Over the past week, I have been trying to compile a minimal kernel for an old machine, and I've noticed the exact same behavior you are seeing with your new Gentoo set up when I use ACPI, and the behavior you saw with your Slackware when I use APM.
Specifically, if I compile a kernel with ACPI but not APM:
- Console goes blank, but the display never power downs.
- However, you have control over ACPI events (e.g., pressing the power button initiates the Linux shutdown sequence).
If I compile with only APM, no ACPI:
- When the console goes blank, the display powers down.
- Pressing the power button cuts power to the system immediately.
I made various attempts (setterm, vbetools) to get the screen to power-down during console blanking with ACPI, but can't seem to do it. If anyone has any ideas, please let me know.
Also, I don't think you have to re-compile your kernel to repeat my experiment. I believe most default kernels have both ACPI and APM available (as modules), and defaults to ACPI (if the hardware supports it). To try disabling ACPI, you should be able to pass in acpi=off
to your kernel during boot up.
Per the Linux kernel documentation:
acpi= [HW,ACPI,X86] Advanced Configuration and Power Interface Format: { force | off | strict | noirq | rsdt } force -- enable ACPI if default was off off -- disable ACPI if default was on noirq -- do not use ACPI for IRQ routing strict -- Be less tolerant of platforms that are not strictly ACPI specification compliant. rsdt -- prefer RSDT over (default) XSDT copy_dsdt -- copy DSDT to memory See also Documentation/power/pm.txt, pci=noacpi
(Source: http://www.kernel.org/doc/Documentation/kernel-parameters.txt)