Message-ID: <d2c006c3-44c3-4270-b1ca-5d1a0d7f4e09@samsung.com>
Date: Mon, 19 Jan 2026 11:00:55 +0100
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>, Brian Norris
	<briannorris@...omium.org>
Cc: 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 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);

         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)


Feel free to add:

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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