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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan