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SubjectRe: [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:

What's the connection with Thunderbolt? I see "thunderbolt
0000:0a:00.0" in dmesg, but I think we see that message only because
0a:00.0 happens to be in the hierarchy below the 00:1d.0 Root Port,
not specifically because it's a Thunderbolt device.

Here's the hierarchy:

0000:00:1d.0 Root Port to [bus 08-71]
0000:08:00.0 Switch Upstream Port to [bus 09-71]
0000:09:00.0 Switch Downstream Port to [bus 0a]
0000:0a:00.0 Endpoint (USB controller)
0000:09:01.0 Switch Downstream Port to [bus 0b-3d]
0000:09:02.0 Switch Downstream Port to [bus 3e]
0000:3e:00.0 Endpoint (USB controller)
0000:09:03.0 Switch Downstream Port to [bus 3f-71]

The error logged by 00:1d.0 is an Unsupported Request with Requester
ID 08:00.0.

I think the only relevant thing is that 08:00.0 has PTM enabled and
00:1d.0 has PTM disabled because pci_prepare_to_sleep() only disables
PTM for Root Ports. The same thing could happen if 08:00.0 were an
Endpoint or a non-Thunderbolt Switch Upstream Port.

Is entering D3cold relevant here? I don't know how to tell from dmesg
that we're entering D3cold. If we actually put 08:00.0 in D3cold, I
don't think we would see the Unsupported Request because 08:00.0 can't
send PTM requests from D3cold.

> 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@google.com>
> Cc: David E. Box <david.e.box@linux.intel.com>
> Cc: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>
>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.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));

What do you think of the following possible rework? I think it's
functionally the same except that it disables PTM on Endpoints as well
as Switch Upstream Ports.


diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 95bc329e74c0..96487a9ce5bf 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2707,14 +2707,19 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
return -EIO;

/*
- * There are systems (for example, Intel mobile chips since Coffee
- * Lake) where the power drawn while suspended can be significantly
- * reduced by disabling PTM on PCIe root ports as this allows the
- * port to enter a lower-power PM state and the SoC to reach a
- * lower-power idle state as a whole.
+ * We want to disable PTM on Root Ports because that allows some
+ * chips, e.g., Intel mobile chips since Coffee Lake, to enter a
+ * lower-power PM state.
+ *
+ * PCIe r6.0, sec 2.2.8, strongly recommends that functions support
+ * generation of messages in non-D0 states, so we assume Switch
+ * Upstream Ports or Endpoints may send PTM Requests while in D1,
+ * D2, and D3hot. A PTM message received by a Downstream Port
+ * (including a Root Port) with PTM disabled must be treated as an
+ * Unsupported Request (sec 6.21.3). To prevent this error,
+ * disable PTM in *all* devices, not just Root Ports.
*/
- if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
- pci_disable_ptm(dev);
+ pci_disable_ptm(dev);

pci_enable_wake(dev, target_state, wakeup);

@@ -2764,15 +2769,8 @@ int pci_finish_runtime_suspend(struct pci_dev *dev)
if (target_state == PCI_POWER_ERROR)
return -EIO;

- /*
- * There are systems (for example, Intel mobile chips since Coffee
- * Lake) where the power drawn while suspended can be significantly
- * reduced by disabling PTM on PCIe root ports as this allows the
- * 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)
- pci_disable_ptm(dev);
+ /* See rationale above for disabling PTM */
+ pci_disable_ptm(dev);

__pci_enable_wake(dev, target_state, pci_dev_run_wake(dev));

diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
index 368a254e3124..ec338470d13f 100644
--- a/drivers/pci/pcie/ptm.c
+++ b/drivers/pci/pcie/ptm.c
@@ -31,12 +31,18 @@ static void pci_ptm_info(struct pci_dev *dev)

void pci_disable_ptm(struct pci_dev *dev)
{
- int ptm;
+ int type, ptm;
u16 ctrl;

if (!pci_is_pcie(dev))
return;

+ type = pci_pcie_type(dev);
+ if (!(type == PCI_EXP_TYPE_ROOT_PORT ||
+ type == PCI_EXP_TYPE_UPSTREAM ||
+ type == PCI_EXP_TYPE_ENDPOINT))
+ return;
+
ptm = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
if (!ptm)
return;
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