Re: [PATCH] - Initial dothan speedstep support

[Michael Clark <michael@metaparadigm.com>]

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Hi Dave, Jeremy,

I thought i'd give the ACPI code in speedstep-centrino a try as I wanted
to see what the BIOS freq/voltage tables the vendor was using due to the
apparent choice of voltages (VID#A through VID#C) in the processor specs.

Anyway this is what I found (with the debug code in attached patch):

centrino_cpu_init_acpi: 1800000000 Hz, 1340e-03 volts
centrino_cpu_init_acpi: 1600000000 Hz, 1292e-03 volts
centrino_cpu_init_acpi: 1400000000 Hz, 1228e-03 volts
centrino_cpu_init_acpi: 1200000000 Hz, 1164e-03 volts
centrino_cpu_init_acpi: 1000000000 Hz, 1116e-03 volts
centrino_cpu_init_acpi: 800000000 Hz, 1052e-03 volts
centrino_cpu_init_acpi: 600000000 Hz, 988e-03 volts

It appears the T42 is using the VID#A voltages (the highest) and my
patch was using VID#C (the 2nd from lowest) for which the upper voltage
has the biggest difference being 0.032 volts lower - not much in it.

As I said earlier in my reading of the specs there seemed to be no
guidance on which profile to use aside from the voltage and ripple
tolerance tables.

So the attached patch (in addition to ACPI freq table debug message)
changes the table version to use the VID#A voltage so as to err on the
conservative side of a higher voltage (as the upper voltage max for
the chip is 1.6v) to allow for cases where the error on the voltage
would drop it too low - not sure if just IBM are using this. Would be
interesting to see the ACPI freq/voltage tables for other vendor's
Dothan laptops.

Not sure on whether we should do this although it means we match at least
what one vendor has done? Any ideas? (debug printk may be useful for those
with ACPI and speedstep for debugging incorrect BIOS tables).

Thanks
~mc

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