linux-kernel - Re: [PATCH v5 3/4] PCI: Decouple D3Hot and D3Cold handling for bridges

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Message-ID: <20240829061003.v2oghhp6buncosdo@thinkpad>
Date: Thu, 29 Aug 2024 11:40:03 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Oliver Neukum <oneukum@...e.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	lukas@...ner.de, mika.westerberg@...ux.intel.com,
	Hsin-Yi Wang <hsinyi@...omium.org>
Subject: Re: [PATCH v5 3/4] PCI: Decouple D3Hot and D3Cold handling for
 bridges

On Tue, Aug 20, 2024 at 06:45:04PM -0500, Bjorn Helgaas wrote:
> On Tue, Aug 20, 2024 at 11:30:08AM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Aug 19, 2024 at 02:44:43PM +0200, Oliver Neukum wrote:
> > > On 02.08.24 07:55, Manivannan Sadhasivam via B4 Relay wrote:
> > > 
> > > > --- a/drivers/pci/pci-acpi.c
> > > > +++ b/drivers/pci/pci-acpi.c
> > > > @@ -1434,7 +1434,7 @@ void pci_acpi_setup(struct device *dev, struct acpi_device *adev)
> > > >   	 * reason is that the bridge may have additional methods such as
> > > >   	 * _DSW that need to be called.
> > > >   	 */
> > > > -	if (pci_dev->bridge_d3_allowed)
> > > > +	if (pci_dev->bridge_d3cold_allowed && pci_dev->bridge_d3hot_allowed)
> > > 
> > > Are you sure you want to require both capabilities here?
> > 
> > Wakeup is common for both D3Hot and D3Cold, isn't it?
> 
> From a spec point of view, moving device from D3hot to D0 is a config
> space write that the OS knows how to do, but moving a device from
> D3cold to D0 requires some platform-specific magic.  If that's what
> you mean by wakeup, they don't look common to me.
> 

I agree that the wakeup mechanism differs between D3hot and D3cold, but I'm not
sure about enabling the wakeup capability of the bridge if only one (D3hot or
D3cold) is allowed. So I went with the requirement of having both. Otherwise,
how can we differentiate wakeup from D3hot vs wakeup from D3cold?

- Mani

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