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Date:   Fri, 16 Jun 2023 17:01:25 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc:     bhelgaas@google.com, Mario Limonciello <mario.limonciello@amd.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Vidya Sagar <vidyas@nvidia.com>,
        Michael Bottini <michael.a.bottini@linux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PCI/ASPM: Enable ASPM on external PCIe devices
Message-ID: <20230616220125.GA1555182@bhelgaas>
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In-Reply-To: <20230615070421.1704133-1-kai.heng.feng@canonical.com>
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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.  

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?

I don't see any PTM differences there.

Bjorn