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

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Message-Id: <20220706123244.18056-1-kai.heng.feng@canonical.com>
Date:   Wed,  6 Jul 2022 20:32:44 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     bhelgaas@...gle.com
Cc:     mika.westerberg@...ux.intel.com, koba.ko@...onical.com,
        Kai-Heng Feng <kai.heng.feng@...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: [PATCH] PCI: Disable upstream port PTM during suspend

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>
---
 drivers/pci/pci.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index cfaf40a540a82..8ba8a0e12946e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2717,7 +2717,8 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
 	 * port to enter a lower-power PM state and the SoC to reach a
 	 * lower-power idle state as a whole.
 	 */
-	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
+	    pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM)
 		pci_disable_ptm(dev);
 
 	pci_enable_wake(dev, target_state, wakeup);
@@ -2775,7 +2776,8 @@ int pci_finish_runtime_suspend(struct pci_dev *dev)
 	 * port to enter a lower-power PM state and the SoC to reach a
 	 * lower-power idle state as a whole.
 	 */
-	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
+	    pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM)
 		pci_disable_ptm(dev);
 
 	__pci_enable_wake(dev, target_state, pci_dev_run_wake(dev));
-- 
2.36.1