[linux-sunxi] pwm: sun4i: pwm-backlight not working since 5.6-rc1

[Pascal Roeleven]

Hi all,

I am working on adding an old A10 device to mainline and noticed an 
issue when testing on 5.5.8 vs master.

Since 5.6-rc1, I can't control the brightness of my LCD backlight 
anymore. The backlight stays on full brightness instead. I am 
controlling the brightness value via sysfs for testing.

I am not sure if this is a general pwm-sun4i issue or if it is related 
to the backlight. However I narrowed it down to one commit for 
pwm-sun4i:

fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5

If I use pwm-sun4i.c from 5b090b430d750961305030232314b6acdb0102aa on 
master, the backlight works fine. Unfortunately, due to my lack of 
kernel experience, I can't see how the commit above broke it.

Not sure if it helps, but the binding for the backlight is as follows:

backlight: backlight {
    compatible = "pwm-backlight";
    pwms = <&pwm 0 100000 PWM_POLARITY_INVERTED>;
    power-supply = <&reg_vbat>;
    enable-gpios = <&pio 7 7 GPIO_ACTIVE_HIGH>; /* PH7 */
    brightness-levels = <0 30 40 50 60 70 80 90 100>;
    default-brightness-level = <8>;
};

Please let me know if there is anything else which might be helpful to 
know or anything I can test.

Regards,
Pascal

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