Virtual machines often use an ACPI power button event to tell the machine to shut down gracefully. Provide an extremely lightweight "tiny power button" driver to handle this event by signaling init directly, rather than running a separate daemon (such as acpid or systemd-logind) that adds to startup time and VM image complexity. I originally proposed a change to the ACPI power button driver to introduce an optional path to signal init, but Rafael expressed a preference to have this as a separate, mutually exclusive driver instead. The result did come out much simpler, conceptually, with the added benefit of being able to disable CONFIG_INPUT entirely for a kernel that exclusively targets cloud/VM systems. The first patch in the series just moves HID definitions to acpi/button.h in preparation for sharing them with the tiny-power-button driver. The second patch provides the driver itself. Josh Triplett (2): acpi: button: move HIDs to acpi/button.h acpi: Add new tiny-power-button driver to directly signal init drivers/acpi/Kconfig | 24 +++++++++++++++++ drivers/acpi/Makefile | 1 + drivers/acpi/button.c | 3 --- drivers/acpi/tiny-power-button.c | 46 ++++++++++++++++++++++++++++++++ include/acpi/button.h | 4 +++ 5 files changed, 75 insertions(+), 3 deletions(-) create mode 100644 drivers/acpi/tiny-power-button.c -- 2.25.0
