linux-kernel - Re: [PATCH] PCI/pwrctrl: Skip creating platform device unless CONFIG_PCI

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Message-ID: <otrstq3g55ddtlbelzgyirpt5ahfirgkhrrietyrgbhxbueiwp@hyu4pgj6m4eo>
Date: Fri, 30 May 2025 08:46:30 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Jim Quinlan <james.quinlan@...adcom.com>
Cc: Bjorn Helgaas <helgaas@...nel.org>, Lukas Wunner <lukas@...ner.de>, 
	linux-pci@...r.kernel.org, Cyril Brulebois <kibi@...ian.org>, 
	Nicolas Saenz Julienne <nsaenz@...nel.org>, Lorenzo Pieralisi <lorenzo.pieralisi@....com>, 
	Krzysztof Wilczy??ski <kwilczynski@...nel.org>, Bartosz Golaszewski <brgl@...ev.pl>, 
	bcm-kernel-feedback-list@...adcom.com, linux-kernel@...r.kernel.org, 
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] PCI/pwrctrl: Skip creating platform device unless
 CONFIG_PCI_PWRCTL enabled

On Thu, May 29, 2025 at 03:23:29PM -0400, Jim Quinlan wrote:
> On Tue, May 27, 2025 at 6:25 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> >
> > On Sat, May 24, 2025 at 02:21:04PM +0530, Manivannan Sadhasivam wrote:
> > > On Sat, May 24, 2025 at 08:29:46AM +0200, Lukas Wunner wrote:
> > > > On Fri, May 23, 2025 at 09:42:07PM -0500, Bjorn Helgaas wrote:
> > > > > What I would prefer is something like the first paragraph in that
> > > > > section: the #ifdef in a header file that declares the function and
> > > > > defines a no-op stub, with the implementation in some pwrctrl file.
> > > >
> > > > pci_pwrctrl_create_device() is static, but it is possible to #ifdef
> > > > the whole function in the .c file and provide the stub in an #else
> > > > branch.  That's easier to follow than #ifdef'ing portions of the
> > > > function.
> > > >
> > >
> > > +1
> >
> > I dropped the ball here and didn't get any fix for this in v6.15.
> 
> :-(
> 
> >
> >
> > Why do we need pci_pwrctrl_create_device() in drivers/pci/probe.c?
> > The obvious thing would have been to put the implementation in
> > drivers/pci/pwrctrl with a stub in drivers/pci/pci.h, so I assume
> > there's some reason we can't do that?
> 
> I was wondering if we could confine PWRCTL/_SLOT to work on a per PCIe
> controller basis.  For example, if we allow the port DT node to have
> boolean "pwrctrl;" property, it would direct the PWRCTL code to
> operate on the regulators within that node.  This would allow
> CONFIG_PWRCTL/_SLOT and the pcie-brcmstb.c way of controlling
> regulators to happily coexist.
> 
> One could argue that "pwrctrl;" does not describe the HW as a DT
> property should, but I think it should be considered nevertheless.
> 

No. There were a lot of attempts previously before the advent of pwrctrl
framework to add a DT property for powering the devices, but DT maintainer
clearly said that there should be no DT property for this purpose. So we came up
with this approach.

- Mani

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