linux-kernel - Re: [PATCH v5 1/4] PCI/portdrv: Make use of pci_dev::bridge

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Message-ID: <Zq08i2i_ETHsJiKW@wunner.de>
Date: Fri, 2 Aug 2024 22:07:39 +0200
From: Lukas Wunner <lukas@...ner.de>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: manivannan.sadhasivam@...aro.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Len Brown <lenb@...nel.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	mika.westerberg@...ux.intel.com, Hsin-Yi Wang <hsinyi@...omium.org>
Subject: Re: [PATCH v5 1/4] PCI/portdrv: Make use of pci_dev::bridge_d3 for
 checking the D3 possibility

On Fri, Aug 02, 2024 at 01:19:24PM +0200, Rafael J. Wysocki wrote:
> On Fri, Aug 2, 2024 at 11:49AM Lukas Wunner <lukas@...ner.de> wrote:
> >
> > On Fri, Aug 02, 2024 at 11:25:00AM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> > > PCI core is already caching the value of pci_bridge_d3_possible() in
> > > pci_dev::bridge_d3 during pci_pm_init(). Since the value is not going to
> > > change,
> 
> Is that really the case?
> 
> Have you seen pci_bridge_d3_update()?

Okay the value may change at runtime, e.g. due to user space
manipulating d3cold_allowed in sysfs.

> > I don't know if there was a reason to call pci_bridge_d3_possible()
> > (instead of using the cached value) on probe, remove and shutdown.
> >
> > The change is probably safe but it would still be good to get some
> > positive test results with Thunderbolt laptops etc to raise the
> > confidence.
> 
> If I'm not mistaken, the change is not correct.

You're right.  Because the value may change, different code paths
may be chosen on probe, remove and shutdown.  Sorry for missing that.

Thanks,

Lukas