From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailout1.w1.samsung.com (mailout1.w1.samsung.com [210.118.77.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5DF63364026 for ; Mon, 19 Jan 2026 13:13:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=210.118.77.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768828388; cv=none; b=SCOOEF1x253DT2gUmOh4HQthMIOwgjIGbwiOq+OBso2dd+35yk1doHpErKdRvwcX0ORq36oJGGo6BnwcCejfjaiCjQyG99IZRBjw5nfej427uuLi2zjx3Z6cHWYrwcSLY8GFGPQB+l2ESJhC5ixgJCxJpJsgs85YAV8howOgewc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768828388; c=relaxed/simple; bh=k/h50n8vWqc+q0B9zN6Fs+ILbQYyrcMkfxlM47D6Gk4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:From:In-Reply-To: Content-Type:References; b=OEfUCCK5tvJ5WeGs4G1Gnprj8oWeXNjKpycLd1gs77XoJJqUtMlPgc8NrPgbgsc3isgT6Ge110UODuCpuTezxSfd4Xyt68UISkXokvUHOx4Nc8UXwwhKjU2MP3vYfxqTpkpyvRdgouxOjRXj3gwcoqt0+33TN63o31UuC8UZyxE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=samsung.com; spf=pass smtp.mailfrom=samsung.com; dkim=pass (1024-bit key) header.d=samsung.com header.i=@samsung.com header.b=b3AjMzJl; arc=none smtp.client-ip=210.118.77.11 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=samsung.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=samsung.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=samsung.com header.i=@samsung.com header.b="b3AjMzJl" Received: from eucas1p2.samsung.com (unknown [182.198.249.207]) by mailout1.w1.samsung.com (KnoxPortal) with ESMTP id 20260119131304euoutp0186be1c99c448622750bb24fdd23b926e~MJAtMUwzf0594905949euoutp01o for ; Mon, 19 Jan 2026 13:13:04 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 mailout1.w1.samsung.com 20260119131304euoutp0186be1c99c448622750bb24fdd23b926e~MJAtMUwzf0594905949euoutp01o DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=samsung.com; s=mail20170921; t=1768828384; bh=Bj9sRPcxMKBSsLFWUn5X+Cp367Ih4xF1g80Xq3QtY4E=; h=Date:Subject:To:Cc:From:In-Reply-To:References:From; b=b3AjMzJlNqVReL03wgAgp5fgYNwCUW7rqFdSOOTxXo58Orf5pGegGQPT5Ogx9dr34 bwfTyQ7iyTM6JqUepnojrRorYP4a5bEndWH8y9Wgih9NudniteO/PXe5L8uL6YBbph lYzYKhKZ0K8+t3OkbLaE/QHEsXqukt/ad6WWyWeY= Received: from eusmtip1.samsung.com (unknown [203.254.199.221]) by eucas1p1.samsung.com (KnoxPortal) with ESMTPA id 20260119131304eucas1p1d10c043c29d8fefa78dc1a3221231f27~MJAs1SWgR2584625846eucas1p1W; Mon, 19 Jan 2026 13:13:04 +0000 (GMT) Received: from [106.210.134.192] (unknown [106.210.134.192]) by eusmtip1.samsung.com (KnoxPortal) with ESMTPA id 20260119131303eusmtip15c9111c50afc306b518769c68ae4c02b~MJAsVLxov2848728487eusmtip1s; Mon, 19 Jan 2026 13:13:03 +0000 (GMT) Message-ID: <6e0c511f-1127-4a35-a40c-0161de0ec752@samsung.com> Date: Mon, 19 Jan 2026 14:13:03 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Betterbird (Windows) Subject: Re: [PATCH v4] PCI/PM: Prevent runtime suspend before devices are fully initialized To: "Rafael J. Wysocki" Cc: Brian Norris , Bjorn Helgaas , Bjorn Helgaas , Lukas Wunner , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-pm@vger.kernel.org, =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= Content-Language: en-US From: Marek Szyprowski In-Reply-To: Content-Transfer-Encoding: 8bit X-CMS-MailID: 20260119131304eucas1p1d10c043c29d8fefa78dc1a3221231f27 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20260114094643eucas1p1a2fdc6c35dd27741c18831b34bbed0c8 X-EPHeader: CA X-CMS-RootMailID: 20260114094643eucas1p1a2fdc6c35dd27741c18831b34bbed0c8 References: <20260106222715.GA381397@bhelgaas> <0e35a4e1-894a-47c1-9528-fc5ffbafd9e2@samsung.com> <61e8c93c-d096-4807-b2dd-a22657f2e06a@samsung.com> On 19.01.2026 13:26, Rafael J. Wysocki wrote: > On Mon, Jan 19, 2026 at 11:01 AM Marek Szyprowski > wrote: >> On 18.01.2026 12:59, Rafael J. Wysocki wrote: >>> On Sun, Jan 18, 2026 at 12:53 PM Rafael J. Wysocki wrote: >>>> On Sat, Jan 17, 2026 at 2:19 AM Brian Norris 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 Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland