Rafael J. Wysocki wrote:
On Wednesday, 26 of December 2007, Linus Torvalds wrote:
On Tue, 25 Dec 2007, Rafael J. Wysocki wrote:
the ACPI specification between versions 1.0x and 2.0. Namely, while ACPI
2.0 and later wants us to put devices into low power states before calling
_PTS, ACPI 1.0x wants us to do that after calling _PTS. Since we're following
the 2.0 and later specifications right now, we're not doing the right thing for
the (strictly) ACPI 1.0x-compliant systems.
We ought to be able to fix things on the high level, by calling _PTS earlier on
systems that claim to be ACPI 1.0x-compliant. That will require us to modify
the generic susped code quite a bit and will need to be tested for some time.
That's insane. Are you really saying that ACPI wants totally different
orderings for different versions of the spec?
Yes, I am.
And does Windows really do that?
I don't know.
Please don't make lots of modifications to the generic suspend code. The
only thing that is worth doing is to just have a firmware callback before
the "device_suspend()" thing (and then on a ACPI-1.0 system, call _PTS
*there*), and on an ACPI-2.0 system, call _PTS *after* device_suspend().
Yes, that's what I'm going to do, but I need to untangle some ACPI code for
this purpose.
Still, the fact is, some (most, I think) drivers *should* put themselves
into D3 only in "late_suspend()", so if ACPI-2.0 really expects _PTS to be
called after that, we're just screwed.
Well, section 9.1.6 of ACPI 2.0 specifies the suspend ordering directly and
says exactly that _PTS is to be executed after putting devices into respective
D states.
I would not take those sections as gospel, they're really an example
only. It's quite possible that Windows does not follow that ordering.
Also, as was pointed out, pre-Vista versions of Windows follow ACPI 1.0
and Vista follows 3.0, so 2.0 doesn't really matter since BIOS people
won't test against it. 1.0 specifies that _PTS is to be called before
suspending devices and 3.0 says that the AML must not depend on any
specific device power state, so in both cases it should be safe to call
_PTS before suspending, no?
--
Robert Hancock Saskatoon, SK, Canada
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