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

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Date: Thu, 8 Feb 2024 17:02:01 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Bartosz Golaszewski <brgl@...ev.pl>,
	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 02, 2024 at 10:52:11AM -0600, Bjorn Andersson 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()?
> 

Currently, we don't power cycle while resetting the devices. Most of the drivers
just do a software reset using some register writes. Part of the reason for
that is, the drivers themselves don't control the power to the devices and there
would be no way to let the parent know about the firmware crash.

- Mani

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