Hi everyone,

I'm having a persistent and frustrating issue with brightness control on my ThinkPad X1 Yoga 2nd Gen. The problem is that the software seems to work, but the physical screen brightness doesn't change at all. I've tried all the common solutions and am looking for advice from anyone who might have experienced this on a similar machine.

System Details

• Model: ThinkPad X1 Yoga 2nd Gen (CPU: Intel HD Graphics 620
• OS: Fedora 42 with Hyprland (Wayland)
• Kernel: 6.15.10-200.fc42.x86_64
• BIOS: N1NET64W (1.51)
• Graphics Driver: i915

Problem Description

Brightness control is completely non-functional. The function keys (Fn+F5/F6) and software commands (like brightnessctl, echo > /sys/class/backlight/...) successfully change the system's brightness value (from 0 to 15), but there's no physical change in screen brightness.

What I've Tried (and what works)

• Software Methods:
  • brightnessctl s 50% - Changes the value but no physical effect.
  • echo 8 | sudo tee /sys/class/backlight/thinkpad_screen/brightness - Changes the value but no physical effect.
  • xbacklight - Reports "No outputs have backlight property".
• Kernel Parameters:
  • Tried various combinations like acpi_backlight=vendor, acpi_osi=Linux, i915.enable_dpcd_backlight=1. No combination has worked; some even remove the backlight interface entirely.
• Firmware Updates:
  • Updated the Embedded Controller (EC) from 0.1.16 to 0.1.19.
  • This FIXED my gamma/color temperature control (gammastep works now!), but did not fix brightness control.
  • fwupd reports no available BIOS updates.
• Other Tools:
  • wl-gammactl - Fails with "failed to set gamma table".
  • gammastep - Initially failed, but now works perfectly for color temperature adjustment since the EC update.

Current Status and Questions

It seems like there's a firmware-level lock preventing the Linux kernel from controlling the backlight, even though the EC update fixed gamma control.

1. Is this a known limitation of the ThinkPad X1 Yoga 2nd Gen with the Intel HD Graphics 620?
2. Are there any other kernel parameters I could try?
3. Has anyone with this exact model successfully fixed this?

Any suggestions or similar experiences would be greatly appreciated!