linux-kernel - Re: Re: [RFC 8/9] PCI/pwrctl: add PCI power control core code

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Date: Wed, 7 Feb 2024 17:26:16 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Konrad Dybcio <konrad.dybcio@...aro.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Marcel Holtmann <marcel@...tmann.org>, Luiz Augusto von Dentz <luiz.dentz@...il.com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Alex Elder <elder@...aro.org>, Srini Kandagatla <srinivas.kandagatla@...aro.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>, 
	Abel Vesa <abel.vesa@...aro.org>, Manivannan Sadhasivam <mani@...nel.org>, Lukas Wunner <lukas@...ner.de>, 
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org, 
	linux-pci@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: Re: [RFC 8/9] PCI/pwrctl: add PCI power control core code

On Fri, Feb 2, 2024 at 5:52 PM Bjorn Andersson <andersson@...nel.org> wrote:
>
> On Fri, Feb 02, 2024 at 10:11:42AM +0100, Bartosz Golaszewski wrote:
> > On Fri, Feb 2, 2024 at 4:53 AM Bjorn Andersson <andersson@...nel.org> wrote:
> [..]
> > > > +             break;
> > > > +     }
> > > > +
> > > > +     return NOTIFY_DONE;
> > > > +}
> > > > +
> > > > +int pci_pwrctl_device_enable(struct pci_pwrctl *pwrctl)
> > >
> > > This function doesn't really "enable the device", looking at the example
> > > driver it's rather "device_enabled" than "device_enable"...
> > >
> >
> > I was also thinking about pci_pwrctl_device_ready() or
> > pci_pwrctl_device_prepared().
>
> I like both of these.
>
> I guess the bigger question is how the flow would look like in the event
> that we need to power-cycle the attached PCIe device, e.g. because
> firmware has gotten into a really bad state.
>
> Will we need an operation that removes the device first, and then cut
> the power, or do we cut the power and then call unprepared()?
>

How would the core be notified about this power-cycle from the PCI
subsystem? I honestly don't know. Is there a notifier we could
subscribe to? Is the device unbound and rebound in such case?

Bart