linux-kernel - Re: [PATCH v3 1/2] PCI: don't rely on of_platform

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Message-ID: <CAMRc=Mfd08i0NFsuf=igJRJszDNfLyHf+bf6ExjNYxX41CMdWA@mail.gmail.com>
Date: Tue, 27 Aug 2024 14:25:58 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Krishna chaitanya chundru <quic_krichai@...cinc.com>, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 1/2] PCI: don't rely on of_platform_depopulate() for
 reused OF-nodes

On Tue, Aug 27, 2024 at 10:40 AM Manivannan Sadhasivam
<manivannan.sadhasivam@...aro.org> wrote:
>
> + Rob
>
> On Fri, Aug 23, 2024 at 11:33:22AM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > of_platform_depopulate() doesn't play nice with reused OF nodes - it
> > ignores the ones that are not marked explicitly as populated and it may
> > happen that the PCI device goes away before the platform device in which
> > case the PCI core clears the OF_POPULATED bit. We need to
> > unconditionally unregister the platform devices for child nodes when
> > stopping the PCI device.
> >
>
> It sounds like the fix is in of_platform_depopulate() itself and this patch
> works around the API issue in PCI driver.
>
> Rob, is that correct?
>
> - Mani

of_platform_depopulate() has more issues than just that. For one: it's
asymmetric to of_platform_populate() as it takes a struct device as
argument and not a device node. This causes issues for users like TI
aemif that call of_platform_populate() on nodes without the compatible
property that are never consumed by any device. AFAIK there's
currently no way to depopulate them.

In this particular case I think that the OF_POPULATED bit should not
be set when the PCI device is created but only when the platform
device is.

However I'm afraid to change the semantics of of_platform_depopulate()
et al for all users so I'm more inclined to have this fix in v6.11 to
avoid releasing non functional code (pwrctl devices not being removed)
and then possibly introduce a new variant of of_platform_depopulate()
that would work slightly differently.

Bart