Empty /sys/class/backlight

[Detlef Vollmann <dv@vollmann.ch>]

Hello,

on my laptop (Lenovo X250) I run Debian testing.
On a recent upgrade the kernel was updated from 6.12.38+deb13-rt-amd64
to 6.16.3+deb14-rt-amd64 (and now to 6.16.9+deb14-rt-amd64).

With kernel 6.16 I lost /sys/class/backlight/intel_backlight.
I also don't have the i915 module anymore, which I suspect might
be related.
On booting 6.16 I still get the following line:
thinkpad_acpi: This ThinkPad has standard ACPI backlight brightness 
control, supported by the ACPI video driver

But I don't get any entry in /sys/class/backlight.

While searching on the internet I found that ACPI backlight
has changed with kernel 6.1, but 6.12 worked still fine.

Anybody has any clue what's the problem?

  Detlef