Linux 5.7 Getting A "Tiny Power Button" Driver
This ACPI tiny power button driver is not for a physically tiny power button, but rather a simple ACPI power button driver out of Intel intended for virtual machines and more basic than the generic ACPI button driver given the limited scope of VMs.
Virtual machines tend to rely on simulated ACPI power button events for having the VM power off gracefully but can rely on a daemon like acpid or systemd-logind for processing the said event. With the APCI tiny power button driver, the event from the VM is handled directly and immediately signals the init process. The goal of the tiny power button driver is to decrease startup time and reduce VM image complexity.
More details via the patch series. This also serves as a basic example of a Linux kernel driver at just 46 lines of code.