Microsoft’s Hidden ACPI Function Finally Gets Linux Support — Fixing Critical Overheating Bug on Lenovo Laptops

In a significant development for Linux laptop users, Microsoft’s three-year-old “Turn On Display” ACPI Device Specific Method (DSM) is finally making its way into the Linux kernel, potentially resolving a dangerous overheating issue affecting certain Lenovo Yoga laptops.

The story begins with Windows 11 22H2, released in 2022, which introduced a new ACPI function designed to improve the modern standby experience. This Function 9 notification, officially called the “Turn On Display” method, was created to signal firmware during resume from sleep that the operating system intends to activate the display. While this might seem like a minor optimization, it has become crucial for proper hardware operation on some modern laptops.

The plot thickened in August 2025 when a user reported a severe bug on the Linux Kernel Bug Tracker (issue #220505). The problem was alarming: after resuming from suspend, the Lenovo Yoga Slim 7i Aura (15ILL9) would experience complete fan failure, regardless of CPU temperature or system load. The result? CPU temperatures would skyrocket to 95 degrees Celsius during normal tasks, creating a genuine safety hazard. The only solution was a complete system reboot, and remarkably, the same hardware worked perfectly under Windows.

For months, developers were stumped. The issue persisted across multiple kernel versions, and traditional debugging approaches yielded no results. It wasn’t until late last month that the breakthrough came—the missing piece was Microsoft’s Function 9 notification.

Jakob Riemenschneider, the developer who identified and implemented the fix, provided crucial insight into why this function matters. According to Microsoft’s documentation, Function 9 serves as an “intent” signal, allowing firmware to release power limits earlier when the OS plans to turn on the display. On the affected Lenovo Yoga model, the Embedded Controller (EC) turns off components like fans and keyboard backlights during sleep but requires this specific notification to wake them up again.

The technical implementation is elegant in its simplicity. The patch defines a new function index (ACPI_MS_TURN_ON_DISPLAY) and integrates it into the ACPI s2idle driver’s resume sequence. The execution order follows a logical progression:

1. LPS0 Exit (Function 6) – Exit the low-power idle state
2. Turn On Display Intent (Function 9) – Signal display activation intent
3. Modern Standby Exit (Function 8) – Complete the standby exit process
4. Screen On (Function 4) – Actually turn on the display

This ordering is critical because it gives the firmware time to restore power rails and functionality before the software fully exits the sleep state. By invoking Function 9 before the Modern Standby Exit, the system ensures that fans and other components are reactivated in time to prevent overheating.

The patch has been queued into the Linux power management subsystem’s “linux-next” Git branch, positioning it for inclusion in the upcoming Linux 6.20~7.0 kernel cycle. This means users won’t have to wait long for the fix to reach stable releases.

However, this development raises broader questions about the evolving relationship between operating systems and hardware firmware. Microsoft introduced this function three years ago, and it’s only now becoming necessary for proper Linux operation. This suggests that hardware manufacturers are increasingly designing their firmware with Windows-specific behaviors in mind, potentially creating compatibility challenges for alternative operating systems.

The implications extend beyond just one laptop model. Given that this behavior has been observed on at least one device, it’s likely that other laptops with similar firmware implementations may face comparable issues under Linux. As more hardware adopts these Windows-specific optimizations, Linux support for such functions may become increasingly important for ensuring proper functionality.

For Linux users with affected hardware, this fix represents more than just a convenience—it’s a critical safety improvement that prevents potentially dangerous overheating scenarios. The fact that a missing ACPI call could cause complete fan failure demonstrates how tightly integrated modern hardware and software have become, and how seemingly minor omissions can have major consequences.

As the Linux kernel continues to evolve and adapt to these hardware-specific requirements, we can expect to see more cases where Windows-introduced features become necessary for proper cross-platform support. This particular case serves as a reminder that the open-source community must remain vigilant and responsive to the changing landscape of hardware design, even when those changes originate from proprietary systems.

Tags: Linux Kernel, ACPI, Microsoft Windows 11, Lenovo Yoga, overheating fix, modern standby, device specific method, firmware compatibility, kernel development, laptop hardware, thermal management, open source, cross-platform support

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