Re: [PATCH v21] PCI: Avoid D3 at suspend for AMD PCIe root ports w/ USB4 controllers

[Lukas Wunner <lukas@wunner.de>]

On Tue, Oct 03, 2023 at 03:16:47PM -0500, Mario Limonciello wrote:
> On 10/3/2023 15:00, Lukas Wunner wrote:
> > The pcie_find_root_port() function you're
> > using here will walk up the hierarchy until it finds the Root Port,
> > i.e. it's specifically for the case where there are switches between
> > the USB controller and Root Port (which I think you want to exclude).
> > I would have expected that you just call pci_upstream_bridge(dev) once
> > and check whether the returned device is a PCI_EXP_TYPE_ROOT_PORT.
> > 
> 
> Is there an advantage to using pci_upstream_bridge() given it's just one
> step up with pcie_find_root_port()?

Not really, no.  The information I was missing is that these Device IDs
are unique to the SoC and will never appear in a Thunderbolt-attached
device.

> That's exactly what I was worried about - what if other callers end up using
> pci_d3cold_disable/pci_d3cold_enable for some reason. We're all fighting for
> the same policy bits.
> 
> This being said, I am tending to agree with Bjorn, it's better to just clear
> the PME bits.

Fair enough, I'm sorry I led you down the wrong path with that
suggestion.  I guess no_d3cold is generally only useful for the
"D3cold is known to be broken *permanently*" use case.  Incidentally,
there's only a single driver in the tree calling pci_d3cold_enable()
and that's i915.  And it likewise disables and re-enables the flag at
the Root Port, just like you did.

Thanks,

Lukas