pwm: Add PWM polarity flag macro for DT

Define a PWM_POLARITY_INVERTED macro in include/dt-bindings/pwm/pwm.h to
be used by device tree sources.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/pwm.txt

@@ -43,13 +43,14 @@ because the name "backlight" would be used as fallback anyway.
 pwm-specifier typically encodes the chip-relative PWM number and the PWM
 period in nanoseconds.
 
-Optionally, the pwm-specifier can encode a number of flags in a third cell:
-- bit 0: PWM signal polarity (0: normal polarity, 1: inverse polarity)
+Optionally, the pwm-specifier can encode a number of flags (defined in
+<dt-bindings/pwm/pwm.h>) in a third cell:
+- PWM_POLARITY_INVERTED: invert the PWM signal polarity
 
 Example with optional PWM specifier for inverse polarity
 
 	bl: backlight {
-		pwms = <&pwm 0 5000000 1>;
+		pwms = <&pwm 0 5000000 PWM_POLARITY_INVERTED>;
 		pwm-names = "backlight";
 	};
 

include/dt-bindings/pwm/pwm.h

+/*
+ * This header provides constants for most PWM bindings.
+ *
+ * Most PWM bindings can include a flags cell as part of the PWM specifier.
+ * In most cases, the format of the flags cell uses the standard values
+ * defined in this header.
+ */
+
+#ifndef _DT_BINDINGS_PWM_PWM_H
+#define _DT_BINDINGS_PWM_PWM_H
+
+#define PWM_POLARITY_INVERTED			(1 << 0)
+
+#endif