Re: [PATCH v6 1/1] PCI: Avoid putting some root ports into D3 on some Ryzen chips

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On 7/10/2023 3:33 PM, Bjorn Helgaas wrote:

It sounds like there's someplace the hardware designers specify how
this should work?  Where is that?  "Modern Standby" doesn't mean
anything to me, but maybe there's some spec that covers it?

It quickly devolves into Microsoft specific stuff though and
I can't find anything interesting to our specific issue.
Maybe this is the clue we need.  My eyes glaze over when reading that
section, but if we can come up with a commit log that starts with a
sentence from that section and connects the dots all the way to the
platform_pci_power_manageable() implementation, that might be a good
argument that 9d26d3a8f1b0 was a little too aggressive.
I like the fact that v5 ([1] for anybody following along at home) is
very generic:

   @@ bool pci_bridge_d3_possible(struct pci_dev *bridge)
   +       if (pci_pcie_type(bridge) == PCI_EXP_TYPE_ROOT_PORT &&
   +           !platform_pci_power_manageable(bridge))
   +               return false;

My objection was that we didn't have a clear connection to any specs,
so even though the code is perfectly generic, the commit log mentioned
specific cases (USB keyboard/mouse on xHCI device connected to USB-C
on AMD USB4 router).

But maybe we *could* make a convincing generic commit log.  I guess
we'd also have to explain the PCI_EXP_TYPE_ROOT_PORT part of the
OK, I'll take a stab at rewriting the v5 commit message to be more
generic as you suggested as a v7.

We might be able to drop the PCI_EXP_TYPE_ROOT_PORT part well but I
would be more worried about regressions from this.

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