On Monday, December 16, 2024 12:38 CET, Jan Beulich <jbeul...@suse.com> wrote:
> On 16.12.2024 12:31, Ariel Otilibili-Anieli wrote:
> > On Monday, December 16, 2024 12:01 CET, Jan Beulich <jbeul...@suse.com>
> > wrote:
> >
> >> On 16.12.2024 11:36, Ariel Otilibili-Anieli wrote:
> >>> On Monday, December 16, 2024 10:53 CET, Jan Beulich <jbeul...@suse.com>
> >>> wrote:
> >>>
> >>>> On 15.12.2024 16:40, Ariel Otilibili wrote:
> >>>>> * iasl complains _HID and _ADR cannot be used at the same time
> >>>>>
> >>>>> ```
> >>>>> /usr/bin/iasl -vs -p tools/firmware/hvmloader/dsdt_anycpu.tmp -tc
> >>>>> tools/firmware/hvmloader/dsdt_anycpu.asl 2>&1 | grep -B10 HID
> >>>>> tools/firmware/hvmloader/dsdt_anycpu.asl 40: Device (PCI0)
> >>>>> Warning 3073 - Multiple types ^
> >>>>> (Device object requires either a _HID or _ADR, but not both)
> >>>>> ```
> >>>>>
> >>>>> * generally _HID devices are enumerated and have their drivers loaded
> >>>>> by ACPI
> >>>>> * this is from "ASL 2.0 Introduction and Overview" (page 4).
> >>>>> * removing _ADR, the warning is cleared out.
> >>>>
> >>>> Okay, that's the positive aspect. Yet what about the potential fallout
> >>>> thereof?
> >>>> Can you confirm that there's no risk of regressions with older guest
> >>>> OSes, for
> >>>> example?
> >>>
> >>> OSes that were released after ACPI 2.0 should work [1]; including WinXP:
> >>> The 2.0 specs says either _HID or _ADR should be included [2], not both
> >>> (Section 6.1, page 146).
> >>
> >> We must be looking at two different variants of the spec then. My copy says
> >> "device object must contain either an _HID object or an _ADR object, but
> >> can
> >> contain both." Also still in 2.0c. I agree that in e.g. 6.5 the wording has
> >> changed. I also agree that the use of "either" doesn't help clarity.
> >
> > I looked up 2.0 (July 2000); indeed, it said "can contain both". My bad.
> >>
> >>> I chose WinXP because, on another patch, it came up in the discussion [3].
> >
> > The change should work down to WinXP: the name _HID is kept.
> >
> > ```
> > $ git grep -B2 -A2 -n PNP0A03
> > tools/libacpi/dsdt.asl-40- Device (PCI0)
> > tools/libacpi/dsdt.asl-41- {
> > tools/libacpi/dsdt.asl:42: Name (_HID, EisaId ("PNP0A03"))
> > tools/libacpi/dsdt.asl-43- Name (_UID, 0x00)
> > tools/libacpi/dsdt.asl-44- Name (_ADR, 0x00)
> > ```
> >
> > Its EISA ID is "PNP0A03"; the namespace is reserved for Microsoft.
> > Microsoft identifies "PNP0A03" as PCI devices [1].
>
> You again say "should" without explaining what you derive this from. Is it
> written down somewhere that no OS we (remotely) care about ever evaluated
> _ADR when _HID was there? As before, along side mentioning the benefits of
> the change, I'd like to also see a discussion of risks.
>
I derive this knowledge only from the APCI specs. Indeed, I've not researched
how every OS interprets _HID and _ADR.
>From your answer, I see you would like to be sure the change will introduce no
>regression. I do understand you point of view; keeping the backward
>compatibility.
The benefit is that the warning will be cleared. We agree on that.
The risk is that, if ever any OS relies on _ADR, and cannot read _HID; it would
break.
After thinking about it, the other way is less risky: this _HID name is only
recognized by Windows. Every OS should (I did say it again, should) understand
_ADR.
If you think the change makes sense, I can remove _HID instead of _ADR.
Otherwise, I think we should end the discussion.
Ariel
> Jan
