Fan Control Success on IBM T40? (another quick Q)

[Nate Lawson]

On Wed, 28 Apr 2004, Jeffrey Katcher wrote:
> >From everything I've seen (on the linux-acpi lists), the T40 doesn't have _any_
> fan control in the DSDT.  Apparently it's explicitly controlled via SMBIOS.
> There's a SMAPI interface available from FreeBSD, but I don't have enough info
> yet to exploit it.

That's similar to my T23.  It actually handles fans automatically with SMM
code and does not export the info through ACPI.

> Second question, still on power/clock issues, but diverging a little from ACPI:
> What's the interaction between SpeedStep clock and ACPI clock percentage?
> If I start on batteries, apparently the clock is at 600Mhz (even though dmesg
> reports it as 1600Mhz no matter what).  ACPI CPU then can reduce this base by
> eighths?  So if I start on AC, it's eighths of 1600 and DC, it's eighths of
> 600?

SpeedStep and ACPI performance states are clock/voltage.  Throttling is a
% of the current clock.  So they are additive.  I'm working on a cpufreq
driver for the former and acpi_cpu supports the latter currently.
Thinkpads automatically switch SpeedStep based on AC line at boot time so
if I boot with the AC line unplugged, I get the lowest clock/voltage
combo.  Throttling, if activated, would be in addition to that.

So if your chipset, like mine, offers 1 Ghz and 733 Mhz clock/voltage
settings, and 100% and 50% throttling settings, you have four actual
settings:

1000 mhz
733 mhz
500 mhz (1 ghz + 50% throttle)
366 mhz (733 mhz + 50% throttle)

You won't be able to adjust SpeedStep-like settings until the cpufreq
driver is finished.  It will automatically combine the two additive
settings and export a unified interface that just allows you to select the
clock rate.

-Nate