[ltp] [patch 07/11] ibm-acpi: document fan control

[Henrique de Moraes Holschuh]

On Mon, 09 Oct 2006, Shem Multinymous wrote:
> >+ *      6      disengage mode (takes precedence over bit 7);
> >+ *             not available on all thinkpads.  Disables
> >+ *             tachometer, and speeds up fan to 100%
> 
> *slowly* speeds up fan, in my experience. That's exploited by the
> antipulse hack so is perhaps worth mentioning.

Agreed.  I will do so.  I am not sure at all if all ECs act like this, but
the way the T43 behaves it certainly looks like whatever they use to control
PWM is set to never variate more than a few % per second, so if you tell the
fan to change from one duty cycle to another, it takes its sweet time to do
it.  This is standard practice in fan controllers, everyone does it this way
for numerous reasons, so I'd not be too surprised to learn all ThinkPads
back to the 570 do it this way.

> >+ *     5-3     either unused or fan level
> 
> On my T43, setting these is the same as setting fan level 7 (i.e., fan
> level is 0..63 and 7..63 are identical).

The DSDTs on older models show that 0..7 is all that is really supported,
one of them even have just 3 bits set for HFSP in namespace ECOR (EC
operating registers)...  so I'd guess we better leave these as undefined
meaning, and not as "fan level".

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh