linux-kernel - Re: [PATCH v5] PCI/ACPI: PCI/ACPI: Validate devices with power resources support D3

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Date:   Mon, 14 Nov 2022 16:33:52 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     "Limonciello, Mario" <mario.limonciello@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Mehta Sanju <Sanju.Mehta@....com>,
        Lukas Wunner <lukas@...ner.de>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] PCI/ACPI: PCI/ACPI: Validate devices with power
 resources support D3

On Fri, Nov 11, 2022 at 10:42 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Fri, Nov 11, 2022 at 12:58:28PM -0600, Limonciello, Mario wrote:
> > On 11/11/2022 11:41, Bjorn Helgaas wrote:
> > > On Mon, Oct 31, 2022 at 05:33:55PM -0500, Mario Limonciello wrote:
> > > > Firmware typically advertises that ACPI devices that represent PCIe
> > > > devices can support D3 by a combination of the value returned by
> > > > _S0W as well as the HotPlugSupportInD3 _DSD [1].
> > > >
> > > > `acpi_pci_bridge_d3` looks for this combination but also contains
> > > > an assumption that if an ACPI device contains power resources the PCIe
> > > > device it's associated with can support D3.  This was introduced
> > > > from commit c6e331312ebf ("PCI/ACPI: Whitelist hotplug ports for
> > > > D3 if power managed by ACPI").
> > > >
> > > > Some firmware configurations for "AMD Pink Sardine" do not support
> > > > wake from D3 in _S0W for the ACPI device representing the PCIe root
> > > > port used for tunneling. The PCIe device will still be opted into
> > > > runtime PM in the kernel [2] because of the logic within
> > > > `acpi_pci_bridge_d3`. This currently happens because the ACPI
> > > > device contains power resources.
>
> Wait.  Is this as simple as just recognizing that:
>
>   _PS0 means the OS has a knob to put the device in D0, but it doesn't
>   mean the device can wake itself from a low-power state.  The OS has
>   to use _S0W to learn the device's ability to wake itself.

It is.

> If that's enough, maybe we don't need to complicate this with all the
> Thunderbolt and device link stuff.  Which would be great, because the
> code change itself has nothing to do with those things.

Indeed.