[PATCH v5 1/5] PCI: host-common: Add helper to determine host bridge D3cold eligibility

[Manivannan Sadhasivam]

On Wed, May 20, 2026 at 03:27:55PM -0500, Bjorn Helgaas wrote:
> On Tue, May 19, 2026 at 05:39:01PM -0500, Bjorn Helgaas wrote:
> > On Wed, Apr 29, 2026 at 12:12:23PM +0530, Krishna Chaitanya Chundru wrote:
> > > Add a common helper, pci_host_common_d3cold_possible(), to determine
> > > whether PCIe devices under host bridge can safely transition to D3cold.
> > ...
> 
> > > +static int __pci_host_common_d3cold_possible(struct pci_dev *pdev, void *userdata)
> > > +{
> > > +	u32 *flags = userdata;
> > > +	int type;
> > > +
> > > +	/* Ignore conventional PCI devices */
> > > +	if (!pci_is_pcie(pdev))
> > > +		return 0;
> > > +
> > > +	type = pci_pcie_type(pdev);
> > > +	if (type != PCI_EXP_TYPE_ENDPOINT &&
> > > +	    type != PCI_EXP_TYPE_LEG_END &&
> > > +	    type != PCI_EXP_TYPE_RC_END)
> > > +		return 0;
> > 
> > From https://sashiko.dev/#/patchset/20260429-d3cold-v5-0-89e9735b9df6%40oss.qualcomm.com:
> > 
> >   If the topology contains an active conventional PCI device or an
> >   intermediate PCIe switch in PCI_D0, returning 0 here allows
> >   pci_walk_bus() to continue without clearing the
> >   PCI_HOST_D3COLD_ALLOWED flag.
> > 
> >   Does this create a situation where the host bridge might
> >   aggressively power off the link, dropping power to these active
> >   components?
> > 
> > I guess this is intentional, since you have comment about ignoring
> > conventional PCI devices.  But this does seem like a potential
> > problem.  Why should we ignore switches here?  And I think it's still
> > fairly common to have a PCIe-to-PCI bridge leading to a conventional
> > PCI device, and I don't know why we should ignore them.
> > 
> > The commit log consistently refers to "PCIe" devices and endpoints, so
> > maybe there's some reason that I'm missing.
> > 
> > There are other sashiko comments on this series that I think should
> > also be looked at.
> 
> This series is all in pci/next, so you and Mani can decide on whether
> any sashiko comments need to be addressed.
> 
> Even if there's no code change, I think it'd be nice to have a brief
> comment here about why conventional PCI and switches are ignored.

Looking at the helper again, I think we should allow all PCI/PCIe devices to
take part in the D3Cold check including Switch, Bridge, RP, RCiEP and RC-EC.
Some of them like RCiEP and RC-EC cannot be put into D3Cold by the host
controller drivers individually, but if they are bound to a driver, then there
is a possibility that the driver would want those devices to be kept in D0 for
some reason. In that case, the host controller driver should not broadcast
PME_Turn_Off.

So I've removed the PCIe device checks altogether including the check for
conventional PCI devices in the PCI tree.

- Mani

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