https://bugzilla.kernel.org/show_bug.cgi?id=221110
Bug ID: 221110
Summary: amdgpu DM skips backlight registration on ASUS TUF A14
(DCN 3.5) due to ATPX detection regardless of active
GPU mode
Product: Drivers
Version: 2.5
Hardware: AMD
OS: Linux
Status: NEW
Severity: normal
Priority: P3
Component: Video(DRI - non Intel)
Assignee: [email protected]
Reporter: [email protected]
Regression: No
Hardware:
Laptop: ASUS TUF A14
Panel: BOE NE140QDM-NX7
iGPU: AMD (DCN 3.5)
dGPU: NVIDIA (disabled via vga_switcheroo / supergfxctl, Integrated mode
active)
Kernel: 6.17.9-76061709-generic
Problem:
No backlight device is registered in /sys/class/backlight/ when booting in
Integrated GPU mode. Brightness control is completely non-functional.
Kernel log showing root cause:
[3.831962] amdgpu: vga_switcheroo: detected switching method
\_SB_.PCI0.GPPA.VGA_.ATPX handle
[3.832035] amdgpu: ATPX version 1, functions 0x00000801
[3.832077] amdgpu: ATPX Hybrid Graphics
[4.320982] amdgpu 0000:65:00.0: amdgpu: [drm] Skipping amdgpu DM backlight
registration
The amdgpu driver detects ATPX at 3.83s and skips backlight registration at
4.32s. The skip occurs unconditionally based on ATPX presence, without checking
whether vga_switcheroo has actually handed display control to the iGPU. When in
Integrated mode, amdgpu owns the display pipeline (DCN 3.5 active, eDP-1
connected to card0) but does not register a backlight device.
Confirmed not caused by:
asus_wmi / asus-nb-wmi (loads at 6.08s, after the skip at 4.32s)
Missing ACPI backlight method (DSDT contains no backlight method)
Panel quirk (BOE NE140QDM-NX7 has no known quirk entry)
Kernel parameters tested with no effect:
amdgpu.backlight=0 / amdgpu.backlight=1
acpi_backlight=native
acpi_backlight=video
acpi_backlight=vendor
ATPX functions value: 0x00000801
Expected behavior:
When vga_switcheroo/supergfxctl has placed the system in Integrated mode and
the AMD iGPU owns the display pipeline, amdgpu DM should register a backlight
device normally regardless of ATPX presence.
Additional info:
/proc/acpi/video/ does not exist
card0-eDP-1 is the active internal panel path
NVIDIA modules are fully unloaded in Integrated mode
supergfxctl -g confirms Integrated
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