On 27/04/11(Wed) 12:41, Martin Pieuchot wrote:
> On 26/04/11(Tue) 18:29, Martin Pieuchot wrote:
> > The following diff adds support for dfs. It requires my precedent patch
> > about GPIOs. I don't have a machine with a MPC7448 so it's only tested
> > with a MPC7447A.
> >
> > I'm also interested in various device-tree dumps for further development.
> > If you can send me yours, contact me off list.
>
> Updated diff, correct the voltage offset in case the value of the reg
> property is relative to the gpio controller offset.
As pointed by landry@ I didn't explain what's dfs. Dynamic Frequency
Switching, aka dfs, is a feature available (at least) in the MPC7447A
and MPC7448 processors that adds the ability to divide the processor bus
ratio. Concretely it allows you to reduce the speed and power consumption
on some Apple G4 machine.
For example, the difference here on an ibook G4:
-hw.sensors.adt0.volt1=1.54 VDC (Vccp)
+hw.sensors.adt0.volt1=1.29 VDC (Vccp)
hw.sensors.adt0.volt2=3.28 VDC (Vcc)
hw.sensors.adt0.volt3=0.00 VDC (+5V)
hw.sensors.adt0.volt4=0.00 VDC (+12V)
-hw.cpuspeed=1333
-hw.setperf=100
+hw.cpuspeed=666
+hw.setperf=0
You can check if your machine supports it by looking for the
cpu-vcore-select node in your openfirmware dump:
$ eeprom -p |grep vcore
Regards,
Martin
