https://bugzilla.kernel.org/show_bug.cgi?id=220487
Bug ID: 220487
Summary: ThinkPad X1 Yoga 2nd Gen: Brightness control
non-functional with i915 (ACPI)
Product: ACPI
Version: 2.5
Hardware: Intel
OS: Linux
Status: NEW
Severity: normal
Priority: P3
Component: Power-Video
Assignee: [email protected]
Reporter: [email protected]
Regression: No
ThinkPad X1 Yoga 2nd Gen - Brightness Control Not Working on Linux
System Information
Model: ThinkPad X1 Yoga 2nd Gen
CPU: Intel HD Graphics 620
OS: Fedora 42 with Hyprland (Wayland) ML4W dotfiles
Kernel: 6.15.10-200.fc42.x86_64
BIOS: N1NET64W (1.51)
Graphics Driver: i915
Problem Description
Brightness control completely non-functional - software changes values but
screen brightness doesn't change physically
Gamma/color temperature control was initially broken but is now working after
EC update
Function keys (Fn+F5/F6) also don't change physical brightness despite changing
system values
Hardware Detection
# Graphics card detected properly:
lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation HD Graphics 620 (rev 02)
# i915 driver loaded:
lsmod | grep i915
i915 5283840 34
# Monitor detected:
hyprctl monitors
Monitor eDP-1 (ID 0): [email protected]
description: Lenovo Group Limited 0x4140
# Backlight interfaces exist:
ls /sys/class/backlight/
thinkpad_screen -> ../../devices/virtual/backlight/thinkpad_screen
# ThinkPad ACPI available:
ls /proc/acpi/ibm/
brightness # exists but non-functional
What Was Tested
Software Methods (All Failed)
brightnessctl s 50% - changes value (0-15) but no physical effect
echo 8 | sudo tee /sys/class/backlight/thinkpad_screen/brightness - changes
value but no physical effect
echo "level 10" | sudo tee /proc/acpi/ibm/brightness - changes value but no
physical effect
light -S 50 - no effect
xbacklight -set 50 - "No outputs have backlight property"
Gamma Control Tools
BEFORE EC update: gammastep -O 4000 showed "Warning: Zero outputs support gamma
adjustment"
AFTER EC update: gammastep -O 4000 WORKS PERFECTLY ✅
Kernel Parameters Tested
Original: acpi_backlight=vendor acpi_osi=Linux
Attempted fix: acpi_osi=! acpi_osi="Windows 2012" acpi_backlight=none
i915.enable_dpcd_backlight=1This completely removed all backlight interfaces
Reverted to: acpi_backlight=vendor acpi_osi=Linux (current)
Hardware Tests
Function keys (Fn+F5/F6): Change system brightness values but no physical
effect
DDC/CI: ddcutil detect reports "This is a laptop display. Laptop displays do
not support DDC/CI"
External monitors: Not tested
Firmware Updates
Intel Management Engine: 182.29.3287 → 184.96.4657 ✅
Embedded Controller: 0.1.16 → 0.1.19 ✅
System Firmware/BIOS: No updates available via fwupd
Current Status
Gamma control: ✅ WORKING (fixed after EC update)
Brightness control: ❌ NOT WORKING (firmware-locked)
Values change in software: ✅ Yes (0-15 range)
Physical brightness change: ❌ No
Technical Details
# Current brightness interface values:
cat /sys/class/backlight/thinkpad_screen/max_brightness # 15
cat /sys/class/backlight/thinkpad_screen/brightness # Changes but no effect
# ACPI brightness interface:
cat /proc/acpi/ibm/brightness
# level: 0 (or other values)
# commands: up, down, level <level> (0-15)
# Graphics driver parameters:
ls /sys/module/i915/parameters/
# enable_dpcd_backlight exists but shows "No access"
Questions for Community/Support
Is this a known hardware limitation of ThinkPad X1 Yoga 2nd Gen with Intel HD
Graphics 620?
Are there other kernel parameters specific to this model that might unlock
brightness control?
Could a BIOS update fix this issue? (Currently on 1.51, fwupd shows no BIOS
updates available)
Any low-level hardware tools that might bypass the firmware lock?
Has anyone successfully fixed brightness control on this exact model?
Workarounds Currently Using
Dark themes system-wide
Gamma control with gammastep for blue light filtering
Browser-based dimming when needed
Any suggestions or similar experiences would be greatly appreciated!
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