On Mon, 8 Aug 2011, Jukka Ruohonen wrote:
Why?Because we (the operating system) know this better than the BIOS writer. And because this flag is not reliable; numerous systems where tsc(9) is "broken" miss this flag in my ACPI table collection, and vice versa.
This flag is new in ACPI v3.0. If the flag is missing, it does not change behaviour from what the tsc driver did before. If the flag is present, the tsc driver will take the safe approach and prefer the HPET or PM-Timer as per ACPI spec. If you're really really really sure you know more about the platform than the platform code, you can re-enable TSC timecounter at runtime.