linux-kernel - Re: [PATCH] PCI/ASPM: Should not report ASPM support to BIOS if FADT indicates ASPM is unsupported

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Date:   Fri, 15 Jul 2022 14:24:39 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Manyi Li <limanyi@...ontech.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rajat Jain <rajatja@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vidya Sagar <vidyas@...dia.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH] PCI/ASPM: Should not report ASPM support to BIOS if FADT
 indicates ASPM is unsupported

On Fri, Jul 15, 2022 at 9:40 AM Manyi Li <limanyi@...ontech.com> wrote:
>
>
>
> On 2022/7/14 11:20, Kai-Heng Feng wrote:
> > [+Cc Matthew]
> >
> > On Thu, Jul 14, 2022 at 2:28 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
> >>
> >> [+cc Kai-Heng, Vidya, who also have ASPM patches in flight]
> >>
> >> On Wed, Jul 13, 2022 at 07:26:12PM +0800, Manyi Li wrote:
> >>> Startup log of ASUSTeK X456UJ Notebook show:
> >>> [    0.130563] ACPI FADT declares the system doesn't support PCIe ASPM, so disable it
> >>> [   48.092472] pcieport 0000:00:1c.5: PCIe Bus Error: severity=Corrected, type=Physical Layer, (Receiver ID)
> >>> [   48.092479] pcieport 0000:00:1c.5:   device [8086:9d15] error status/mask=00000001/00002000
> >>> [   48.092481] pcieport 0000:00:1c.5:    [ 0] RxErr
> >>> [   48.092490] pcieport 0000:00:1c.5: AER: Corrected error received: 0000:00:1c.5
> >>> [   48.092504] pcieport 0000:00:1c.5: AER: can't find device of ID00e5
> >>> [   48.092506] pcieport 0000:00:1c.5: AER: Corrected error received: 0000:00:1c.5
> >>
> >> Can you elaborate on the connection between the FADT ASPM bit and the
> >> AER logs above?
>
> Sorry,I don't know about that.
>
> >>
> >> What problem are we solving here?  A single corrected error being
> >> logged?  An infinite stream of errors?  A device that doesn't work at
> >> all?
> >
> > Agree, what's the real symptom of the issue?
>
> Please see the details of this issus:
> https://bugzilla.kernel.org/show_bug.cgi?id=216245
>
> >
> >>
> >> We don't need the dmesg timestamps unless they contribute to
> >> understanding the problem.  I don't think they do in this case.
> >
> > According to commit 387d37577fdd ("PCI: Don't clear ASPM bits when the
> > FADT declares it's unsupported"), the bit means "just use the ASPM
> > bits handed over by BIOS".
> >
> > However, I do wonder why both drivers/pci/pci-acpi.c and
> > drivers/acpi/pci_root.c are doing the ACPI_FADT_NO_ASPM check,

Because pci_root.c doesn't read aspm_disabled.

> > maybe one of them should be removed?

Arguably, pci_root.c could look at aspm_disabled instead of looking at
the FADT flag directly.

> I think duplicate work has been done, but comment
> in drivers/acpi/pci_root.c is
> * We want to disable ASPM here, but aspm_disabled
> * needs to remain in its state from boot so that we
> * properly handle PCIe 1.1 devices.  So we set this
> * flag here, to defer the action until after the ACPI
> * root scan.
>
> I don't understand this logic.

This is about the case after failing acpi_pci_osc_control_set() and
generally we need to defer setting aspm_disabled because of
pcie_aspm_sanity_check().

> >
> >>
> >>> Signed-off-by: Manyi Li <limanyi@...ontech.com>
> >>> ---
> >>>   drivers/pci/pcie/aspm.c | 1 +
> >>>   1 file changed, 1 insertion(+)
> >>>
> >>> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> >>> index a96b7424c9bc..b173d3c75ae7 100644
> >>> --- a/drivers/pci/pcie/aspm.c
> >>> +++ b/drivers/pci/pcie/aspm.c
> >>> @@ -1359,6 +1359,7 @@ void pcie_no_aspm(void)
> >>>        if (!aspm_force) {
> >>>                aspm_policy = POLICY_DEFAULT;
> >>>                aspm_disabled = 1;
> >>> +             aspm_support_enabled = false;
> >>
> >> This makes pcie_no_aspm() work the same as booting with
> >> "pcie_aspm=off".  That might be reasonable.
> >>
> >> I do wonder why we need both "aspm_disabled" and
> >> "aspm_support_enabled".  And I wonder why we need to set "aspm_policy"
> >> when we're disabling ASPM.  But those aren't really connected to your
> >> change here.
> >
> >  From what I can understand "aspm_disabled" means "don't touch ASPM
> > left by BIOS", and "aspm_support_enabled" means "whether ASPM is
> > disabled via command line".
> > There seems to be some overlaps though.
>
> According to commit 8b8bae901ce23 ("PCI/ACPI: Report ASPM support to
> BIOS if not disabled from command line"), "aspm_support_enabled" means
> whether or not report ASPM support to the BIOS through _OSC.

Right.