpc32xx->base + (pwm->hwpwm << 2));
+	val |= PWM_ENABLE;
+	writel(val, lpc32xx->base + (pwm->hwpwm << 2));
+
+	return 0;
 }
 
 static void lpc32xx_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
 {
 	struct lpc32xx_pwm_chip *lpc32xx = to_lpc32xx_pwm_chip(chip);
+	u32 val;
+
+	val = readl(lpc32xx->base + (pwm->hwpwm << 2));
+	val &= ~PWM_ENABLE;
+	writel(val, lpc32xx->base + (pwm->hwpwm << 2));
 
-	writel(0, lpc32xx->base + (pwm->hwpwm << 2));
 	clk_disable(lpc32xx->clk);
 }