Re: [PATCH 1/1] tools/libacpi: clear ASL warning about PCI0

["Ariel Otilibili-Anieli" <Ariel.Otilibili-Anieli@xxxxxxxxxx>]

On Monday, December 16, 2024 12:38 CET, Jan Beulich <jbeulich@xxxxxxxx> wrote:

> On 16.12.2024 12:31, Ariel Otilibili-Anieli wrote:
> > On Monday, December 16, 2024 12:01 CET, Jan Beulich <jbeulich@xxxxxxxx> 
> > wrote:
> > 
> >> On 16.12.2024 11:36, Ariel Otilibili-Anieli wrote:
> >>> On Monday, December 16, 2024 10:53 CET, Jan Beulich <jbeulich@xxxxxxxx> 
> >>> 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.