on the previous generation of Pentium-M processors (Banias). Support for
Dothan and later processors involves working with acpi_perf(4) to extract
information about supported states. This driver should work on MP systems
including HTT. It is experimental and may have a few bugs but has been
tested to not crash at least.
Thanks to Colin Percival for his initial work on this driver.
reboot. Safter the reboot the TCC is usually in the Automatic mode, in which
reading current performance level is likely to produce bogus results make sure
to switch it to the On-Demand mode and set to some known performance level.
Unfortunately there is no reliable way to check that TCC is in the Automatic
mode. Reading bit 4 of ACPI Thermal Monitor Control Register produces 0
regardless of the current mode.
MFC after: 1 week
Suggested by: nate
- get rid of "magick" values in code and make sysctl's reflecting reality
on processor versions which have one or another frequency "forbidden"
due to errata.
MFC after: 2 weeks
CPU_ENABLE_TCC enables Thermal Control Circuitry (TCC) found in some
Pentium(tm) 4 and (possibly) later CPUs. When enabled and detected,
TCC allows to restrict power consumption by using machdep.cpuperf*
sysctls. This operates independently of SpeedStep and is useful on
systems where other mechanisms such as apm(4) or acpi(4) don't work.
Given the fact that many, even modern, notebooks don't work properly
with Intel ACPI, this is indeed very useful option for notebook owners.
Obtained from: OpenBSD
MFC after: 2 weeks
