G5 clock frequency scaling

G5 clock frequency scaling

[Arrigo Benedetti]

Does anyone know if the current IBM 970 chips in dual G5 Powermacs and 
Xserves is under any clock frequency
scaling control? In other words, is the clock freuquency always 
guardanteed to be the nominal, or it may change
based on temperature? If this is the case, does the linux kernel have 
any control on it?

Thanks
-Arrigo

Re: G5 clock frequency scaling

[Benjamin Herrenschmidt]

On Tue, 2004-11-02 at 10:28 -0800, Arrigo Benedetti wrote:
> Does anyone know if the current IBM 970 chips in dual G5 Powermacs and 
> Xserves is under any clock frequency
> scaling control? In other words, is the clock freuquency always 
> guardanteed to be the nominal, or it may change
> based on temperature? If this is the case, does the linux kernel have 
> any control on it?

The current desktop models have a "clock slewing" capability which isn't
used by the kernel at this point. So the machine stays at the speed it
had when booting.

However, it's been observed that the firmware tend to boot at max speed
when auto-booting, and at lowest speed (1.3Ghz generally observed) when
entering the OF manual command line interface.

Ben.