Add PWM support for Raspberry Pi 5 (RP1/PIO)

[awawa-dev]

Add support for GPIO PWM for Raspberry Pi 5 using its RP1/PIO controller.
1 Requires root! Works only for Raspberry Pi 5 or newer if equipped with RP1 controller.
2 Must define LED strip in the overlay first!

• For example: echo "dtoverlay=ws2812-pio,gpio=18,num_leds=30,rgbw" | sudo tee -a /boot/firmware/config.txt
  or edit /boot/firmware/config.txt manually
• Adjust num_leds: total number of LEDs, must be configured the same in HyperHDR
• Adjust rgbw only for sk6812 RGBW, otherwise remove it
• After editing /boot/firmware/config.txt restart is required
• If you configure everything correctly, you should see the /dev/leds0 device

Warning

Requires fixed ws2812 PIO kernel module: raspberrypi/linux#7108
As for 2025-10-29 you need to switch Trixie kernel to testing kernel version and reboot:
sudo rpi-update beb2783757e6aa6c4abe4187dc74da4ce2f451fc
It will be included in the next RPi OS release for kernel > 6.12.55

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Testing setup:

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Results of testing using fixed kernel module:

Kernel driver hardcoded gamma causing its useless:
input 1–6 → 0,
input 7–8 → 1,
…
input 128 → 55 (0x37),
input 224 → 191 (0xBF),
input 255 → 255.

so it makes from LED strip capable of rendering 256x256x256 colors something inferior that is capable of rendering around 120x120x120 even if we would reverse that unfortunate gamma on our side (set: user gamma to 0.4545 in the processing tab) due to the gamma compression