linux-kernel - Re: [PATCH 6.13] PCI/pwrctrl: Skip NULL of

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Message-ID: <20241209174620.6a53t5k2qgmgleix@thinkpad>
Date: Mon, 9 Dec 2024 23:16:20 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Lukas Wunner <lukas@...ner.de>
Cc: Bjorn Helgaas <helgaas@...nel.org>,
	Brian Norris <briannorris@...omium.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Wilczy??ski <kwilczynski@...nel.org>,
	Krishna chaitanya chundru <quic_krichai@...cinc.com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Jon Hunter <jonathanh@...dia.com>,
	Saurabh Sengar <ssengar@...ux.microsoft.com>
Subject: Re: [PATCH 6.13] PCI/pwrctrl: Skip NULL of_node when unregistering

On Sun, Dec 01, 2024 at 11:54:45AM +0100, Lukas Wunner wrote:
> On Sun, Dec 01, 2024 at 01:51:08PM +0530, Manivannan Sadhasivam wrote:
> > The idea of pci_pwrctrl_unregister() is to remove the pwrctl device when the
> > associated PCI device gets removed. When this happens, the pwrctl driver will
> > turn off the power to the corresponding PCI device
> 
> After pci_pwrctrl_unregister() is called from pci_stop_dev(),
> the device may be accessed by one of the calls in pci_destroy_dev().
> 
> E.g. pci_doe_destroy() may set the DOE Abort bit in the DOE Control
> Register if a DOE exchange is ongoing.  One cannot assume that no
> such exchange is ongoing merely because the device was unbound from
> its driver.  The PCI core may have legitimate reasons to perform a DOE
> exchange or generally access config space even after the device has been
> unbound.  And IIUC, those accesses will fail if pwrctrl has powered the
> device down.
> 
> Another example is pcie_aspm_exit_link_state(), which will adjust ASPM
> settings on device removal.
> 
> So it seems to me that the call to pci_pwrctrl_unregister() needs to be
> moved to pci_doe_destroy().  However I'm worried that will break the
> symmetry with pci_pwrctrl_create_devices(), which is only called in the
> !pci_dev_is_added() case.
> 

So I took a stab at both of your suggestions:

1. Moving the pwrctrl devices creation to pci_scan_device()
2. Moving the pwrctrl devices unregister to pci_destroy_dev()

Both seems to be working fine and it also allows creating pwrctrl devices for
the PCI bridges without any change (for which I was planning to add one more
patch earlier). But the devlink creation still needs to happen in
pci_bus_add_device(), which I think is fine.

Will post the patches tomorrow, thanks!

- Mani

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