linux-kernel - Re: [PATCH] PCI: Disable upstream port PTM during suspend

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Date:   Tue, 16 Aug 2022 13:55:55 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     bhelgaas@...gle.com, koba.ko@...onical.com,
        "David E . Box" <david.e.box@...ux.intel.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Disable upstream port PTM during suspend

On Wed, Jul 06, 2022 at 08:32:44PM +0800, Kai-Heng Feng wrote:
> On Intel Alder Lake platforms, Thunderbolt entering D3cold can cause
> some errors reported by AER:
> pcieport 0000:00:1d.0: AER: Uncorrected (Non-Fatal) error received: 0000:00:1d.0
> pcieport 0000:00:1d.0: PCIe Bus Error: severity=Uncorrected (Non-Fatal), type=Transaction Layer, (Requester ID)
> pcieport 0000:00:1d.0:   device [8086:7ab0] error status/mask=00100000/00004000
> pcieport 0000:00:1d.0:    [20] UnsupReq               (First)
> pcieport 0000:00:1d.0: AER:   TLP Header: 34000000 08000052 00000000 00000000
> thunderbolt 0000:0a:00.0: AER: can't recover (no error_detected callback)
> xhci_hcd 0000:3e:00.0: AER: can't recover (no error_detected callback)
> pcieport 0000:00:1d.0: AER: device recovery failed
> 
> In addition to that, it can also block system from suspending when
> a Thunderbolt dock is attached to the same system.
> 
> The original approach [1] is to disable AER and DPC when link is in
> L2/L3 Ready, L2 and L3, but Bjorn identified the root cause is the Unsupported
> Request:
>   - 08:00.0 sent a PTM Request Message (a Posted Request)
>   - 00:1d.0 received the PTM Request Message
>   - The link transitioned to DL_Down
>   - Per sec 2.9.1, 00:1d.0 discarded the Request and reported an
>     Unsupported Request
>   - Or, per sec 6.21.3, if 00:1d.0 received a PTM Request when its
>     own PTM Enable was clear, it would also be treated as an
>     Unsupported Request
> 
> And further: 'David did something like this [1], but just for Root Ports. That
> looks wrong to me because sec 6.21.3 says we should not have PTM enabled in an
> Upstream Port (i.e., in a downstream device like 08:00.0) unless it is already
> enabled in the Downstream Port (i.e., in the Root Port 00:1d.0).'
> 
> So also disable upstream port PTM to make the PCI driver conform to the spec
> and solve the issue.
> 
> [1] https://lore.kernel.org/all/20220408153159.106741-1-kai.heng.feng@canonical.com/
> [2] https://lore.kernel.org/all/20220422222433.GA1464120@bhelgaas/
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215453
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216210
> Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: David E. Box <david.e.box@...ux.intel.com>
> Cc: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>

Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>