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SubjectRe: BIOS Flash changes PowerNOW frequencies?
On Sun, Jan 11, 2004 at 12:56:10PM -0500, Mark W. Alexander wrote:
> I'm not currently subscribed. Please cc: me on responses.
> I'm running 2.6.0 on an HP Pavilion ze4420 Athlon version (lspci -v below). I
> recently flashed the BIOS (hoping against all odds for suspend to ram
> capability) and the CPU frequencies discovered by PowerNOW (K7) has changed.
> This is obviously caused by the BIOS update, but the stupid question of the day
> is "Why?". If the CPU and chipset support both sets of frequencies with
> different BIOS, wouldn't the _real_ set of supported frequencies be the union
> of the 2?

In reality, yes.
However BIOS programmers have a different perception of reality to the rest of us.
The spec for PST tables allows for up to 256 FID/VID pairs, yet everyone just
seems to offer 5-6 as maximum. I guess they figured no-one needed the granularity
of the full range.

> As startling as it was to come up at 532Mhz the first boot, I can see where
> this could provide some dramatic power savings (say, while using vi),
> but the now missing 1064, 1463 and 1596 frequencies were more practical
> for actually doing something worthwhile (say, using vi while watching a
> DVD ;).
> Is there anything I can do to persuade PowerNOW/frequency scaling to see the
> full range of frequencies that I've seen this box can do?

Something that has been planned for quite a while has been a means of overriding
the tables using sysfs. I haven't had time to implement this, and no-one else
has found the time/motivation to do so either it seems.

Something I was tempted to do at one point (due to the number of broken PST's out
there) was to offer a 'ignore_pst' module parameter, which exposed the full table
to sysfs. The only problem being some VRMs can't handle certain frequencies at
certain voltages whilst some can, making it hard to find a set of 'safe' values
for each frequency.

How to find out which one VRM can handle frequency X at voltage Y ?
Through the PST tables.

*sigh*, back to the drawing board.


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