linux-kernel - Re: [PATCH] PCI/ASPM: Enable ASPM on external PCIe devices

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Date:   Wed, 21 Jun 2023 11:08:18 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     bhelgaas@...gle.com, Mario Limonciello <mario.limonciello@....com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Vidya Sagar <vidyas@...dia.com>,
        Michael Bottini <michael.a.bottini@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/ASPM: Enable ASPM on external PCIe devices

On Sat, Jun 17, 2023 at 6:01 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Thu, Jun 15, 2023 at 03:04:20PM +0800, Kai-Heng Feng wrote:
> > When a PCIe device is hotplugged to a Thunderbolt port, ASPM is not
> > enabled for that device. However, when the device is plugged preboot,
> > ASPM is enabled by default.
> >
> > The disparity happens because BIOS doesn't have the ability to program
> > ASPM on hotplugged devices.
> >
> > So enable ASPM by default for external connected PCIe devices so ASPM
> > settings are consitent between preboot and hotplugged.
> >
> > On HP Thunderbolt Dock G4, enable ASPM can also fix BadDLLP error:
> > pcieport 0000:00:1d.0: AER: Corrected error received: 0000:07:04.0
> > pcieport 0000:07:04.0: PCIe Bus Error: severity=Corrected, type=Data Link Layer, (Receiver ID)
> > pcieport 0000:07:04.0:   device [8086:0b26] error status/mask=00000080/00002000
> > pcieport 0000:07:04.0:    [ 7] BadDLLP
> >
> > The root cause is still unclear, but quite likely because the I225 on
> > the dock supports PTM, where ASPM timing is precalculated for the PTM.
>
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217557
>
> I know you said this isn't clear yet, but I don't see a connection
> between ASPM being enabled and PTM.  If anything, *disabling* ASPM
> should be safer if there's a timing issue.

If PTM timing is tested when ASPM is enabled, there can be a strong
connection between the two.

I'll raise the issue to IGC devs.

>
> I assume the ASPM timing you refer to is the LTR snoop/no snoop
> latency, since that's the only timing difference I see in the lspci
> output in bugzilla?

Not only LTR. ASPM L0s and L1 are not enabled when devices are hotplugged.

Kai-Heng

>
> I don't see any PTM differences there.
>
> Bjorn