Re: [PATCH v18 2/2] PCI: Add a quirk for AMD PCIe root ports w/ USB4 controllers

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On Wed, Sep 13, 2023 at 6:35 PM Mario Limonciello
<mario.limonciello@xxxxxxx> wrote:
> On 9/13/2023 10:40, Bjorn Helgaas wrote:
> > On Wed, Sep 13, 2023 at 12:20:14PM +0200, Rafael J. Wysocki wrote:
> >> On Wed, Sep 13, 2023 at 6:11 AM Mario Limonciello
> >> <mario.limonciello@xxxxxxx> wrote:


> >
> > Also, do we have some indication that this is specific to Ryzen?  If
> > not, I assume this is an ongoing issue, and matching on Device IDs
> > just means we'll have to debug the same problem again and add more
> > IDs.
> This is why my earlier attempts (v16 and v17) tried to tie it to
> constraints.  These are what the uPEP driver in Windows uses to make the
> decision of what power state to put integrated devices like the root
> port into.
> In Windows if no uPEP driver is installed "Windows internal policy"
> dictates what happens.  If the uPEP driver is installed then it
> influences the policy based upon the constraints.
> Rafael had feedback against constraints in v17, which is why I'm back to
> a quirk for v18.
> This issue as I've described it is specific to AMD Ryzen.

OK, so a quirk is the way to go IMO, because starting to rely on LPI
constraints in general retroactively is almost guaranteed to regress
things this way or another.

Whatever is done, it needs to be Ryzen-specific, unless there is
evidence that other (and in particular non-AMD) platforms are

> I expect it to be an ongoing issue.  I also expect unless we use
> constraints or convince the firmware team to add a _S0W object with a
> value of "0" for the sake of Linux that we will be adding IDs every year
> to wherever this lands as we reproduce it on newer SoCs.

So maybe the way to go is to make the AMD PMC driver set a flag for
Root Ports on suspend or similar.

In any case, I think that it would be good to agree on the approach at
the general level before posting any new patches, because we seem to
be going back and forth here.

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