Re: [PATCH V13 02/12] PCI: host-generic: Add common helpers for parsing Root Port properties

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Apr 17, 2026 at 03:17:16AM +0000, Sherry Sun wrote:
> > On Thu, Apr 16, 2026 at 07:14:12PM +0800, Sherry Sun wrote:
> > > Introduce generic helper functions to parse Root Port device
> > > tree nodes and extract common properties like reset GPIOs. This
> > > allows multiple PCI host controller drivers to share the same
> > > parsing logic.
> > >
> > > Define struct pci_host_port to hold common Root Port properties
> > > (currently only reset GPIO descriptor) and add
> > > pci_host_common_parse_ports() to parse Root Port nodes from
> > > device tree.
> > 
> > Are the Root Port and the RC the only possible places for 'reset'
> > GPIO descriptions in DT?  I think PERST# routing is outside the
> > PCIe spec, so it seems like a system could provide a PERST# GPIO
> > routed to any Switch Upstream Port or Endpoint (I assume a PERST#
> > connected to a switch would apply to both the upstream port and
> > the downstream ports).
> 
> Thanks for the feedback. You're right that PERST# routing could
> theoretically be connected to any device in the hierarchy. However,
> for this patch series, I've focused on the most common use case in
> practice: use Root Port level PERST# instead of the legacy Root
> Complex level PERST#.
> 
> Root Port level PERST# - This is the primary target, where each Root
> Port has individual control over devices connected to it.  RC level
> PERST# - Legacy binding support, where a single GPIO controls all
> ports.
> 
> We can extend this framework later if real hardware emerges that
> needs Switch or EP-level PERST# control. I can add a comment
> documenting this limitation if needed.
> 
> BTW, Mani and Rob had some great discussions in dt-schema about
> PERST# and WAKE# sideband signals settings.

> You can check here:
> https://github.com/devicetree-org/dt-schema/issues/168
> https://github.com/devicetree-org/dt-schema/pull/126
> https://github.com/devicetree-org/dt-schema/pull/170

The upshot of all those conversations is that WAKE# and PERST# can be
routed to arbitrary devices independent of the PCI topology.

I think extending host-generic to look for 'reset' in Root Port nodes
is the right thing.  My concern is more about where we store it.  This
patch saves it in a new "pci_host_port" struct, but someday we'll want
a place to save the PERST# GPIOs for several slots behind a switch.
Then we'll have two different ways to save the same information.

WAKE# signals might be more pertinent -- we definitely need to support
multiple WAKE# signals below a single Root Port, and it seems like
PERST# and WAKE# GPIOs should be saved the same place.

I'm wondering if both should go in the pci_dev itself.  I guess the
implication is that a pci_dev->reset GPIO would describe a PERST#
connected to the device *below* the pci_dev, at least for Downstream
Ports.

I don't know about WAKE# signals.  When it's in a connector, there's
probably only a single possible WAKE# per Downstream Port.  But is it
possible have multiple WAKE# signals from a multi-function device
that's on the motherboard?  Saving the WAKE# GPIO in the Downstream
Port wouldn't accommodate that case.