buster drivers do not support brightness control

[sesquipedality]

Describe the bug

What's gone wrong?

The buster hyperpixel 4 driver exposes brightness control via
/sys/class/backlight/backlight/brightness. However this is a binary value, with 1 being full brightness and 0 being off. For apps that provide brightness control (e.g. using the Python screen_brightness_control library), this produces surprising and unhelpful behaviour where dropping the brightness below 100% turns off the screen.

To Reproduce

What install steps did you go through so far? Did you install from GitHub or use our one-line-installer?

Installed on a Hyperpixel 4 Square 2021 model on Pi OS 2022.9 using the add dtoverlay to config.txt method.

Can replicated this behaviour by echoing 1 or 0 to /sys/class/backlight/backlight/brightness. /sys/class/backlight/backlight/max-brightness confirms that only 0 and 1 are valid values for brightness

Your HyperPixel 4

Let us know which HyperPixel 4 board you're using. Note: if you're having a problem with the original HyperPixel you should go to: https://github.com/pimoroni/hyperpixel

1. Is it Square or Rectangular?
   Square
2. Touch or non Touch?
   Touch
3. Approximately when was it purchased
   Mid 2022
4. How is it connected to your Pi
   GPIO pins

Your Raspberry Pi

Give as much detail about your Pi and OS as possible. We only officially support Raspbian, but might be able to point you in the right direction if the problem is with another OS.

1. What model of Raspberry Pi are you using (the result of cat /proc/cpuinfo | grep Revision can tell us this exactly

Pi 3B
Revision : a020d3

3. Which OS release are you using: lsb_release --description and uname -r

Description: Debian GNU/Linux 11 (bullseye)
5.15.61-v8+

5. Is this a fresh OS setup, or one you might have previously installed scripts/add-ons on?

Fresh setup

Extra debugging information
I understand that there have been some previous attempts to implement brightness control in driver using PWM.