Re: [REGRESSION] ACPI: PCI: misleading _OSC failure message when _OSC is absent

[Rafael J. Wysocki (Intel)]

On Fri, Jul 24, 2026 at 1:15 PM KONDO KAZUMA(近藤　和真)
<kazuma-kondo@xxxxxxx> wrote:
>
> Hello,
>
> On 2026/07/18 1:22, Rafael J. Wysocki (Intel) wrote:
> > Hi,
> >
> > On Fri, Jul 17, 2026 at 2:01 PM KONDO KAZUMA(近藤　和真)
> > <kazuma-kondo@xxxxxxx> wrote:
> >>
> >> Hello,
> >>
> >> After 7d703df7f4f5 ("ACPI: bus: Split _OSC evaluation out of acpi_run_osc()"),
> >> AE_NOT_FOUND from acpi_evaluate_object() is handled as AE_ERROR in
> >> negotiate_os_control().
> >>
> >> I haven't yet observed any functional issue with this change,
> >> but I started seeing the following misleading messages on my Intel servers:
> >>
> >>     kernel: ACPI: Enabled 2 GPEs in block 00 to 7F
> >>     kernel: ACPI: PCI Root Bridge [UNC0] (domain 0000 [bus fe])
> >>     kernel: acpi PNP0A03:00: _OSC: OS supports [ExtendedConfig ASPM ClockPM Segments MSI EDR HPX-Type3]
> >>   + kernel: acpi PNP0A03:00: _OSC: OS requested [PCIeHotplug SHPCHotplug PME AER PCIeCapability LTR DPC]
> >>   + kernel: acpi PNP0A03:00: _OSC: platform willing to grant [PCIeHotplug SHPCHotplug PME AER PCIeCapability LTR DPC]
> >>   + kernel: acpi PNP0A03:00: _OSC: platform retains control of PCIe features (AE_ERROR)
> >>     kernel: PCI host bridge to bus 0000:fe
> >>
> >> Before the commit, the log was:
> >>
> >>     kernel: ACPI: Enabled 2 GPEs in block 00 to 7F
> >>     kernel: ACPI: PCI Root Bridge [UNC0] (domain 0000 [bus fe])
> >>     kernel: acpi PNP0A03:00: _OSC: OS supports [ExtendedConfig ASPM ClockPM Segments MSI EDR HPX-Type3]
> >>     kernel: PCI host bridge to bus 0000:fe
> >>
> >> "UNC0" is an uncore root bridge and does not define an _OSC method in the ACPI
> >> namespace on my systems.
> >>
> >> Previously, when acpi_evaluate_object() was called for UNC0._OSC, it returned
> >> AE_NOT_FOUND, and that status was propagated to negotiate_os_control().
> >>
> >> Now, it appears that acpi_eval_osc()/acpi_run_osc() no longer preserve the
> >> distinction between AE_NOT_FOUND and other errors from acpi_evaluate_object(),
> >> so negotiate_os_control() no longer receives AE_NOT_FOUND in this case.
> >>
> >> The call chain looks like this on my system:
> >>
> >> negotiate_os_control()
> >>   acpi_pci_osc_control_set()       [retval = AE_ERROR    ]
> >>     acpi_pci_query_osc ()          [retval = AE_ERROR    ]
> >>       acpi_pci_run_osc()           [retval = AE_ERROR    ]
> >>         acpi_run_osc()             [retval = AE_ERROR    ]
> >>           acpi_eval_osc()          [retval = -ENODATA    ]
> >>             acpi_evaluate_object() [retval = AE_NOT_FOUND]
> >>
> >> As a result, negotiate_os_control() logs messages as if the OS had negotiated
> >> with the platform via _OSC, even though _OSC is absent and no such negotiation
> >> actually happens.
> >
> > Fortunately though this only affects the printing of messages and only
> > in the non-PCIe case.
> >
> >> I'm not very familiar with the ACPI/PCI code, so I may be missing some
> >> context. However, if my understanding is correct, would preserving
> >> AE_NOT_FOUND here (for example, having acpi_eval_osc()/acpi_run_osc() return
> >> the error as-is) be the right direction, or should the message handling be
> >> adjusted instead?
> >>
> >> If there is a preferred direction for fixing this, I would be happy to try
> >> putting together a patch and testing it on my system.
> >
> > I cannot send you a proper patch ATM (sorry about that), but please
> > try to replace the
> >
> > (status == AE_NOT_FOUND && !is_pcie(root))
> >
> > check in negotiate_os_control() with the following one:
> >
> > (!is_pcie(root) && !acpi_has_method(handle, "_OSC"))
> >
> > and see if that helps.
>
> Sorry for the late reply.
>
> With the change you suggested, the failure message no longer appears.
> If that's okay with you, I'd like to submit it as a patch.

I think that it'd be better to do this check earlier, even at the
beginning of negotiate_os_control(), because it is pointless to
prepare for evaluating _OSC if it is not present.

So I would add

if (!is_pcie(root) && !acpi_has_method(handle, "_OSC")) {
        print a diagnostic message;
        return;
}

to negotiate_os_control() after the x86_apple_machine check and remove
the (status == AE_NOT_FOUND && !is_pcie(root)) check that would become
redundant then.

Feel free to send a patch doing so.

Thanks!