On Sun, May 11, 2008 at 11:03:16AM +0200, Thomas Gleixner wrote:
> On Sun, 11 May 2008, Alistair John Strachan wrote:
> > > Well we don't have to auto-enable the hpet. Simply adding a loud "you
> > > should try the hpet=force option" printk would help a lot of people.
> >
> > I'm a bit confused about the policy here: if we look at the Intel chipset
> > overrides for HPET, they conditionally enable the HPET _without_ the
> > hpet=force option if you have a chipset on the whitelist.
> >
> > If Intel can do this on their chipsets, why is this not being done for the ATI
> > chipsets for which (presumably) AMD have specs?
>
> Well, we have no confirmation for the correctness of the non Intel
> quirks so far. I'm happy to move them into unconditional mode once
> AMD/ATI/NVidia tell us that the HPET is indeed discoverable this way.
>
> > One thing I'd considered was that HPET isn't actually used very often on Intel
> > chipsets because on most recent Intel CPUs the TSC is stable, but I think
>
> Well, stable except for the C-States. We still need a backup clock
> source as TSC is stopping in C3.
>
> > either the Intel quirk should be consistent with the hpet=force usage,
> > or "known correct" HPET overrides should just always be applied.
>
> That's what we do. We have "known correct" for Intel and those which
> work on the patch submitters box w/o confirmation of the
> correctness. I guess the SB400 one can move into the "is correct"
> category, Andreas ???
Sorry for the late reply, but I had to look for the spec in the first
place ;-) and I have done some coding and testing since then.
(Well, the patch was written as a quick hack to get HPET working on my
private laptop.)
The point is that at least some revisions of IXP400/IXP450 have indeed
hardware issues regarding HPET. Thus HPET works only for certain
chip revisions.
Currently I am internally discussing whether it makes sense to enable
(and properly configure) HPET for those chipset revisions.
BTW, if outcome of this discussion is that HPET on IXP400/IXP450
shouldn't be used then IMHO a quirk is needed to reliably disable it.
I.e. disable it even if a system provides an ACPI HPET table.
Thanks for your patience.
Regards,
Andreas