Re: [PATCH v4] PCI/PM: Prevent runtime suspend before devices are fully initialized

Rafael J. Wysocki
2026-01-19T12:26:39Z

On Mon, Jan 19, 2026 at 11:01 AM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> On 18.01.2026 12:59, Rafael J. Wysocki wrote:
> > On Sun, Jan 18, 2026 at 12:53 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >> On Sat, Jan 17, 2026 at 2:19 AM Brian Norris <briannorris@chromium.org> wrote:
> >>> On Thu, Jan 15, 2026 at 12:14:49PM +0100, Marek Szyprowski wrote:
> >>>> On 14.01.2026 21:10, Brian Norris wrote:
> >>>>> On Wed, Jan 14, 2026 at 10:46:41AM +0100, Marek Szyprowski wrote:
> >>>>>> On 06.01.2026 23:27, Bjorn Helgaas wrote:
> >>>>>>> On Thu, Oct 23, 2025 at 02:09:01PM -0700, Brian Norris wrote:
> >>>>>>>> Today, it's possible for a PCI device to be created and
> >>>>>>>> runtime-suspended before it is fully initialized. When that happens, the
> >>>>>>>> device will remain in D0, but the suspend process may save an
> >>>>>>>> intermediate version of that device's state -- for example, without
> >>>>>>>> appropriate BAR configuration. When the device later resumes, we'll
> >>>>>>>> restore invalid PCI state and the device may not function.
> >>>>>>>>
> >>>>>>>> Prevent runtime suspend for PCI devices by deferring pm_runtime_enable()
> >>>>>>>> until we've fully initialized the device.
> >>>>> ...
> >>>>>> This patch landed recently in linux-next as commit c796513dc54e
> >>>>>> ("PCI/PM: Prevent runtime suspend until devices are fully initialized").
> >>>>>> In my tests I found that it sometimes causes the "pci 0000:01:00.0:
> >>>>>> runtime PM trying to activate child device 0000:01:00.0 but parent
> >>>>>> (0000:00:00.0) is not active" warning on Qualcomm Robotics RB5 board
> >>>>>> (arch/arm64/boot/dts/qcom/qrb5165-rb5.dts). This in turn causes a
> >>>>>> lockdep warning about console lock, but this is just a consequence of
> >>>>>> the runtime pm warning. Reverting $subject patch on top of current
> >>>>>> linux-next hides this warning.
> >>>>>>
> >>>>>> Here is a kernel log:
> >>>>>>
> >>>>>> pci 0000:01:00.0: [17cb:1101] type 00 class 0xff0000 PCIe Endpoint
> >>>>>> pci 0000:01:00.0: BAR 0 [mem 0x00000000-0x000fffff 64bit]
> >>>>>> pci 0000:01:00.0: PME# supported from D0 D3hot D3cold
> >>>>>> pci 0000:01:00.0: 4.000 Gb/s available PCIe bandwidth, limited by 5.0
> >>>>>> GT/s PCIe x1 link at 0000:00:00.0 (capable of 7.876 Gb/s with 8.0 GT/s
> >>>>>> PCIe x1 link)
> >>>>>> pci 0000:01:00.0: Adding to iommu group 13
> >>>>>> pci 0000:01:00.0: ASPM: default states L0s L1
> >>>>>> pcieport 0000:00:00.0: bridge window [mem 0x60400000-0x604fffff]: assigned
> >>>>>> pci 0000:01:00.0: BAR 0 [mem 0x60400000-0x604fffff 64bit]: assigned
> >>>>>> pci 0000:01:00.0: runtime PM trying to activate child device
> >>>>>> 0000:01:00.0 but parent (0000:00:00.0) is not active
> >>>>> Thanks for the report. I'll try to look at reproducing this, or at least
> >>>>> getting a better mental model of exactly why this might fail (or,
> >>>>> "warn") this way. But if you have the time and desire to try things out
> >>>>> for me, can you give v1 a try?
> >>>>>
> >>>>> https://lore.kernel.org/all/20251016155335.1.I60a53c170a8596661883bd2b4ef475155c7aa72b@changeid/
> >>>>>
> >>>>> I'm pretty sure it would not invoke the same problem.
> >>>> Right, this one works fine.
> >>>>
> >>>>> I also suspect v3
> >>>>> might not, but I'm less sure:
> >>>>>
> >>>>> https://lore.kernel.org/all/20251022141434.v3.1.I60a53c170a8596661883bd2b4ef475155c7aa72b@changeid/
> >>>> This one too, at least I was not able to reproduce any fail.
> >>> Thanks for testing. I'm still not sure exactly how to reproduce your
> >>> failure, but it seems as if the root port is being allowed to suspend
> >>> before the endpoint is added to the system, and it remains so while the
> >>> endpoint is about to probe. device_initial_probe() will be OK with
> >>> respect to PM, since it will wake up the port if needed. But this
> >>> particular code is not OK, since it doesn't ensure the parent device is
> >>> active while preparing the endpoint power state.
> >>>
> >>> I suppose one way to "solve" that is (untested):
> >>>
> >>> --- a/drivers/pci/bus.c
> >>> +++ b/drivers/pci/bus.c
> >>> @@ -380,8 +380,12 @@ void pci_bus_add_device(struct pci_dev *dev)
> >>> put_device(&pdev->dev);
> >>> }
> >>>
> >>> + if (dev->dev.parent)
> >>> + pm_runtime_get_sync(dev->dev.parent);
> >>> pm_runtime_set_active(&dev->dev);
> >>> pm_runtime_enable(&dev->dev);
> >>> + if (dev->dev.parent)
> >>> + pm_runtime_put(dev->dev.parent);
> >>>
> >>> if (!dn || of_device_is_available(dn))
> >>> pci_dev_allow_binding(dev);
> >>>
> >>> Personally, I'm more inclined to go back to v1, since it prepares the
> >>> runtime PM status when the device is first discovered. That way, its
> >>> ancestors are still active, avoiding these sorts of problems. I'm
> >>> frankly not sure of all the reasons Rafael recommended I make the
> >>> v1->v3->v4 changes, and now that they cause problems, I'm inclined to
> >>> question them again.
> >>>
> >>> Rafael, do you have any thoughts?
> >> Yeah.
> >>
> >> Move back pm_runtime_set_active(&dev->dev) back to pm_runtime_init()
> > Or rather leave it there to be precise, but I think you know what I mean. :-)
> >
> >> because that would prevent the parent from suspending and keep
> >> pm_runtime_enable() here because that would prevent the device itself
> >> from suspending between pm_runtime_init() and this place.
> >>
> >> And I would add comments in both places.
>
> Confirmed, the following change (compared to $subject patch) fixed my issue:
>
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 3ef60c2fbd89..7e2b7e452d51 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -381,7 +381,6 @@ void pci_bus_add_device(struct pci_dev *dev)
> }
>
> pm_runtime_set_active(&dev->dev);
> - pm_runtime_enable(&dev->dev);

That works too, but it would defeat the purpose of the original
change, so I mean the other way around.

That is, leave the pm_runtime_enable() here and move the
pm_runtime_set_active() back to the other place.

>
> if (!dn || of_device_is_available(dn))
> pci_dev_allow_binding(dev);
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index fae5a683cf87..22b897416025 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3201,6 +3201,7 @@ void pci_pm_init(struct pci_dev *dev)
> poweron:
> pci_pm_power_up_and_verify_state(dev);
> pm_runtime_forbid(&dev->dev);
> + pm_runtime_enable(&dev->dev);
> }
>
> static unsigned long pci_ea_flags(struct pci_dev *dev, u8 prop)