Re: [PATCH 1/4] PCI: Introduce an API to check if RC/platform can retain device context during suspend

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Apr 17, 2026 at 04:41:09PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Apr 16, 2026 at 02:18:55PM -0500, Bjorn Helgaas wrote:
> > On Tue, Apr 14, 2026 at 09:29:39PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> > > From: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
> > > 
> > > Currently, the PCI endpoint drivers like NVMe checks whether the device
> > > context will be retained or not during system suspend, with the help of
> > > pm_suspend_via_firmware() API.
> > > 
> > > But it is possible that the device context might be lost due to some
> > > platform limitation as well. Having those checks in the endpoint drivers
> > > will not scale and will cause a lot of code duplication.
> ...

> > > + * pci_dev_suspend_retention_supported - Check if the platform can retain the device
> > > + *					 context during system suspend
> > > + * @pdev: PCI device to check
> > > + *
> > > + * Returns true if the platform can guarantee to retain the device context,
> > > + * false otherwise.
> > > + */
> > > +bool pci_dev_suspend_retention_supported(struct pci_dev *pdev)
> > 
> > This doesn't seem like the right name.  This isn't a property of the
> > *device*; that's all determined by the PCI spec (devices must retain
> > all internal state in D0, D1, and D2, they retain it in D3hot if
> > No_Soft_Reset, and they never do in D3cold).
> > 
> > So this seems like something to do with the *platform* behavior.  It
> > sounds like this is basically a way to learn whether the device might
> > be put in D3cold on system suspend.
> 
> That's correct. But I wanted to keep it device specific, since apart
> from pm_suspend_via_firmware() there could be other issues causing
> context to be lost. Like the issue with RC, brought up in the
> successive patches. There could be chances that only one hierarchy
> might be affected. So making it device specific would give us the
> granularity.

OK, a device-specific API is fine.

Maybe it could be something like "pci_suspend_preserves_context()"?

Is it the case that suspend never uses D3cold?  If suspend ever uses
D3cold, *every* device put in D3cold will lose its context.

How would this work if suspend can use D3cold?  Can a driver (or this
API) learn whether D3cold might be used?