Re: [PATCH v13 01/12] PCI: Only put Intel PCIe ports >= 2015 into D3

[Rafael J. Wysocki]

On Fri, Aug 18, 2023 at 10:21 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> From: Rafael J. Wysocki
> > Sent: Friday, August 18, 2023 9:12 AM
> >
> > On Fri, Aug 18, 2023 at 7:14 AM Mario Limonciello
> > <mario.limonciello@xxxxxxx> wrote:
> > >
> > > commit 9d26d3a8f1b0 ("PCI: Put PCIe ports into D3 during suspend")
> > > changed pci_bridge_d3_possible() so that any vendor's PCIe ports
> > > from modern machines (>=2015) are allowed to be put into D3.
> > >
> > > Iain reports that USB devices can't be used to wake a Lenovo Z13
> > > from suspend. This is because the PCIe root port has been put
> > > into D3 and AMD's platform can't handle USB devices waking in this
> > > case.
> > >
> ...
> > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > > index 60230da957e0c..051e88ee64c63 100644
> > > --- a/drivers/pci/pci.c
> > > +++ b/drivers/pci/pci.c
> > > @@ -3037,10 +3037,11 @@ bool pci_bridge_d3_possible(struct pci_dev *bridge)
> > >                         return false;
> > >
> > >                 /*
> > > -                * It should be safe to put PCIe ports from 2015 or newer
> > > +                * It is safe to put Intel PCIe ports from 2015 or newer
> > >                  * to D3.
> > >                  */
> >
> > I would say "Allow Intel PCIe ports from 2015 onward to go into D3 to
> > achieve additional energy conservation on some platforms" without the
> > "It is safe" part that is kind of obvious (it wouldn't be done if it
> > were unsafe).
>
> Just say why...
>
> "Don't put root ports into D3 on non-Intel systems to avoid issues
> with USB devices being unable to wake up some AMD based laptops."

Well, both pieces of information are actually useful: Why it is done
on Intel systems in the first place and why it cannot be done on AMD
systems.