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SubjectRe: [patch 0/2] suspend/resume regression fixes
On Sunday, 23 September 2007 00:59, Linus Torvalds wrote:
> On Sat, 22 Sep 2007, Thomas Gleixner wrote:
> >
> > My final enlightment was, when I removed the ACPI processor module,
> > which controls the lower idle C-states, right before resume; this
> > worked fine all the time even without all the workaround hacks.
> >
> > I really hope that this two patches finally set an end to the "jinxed
> > VAIO heisenbug series", which started when we removed the periodic
> > tick with the clockevents/dyntick patches.
> Ok, so the patches look fine, but I somehow have this slight feeling that
> you gave up a bit too soon on the "*why* does this happen?" question.
> I realize that the answer is easily "because ACPI screwed up", but I'm
> wondering if there's something we do to trigger that screw-up.
> In particular, I also suspect that this may not really fix the problem -
> maybe it just makes the window sufficiently small that it no longer
> triggers. Because we don't necessarily understand what the real background
> for the problem is, I'm not sure we can say that it is solved.
> The reason I say this is that I have a suspicion on what triggers it.
> I suspect that the problem is that we do
> pm_ops->prepare();
> disable_nonboot_cpus()
> suspend_enter();
> enable_nonboot_cpus()
> pm_finish()
> and here the big thing to notice is that "pm_ops->prepare()" call, which
> sets the wakup vector etc etc.
> So maybe the real problem here is that once we've done the "->prepare()"
> call and ACPI has set up various stuff, we MUST NOT do any calls to any
> ACPI routines to set low-power states, because the stupid firmware isn't
> expecting it.

I think that this is the case.

> Now, if this is the cause, then I think your patch should indeed fix it,
> since you get called by the early-suspend code (which happens *before* the
> "->prepare()" call), but at the same time, I wonder if maybe it would be
> slightly "more correct" to instead of using the suspend/resume callbacks,
> simply do this in the "acpi_pm_prepare()" stage, since that is likely the
> thing that triggers it?
> But hey, I think I'll apply the patches as-is. I'd just feel even better
> if we actually understood *why* doing the CPU Cx states is not something
> we can do around the suspend code!

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