RE: [PATCH v4] PCI / ACPI: PM: Take _S0W of the target bridge into account in acpi_pci_bridge_d3(()

[Limonciello, Mario]

[AMD Official Use Only - General]



> -----Original Message-----
> From: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> Sent: Thursday, January 12, 2023 16:41
> To: Limonciello, Mario <Mario.Limonciello@xxxxxxx>
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>; linux-pci@xxxxxxxxxxxxxxx; Rafael J.
> Wysocki <rafael@xxxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; Bjorn Helgaas
> <bhelgaas@xxxxxxxxxx>; Mika Westerberg
> <mika.westerberg@xxxxxxxxxxxxxxx>; Mehta, Sanju <Sanju.Mehta@xxxxxxx>;
> Lukas Wunner <lukas@xxxxxxxxx>; Rafael J . Wysocki
> <rafael.j.wysocki@xxxxxxxxx>; linux-acpi@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Linux PM <linux-pm@xxxxxxxxxxxxxxx>
> Subject: Re: [PATCH v4] PCI / ACPI: PM: Take _S0W of the target bridge into
> account in acpi_pci_bridge_d3(()
> 
> On Thu, Jan 12, 2023 at 10:09:21PM +0000, Limonciello, Mario wrote:
> > > -----Original Message-----
> > > From: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> > > Sent: Thursday, January 12, 2023 16:02
> > > To: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> > > Cc: linux-pci@xxxxxxxxxxxxxxx; Limonciello, Mario
> > > <Mario.Limonciello@xxxxxxx>; Rafael J. Wysocki <rafael@xxxxxxxxxx>;
> Len
> > > Brown <lenb@xxxxxxxxxx>; Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; Mika
> > > Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>; Mehta, Sanju
> > > <Sanju.Mehta@xxxxxxx>; Lukas Wunner <lukas@xxxxxxxxx>; Rafael J .
> > > Wysocki <rafael.j.wysocki@xxxxxxxxx>; linux-acpi@xxxxxxxxxxxxxxx; linux-
> > > kernel@xxxxxxxxxxxxxxx; Linux PM <linux-pm@xxxxxxxxxxxxxxx>
> > > Subject: Re: [PATCH v4] PCI / ACPI: PM: Take _S0W of the target bridge into
> > > account in acpi_pci_bridge_d3(()
> > >
> > > On Thu, Jan 12, 2023 at 09:51:24PM +0100, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > > >
> > > > It is generally questionable to allow a PCI bridge to go into D3 if
> > > > it has _S0W returning D2 or a shallower power state, so modify
> > > > acpi_pci_bridge_d3(() to always take the return value of _S0W for the
> > > > target bridge into accout.  That is, make it return 'false' if _S0W
> > > > returns D2 or a shallower power state for the target bridge regardless
> > > > of its ancestor PCIe Root Port properties.  Of course, this also causes
> > > > 'false' to be returned if the PCIe Root Port itself is the target and
> > > > its _S0W returns D2 or a shallower power state.
> > > >
> > > > However, still allow bridges without _S0W that are power-manageable via
> > > > ACPI to enter D3 to retain the current code behavior in that case.
> > > >
> > > > Link: https://lore.kernel.org/linux-pci/20221031223356.32570-1-
> > > mario.limonciello@xxxxxxx/
> > > > Reported-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > >
> > > Applied to pci/pm for v6.3, thanks!
> > >
> > > It'd be great if we could include a short description of the problems
> > > users might see.  I think the original problem was that on some AMD
> > > systems we put a USB4 router in D3 when it should remain in D0.  And I
> > > assume this means something doesn't wake up when it should?  Or maybe
> > > we miss a hotplug event?
> > >
> > > If somebody has an example or some text, I'll add it to the commit
> > > log.
> >
> > Here's a blurb for what happens on AMD side:
> >
> > When the platform is configured to not allow the PCIe port used for
> > tunneling to wakeup from D3 it will runtime suspend into D0 and the
> > USB4 controller which is a consumer will runtime suspend into D3.
> >
> > This inconsistency leads to failures to initialize PCIe tunnels for
> > USB4 devices.
> 
> And what is J. Random User going to see?  DisplayPort not working
> ever?  It works to begin with, but not after a suspend?  Devices in a
> dock not being able to wake the system?
> 
> I don't really know what "PCIe tunnels for USB4 devices not being
> initialized" means for me.  I want to know what a problem report from
> a non-expert user might look like.
> 

DP tunnels aren't affected, so monitors should still work.

In terms of what doesn't work it depends on the architecture of the
the connected device.  Here's some concrete up-leveled examples:

USB4 docks contain that a PCIe network adapter and that adapter won't
work when the dock is plugged in after the system boot.

USB4 docks that contain a USB network adapter should work properly,
but downstream USB4 or TBT3 devices connected to that USB4 dock will
not work when the device or dock is plugged in after the system boots.

TBT3 storage devices connected after the system has booted will not work.

Thanks,