pwm: vt8500: Add polarity support

Add support to set polarity on PWM devices, allowing for inverted
duty cycles.

Also update the binding document to #pwm-cells = <3> to allow
passing the flags from devicetree.

Signed-off-by: Tony Prisk <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

Documentation/devicetree/bindings/pwm/vt8500-pwm.txt

···
 Required properties:
 - compatible: should be "via,vt8500-pwm"
 - reg: physical base address and length of the controller's registers
-- #pwm-cells: should be 2.  The first cell specifies the per-chip index
-  of the PWM to use and the second cell is the period in nanoseconds.
+- #pwm-cells: Should be 3. Number of cells being used to specify PWM property.
+  First cell specifies the per-chip index of the PWM to use, the second
+  cell is the period in nanoseconds and bit 0 in the third cell is used to
+  encode the polarity of PWM output. Set bit 0 of the third in PWM specifier
+  to 1 for inverse polarity & set to 0 for normal polarity.
 - clocks: phandle to the PWM source clock
 
 Example:
 
 pwm1: pwm@d8220000 {
-	#pwm-cells = <2>;
+	#pwm-cells = <3>;
 	compatible = "via,vt8500-pwm";
 	reg = <0xd8220000 0x1000>;
 	clocks = <&clkpwm>;

drivers/pwm/pwm-vt8500.c

···
 	clk_disable(vt8500->clk);
 }
 
+static int vt8500_pwm_set_polarity(struct pwm_chip *chip,
+				   struct pwm_device *pwm,
+				   enum pwm_polarity polarity)
+{
+	struct vt8500_chip *vt8500 = to_vt8500_chip(chip);
+	u32 val;
+
+	val = readl(vt8500->base + REG_CTRL(pwm->hwpwm));
+
+	if (polarity == PWM_POLARITY_INVERSED)
+		val |= CTRL_INVERT;
+	else
+		val &= ~CTRL_INVERT;
+
+	writel(val, vt8500->base + REG_CTRL(pwm->hwpwm));
+	pwm_busy_wait(vt8500, pwm->hwpwm, STATUS_CTRL_UPDATE);
+
+	return 0;
+}
+
 static struct pwm_ops vt8500_pwm_ops = {
 	.enable = vt8500_pwm_enable,
 	.disable = vt8500_pwm_disable,
 	.config = vt8500_pwm_config,
+	.set_polarity = vt8500_pwm_set_polarity,
 	.owner = THIS_MODULE,
 };
 
···
 
 	chip->chip.dev = &pdev->dev;
 	chip->chip.ops = &vt8500_pwm_ops;
+	chip->chip.of_xlate = of_pwm_xlate_with_flags;
+	chip->chip.of_pwm_n_cells = 3;
 	chip->chip.base = -1;
 	chip->chip.npwm = VT8500_NR_PWMS;