Created attachment 4476 [details]
patch file

The udev code labels devices that are found by this code with
ID_INPUT_KEY which in turn gets used by SDL to label the devices as
SDL_UDEV_DEVICE_KEYBOARD.
    
This was missing for the code path when udev is not running and as such
devices such as the power button of a phone was not detected as keyboard
input and no devices were emitted.

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I've also noticed that the commit/revision(?) https://hg.libsdl.org/SDL/rev/2b2cfda26085 tries to do that somewhat but it only looks at the first 32 bits instead of also at the rest of the bits. This results in the behavior that e.g. the power button driver axp20x-pek of the Allwinner A64 platform doesn't get labelled as keyboard which results in no events being emitted to applications using sdl.

Supported events:
  Event type 0 (EV_SYN)
  Event type 1 (EV_KEY)
    Event code 116 (KEY_POWER)

In the normal code path where udev properties get used this works because udev correctly labels the device as ID_INPUT_KEY which sdl then uses for SDL_UDEV_DEVICE_KEYBOARD, but it didn't work for the fallback codepath for when udev isn't running (e.g. in initramfs where only busybox mdev is used)

**Also note** that the code is pretty much copied from systemd/udev code, I'm not sure about the licensing side of things - but also I don't think the code can be written much different but please know that.