Wrap PWM output as GPIO

[6by9]

This needs a dt binding, but I wondered what people thought.

Scenario is for things like DSI screens where we have I2C up the FFC, and want a combination of GPIO outputs for resets and regulators, and PWM for the backlight.
You can get chips such as NXP PCA9685 which gives 16 PWM outputs, or you can get I2C expanders that give GPIOs. To avoid having to put both on the controller board, wrap some PWM outputs of an PCA9685 as GPIO outputs, and drive them as such.

https://forums.raspberrypi.com/viewtopic.php?f=98&t=321245&p=1925007

One thing that would be nice to do would be to read an array of PWM outputs and create a single gpiochip supporting all of them. Currently you need a separate instance for each output. I couldn't see a way of configuring multiple PWM devices without also specifying names for each one, but I may have just missed it.

[6by9]

Updated to wrap all PWMs listed in DT as GPIOs. Names are needed due to the way the way the API works.

dtoverlay hack dropped as it doesn't want to be merged. For reference, it was

+
+       fragment@1 {
+               target-path = "/";
+               __overlay__ {
+                       pwm_gpio: pwm_gpio@0 {
+                               compatible = "pwm-gpio";
+                               reg = <0x0>;
+                               gpio-controller;
+                               #gpio-cells = <2>;
+
+                               pwms =  <&pca 15 1000000>, //100ns or 1kHz
+                                       <&pca 14 1000000>,
+                                       <&pca 13 1000000>;
+                               pwm-names = "gpio1", "gpio2", "gpio3";
+
+                               status = "okay";
+                       };
+               };
+       };
+

Copying the example set by gpio-fsm, no dt binding doc as it won't be acceptable to upstream anyway ;-)

[pelwell]

I'm happy with that. Any objections to me ignoring the "RFC" and merging?

[6by9]

RFC removed