feat(predator): add PHN16-72 back logo/lightbar support

[0PeterAdel]

Summary

Adds hardware-backed RGB control for the rear Predator logo/lightbar on Acer Predator PHN16-72 systems.

The feature is model-gated through ACER_CAP_BACK_LOGO and exposes:

/sys/module/linuwu_sense/drivers/platform:acer-wmi/acer-wmi/back_logo/color

This is the driver-side support needed by PXDiv/Div-Acer-Manager-Max#214, which fixes PXDiv/Div-Acer-Manager-Max#198.

Sysfs interface

Accepted formats:

RRGGBB,brightness,enable
RRGGBB,brightness

• RRGGBB: exactly six hexadecimal characters.
• brightness: integer from 0 to 100.
• enable: optional 0 or 1.
• If enable is omitted, non-zero brightness enables the logo.
• When enable=0, brightness is normalized to 0 to ensure firmware that ignores the enable flag still switches the logo off.

Example:

echo '00ffcc,100,1' | sudo tee /sys/module/linuwu_sense/drivers/platform:acer-wmi/acer-wmi/back_logo/color
cat /sys/module/linuwu_sense/drivers/platform:acer-wmi/acer-wmi/back_logo/color

Implementation

• Adds the PHN16-72 back-logo quirk and capability flag.
• Uses the dedicated back-logo WMI set/get methods with a unified-backlight fallback.
• Strictly rejects malformed RGB, out-of-range brightness/enable values, and extra fields.
• Creates and independently removes the back_logo sysfs group during probe/remove.
• Adds root:linuwu_sense group access through tmpfiles (0660).
• Documents the interface and usage in the README.

Hardware verification

Item	Value
Model	Acer Predator PHN16-72
System version	V1.16
Board	EQE_RTX
BIOS	V1.16
OS	Omarchy (Arch Linux)
Kernel	7.1.9-arch1-2
Tested commit	c425e3372a54e97e56976765449a0009e6d8f73b

Test results

• make W=1 completed successfully and produced a module matching the running kernel.
• make install completed with exit code 0.
• The module loaded and exposed back_logo/color on real PHN16-72 hardware.
• Writing 00ffcc,100,1 changed the physical rear logo to cyan and read back exactly.
• The two-field form ff00aa,40 inferred enable=1, changed the physical logo to magenta, and read back ff00aa,40,1.
• Writing 00ffcc,100,0 physically switched the logo off and correctly read back the normalized state 00ffcc,0,0.
• Invalid RGB, brightness above 100, enable outside 0/1, and unexpected extra fields were rejected while preserving the previous state.
• Module unload removed the sysfs path cleanly; reload recreated it without a kernel Oops, call trace, or panic.
• The okal user received direct read/write access through the linuwu_sense group.
• Automatic module loading, sysfs creation, permissions, and service state all passed after a fresh reboot.

make W=1 emits one existing unrelated warning for the unused quirk_acer_nitro_anv16_41 variable; no back-logo-related build warning was emitted.

Visual evidence

Terminal evidence and real-hardware photos for cyan, disabled, and magenta states are provided in the follow-up PR comment.

Scope

The feature is gated behind the PHN16-72 quirk, so other models do not expose the new sysfs group unless they explicitly gain the capability.

Attribution

The PHN16-72 back-logo WMI protocol is adapted from Nekro-Sense.

[0PeterAdel]

Hardware verification update

Retested the latest PR head (c425e3372a54e97e56976765449a0009e6d8f73b) on real Acer Predator PHN16-72 hardware running Omarchy with kernel 7.1.9-arch1-2.

Physical hardware results

Cyan — 00ffcc,100,1

Disabled — 00ffcc,100,0 → normalized readback 00ffcc,0,0

Magenta at 40% — two-field input ff00aa,40 → inferred ff00aa,40,1

Terminal evidence

Build

Runtime, sysfs, and permissions

Strict invalid-input rejection

Firmware-safe disable normalization

Safe unload/reload cycle

Automatic loading after reboot

Result

• Build and installation passed.
• Valid writes changed the physical rear logo and read back correctly.
• Invalid inputs were rejected without changing the previous state.
• Disable, optional enable inference, group permissions, unload/reload cleanup, and boot persistence passed.
• No kernel Oops, call trace, general-protection fault, or panic was logged during testing.

[0PeterAdel]

Hi @PXDiv, gentle review ping when you have time.

I could not find a CONTRIBUTING.md or CODEOWNERS file in this repository, so I am keeping the update here. This is the driver-side support needed by PXDiv/Div-Acer-Manager-Max#214, which implements the app/daemon UI for the PHN16-72 rear logo request in PXDiv/Div-Acer-Manager-Max#198.

Current status:

• Mergeable, with no unresolved review threads.
• Tested on real Acer Predator PHN16-72 hardware.
• Adds a model-gated back_logo/color sysfs interface.
• Valid cyan, magenta, disable, unload/reload, permissions, and reboot persistence cases are shown in the evidence above.
• Invalid input is rejected while preserving the previous hardware state.
• Scope is limited to PHN16-72 through ACER_CAP_BACK_LOGO.

Happy to split or simplify the patch further if there is a preferred kernel-driver style for this repo.