ARM: dts: ixp4xx: nslu2: beeper uses PWM

The beeper in the NSLU2 is just a GPIO connected to a
speaker, so we need to use PWM on the GPIO to get any kind
of sound out.

Tested with some random beeps by enabling INPUT_EVDEV and
running beep.c with e.g. beep 400 for a 400 Hz tone.

Signed-off-by: Linus Walleij <[email protected]>
Link: https://lore.kernel.org/[email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnd Bergmann <[email protected]>

Author: linusw

arch/arm/boot/dts/intel/ixp/intel-ixp42x-linksys-nslu2.dts

@@ -90,11 +90,18 @@
 		timeout-ms = <5000>;
 	};
 
-	gpio-beeper {
-		compatible = "gpio-beeper";
+	gpio_pwm: pwm {
+		#pwm-cells = <3>;
+		compatible = "pwm-gpio";
 		gpios = <&gpio0 4 GPIO_ACTIVE_HIGH>;
 	};
 
+	beeper {
+		compatible = "pwm-beeper";
+		pwms = <&gpio_pwm 0 1 0>;
+		beeper-hz = <1000>;
+	};
+
 	soc {
 		bus@c4000000 {
 			/* The first 16MB region at CS0 on the expansion bus */