Re: [Regression in 6.14-rc1] System suspend/resume broken by PCI commit 1db806ec06b7c

Rafael J. Wysocki
2025-02-03T20:31:36Z

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On Mon, Feb 3, 2025 at 9:12 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> Hi,
>
> The following commit:
>
> commit 1db806ec06b7c6e08e8af57088da067963ddf117
> Author: Jian-Hong Pan <jhp@endlessos.org>
> Date: Fri Nov 15 15:22:02 2024 +0800
>
> PCI/ASPM: Save parent L1SS config in pci_save_aspm_l1ss_state()
>
> After 17423360a27a ("PCI/ASPM: Save L1 PM Substates Capability for
> suspend/resume"), pci_save_aspm_l1ss_state(dev) saves the L1SS state for
> "dev", and pci_restore_aspm_l1ss_state(dev) restores the state for both
> "dev" and its parent.
>
> The problem is that unless pci_save_state() has been used in some other
> path and has already saved the parent L1SS state, we will restore junk to
> the parent, which means the L1 Substates likely won't work correctly.
>
> Save the L1SS config for both the device and its parent in
> pci_save_aspm_l1ss_state(). When restoring, we need both because L1SS must
> be enabled at the parent (the Downstream Port) before being enabled at the
> child (the Upstream Port).
>
> Link: https://lore.kernel.org/r/20241115072200.37509-3-jhp@endlessos.org
> Fixes: 17423360a27a ("PCI/ASPM: Save L1 PM Substates Capability for
> suspend/resume")
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218394
> Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Signed-off-by: Jian-Hong Pan <jhp@endlessos.org>
> [bhelgaas: parallel save/restore structure, simplify commit log, patch at
> https://lore.kernel.org/r/20241212230340.GA3267194@bhelgaas]
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> Tested-by: Jian-Hong Pan <jhp@endlessos.org> # Asus B1400CEAE
>
> broke system suspend/resume on my Dell XPS13 9360. It doesn't even
> pass suspend/resume testing after "echo devices > /sys/power/pm_test".
>
> It looks like PCIe links are all down during resume after the above
> commit, but it is rather hard to collect any data in that state.
>
> Reverting the above commit on top of 6.14-rc1 makes things work again,
> no problem.
>
> I'm unsure what exactly the problem is ATM, but I'm going to check a
> couple of theories.

The attached change makes it work again, FWIW, but moving the
parent->l1ss check alone below the pdev l1ss saving doesn't help.

So it is either the parent check against NULL or the
pcie_downstream_port(pdev) one that breaks it. I guess the former,
but I'll test it tomorrow.

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---
drivers/pci/pcie/aspm.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)

--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -85,15 +85,7 @@
struct pci_cap_saved_state *save_state;
u32 *cap;

- /*
- * If this is a Downstream Port, we never restore the L1SS state
- * directly; we only restore it when we restore the state of the
- * Upstream Port below it.
- */
- if (pcie_downstream_port(pdev) || !parent)
- return;
-
- if (!pdev->l1ss || !parent->l1ss)
+ if (!pdev->l1ss)
return;

/*
@@ -108,7 +100,7 @@
pci_read_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL2, cap++);
pci_read_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL1, cap++);

- if (parent->state_saved)
+ if (!parent || parent->state_saved || !parent->l1ss)
return;

/*