Message-ID: <CAJZ5v0h-f5kgJ-p4LqX_8fpz3T3AVqq_7S2n4b1vZdPQoF-MFA@mail.gmail.com>
Date: Mon, 19 Jan 2026 17:10:32 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Brian Norris <briannorris@...omium.org>, 
	Bjorn Helgaas <helgaas@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, Lukas Wunner <lukas@...ner.de>, 
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, 
	linux-pm@...r.kernel.org, Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: Re: [PATCH v4] PCI/PM: Prevent runtime suspend before devices are
 fully initialized

On Mon, Jan 19, 2026 at 2:13 PM Marek Szyprowski
<m.szyprowski@...sung.com> wrote:
>
> On 19.01.2026 13:26, Rafael J. Wysocki wrote:
> > On Mon, Jan 19, 2026 at 11:01 AM Marek Szyprowski
> > <m.szyprowski@...sung.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@...nel.org> wrote:
> >>>> On Sat, Jan 17, 2026 at 2:19 AM Brian Norris <briannorris@...omium.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.
>
> Okay, I mixed that. This way it works too and fixes the observed issue.
>
> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

Cool, thanks for verifying!

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