Fan control for PowerMac7_3 (#3)

H. Peter Anvin hpa at
Sat Oct 16 14:24:05 EST 2004

Benjamin Herrenschmidt wrote:
> Ok, here's a new patch that fixes a few issues, it's been
> tested on a non-liquid cooled system and appear to work ok.

I'm testing it out right now.  It is definitely suffering from some 
degree of oscillation when idling, and it seems to be one particular 
(set of) fan(s) that is having that problem.

Note that one cause of oscillation at low speed is that there is a 
minimum speed below which the fans will simply stop.  This may be what 
is happening here.

Some time later I'll try to figure out which numbers to collect and try 
to generate a graph over time.

It's definitely passing the stress test, though; make -j4 on the whole 
kernel (with the .config posted earlier) took 4:27.19.  The other stress 
test -- which used to kill the old thermal driver dead in a matter of 
seconds -- is to start a bunch of "cat /dev/zero > /dev/null" is happily 
running, and nice and quiet.

The oscillation is obnoxious, though.


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