Re: [PATCH v3] PCI / ACPI: PM: Take _S0W of the target bridge into account in acpi_pci_bridge_d3(()

Rafael J. Wysocki
2023-01-12T20:55:22Z

On Thu, Jan 12, 2023 at 9:21 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Wed, Jan 11, 2023 at 11:38:55AM +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > 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@amd.com/
> > Reported-by: Mario Limonciello <mario.limonciello@amd.com>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >
> > v2 -> v3:
> > * Use rpadev for the ACPI companion of the Root Port in acpi_pci_bridge_d3(()
> > to avoid confusion.
> > * Make the function evaluating _S0W return the value produced by it or "unknown
> > state" on errors and let its caller deal with that value.
> >
> > ---
> > drivers/acpi/device_pm.c | 19 +++++++++++++++++++
> > drivers/pci/pci-acpi.c | 45 +++++++++++++++++++++++++++++++--------------
> > include/acpi/acpi_bus.h | 1 +
> > 3 files changed, 51 insertions(+), 14 deletions(-)
> >
> > Index: linux-pm/drivers/pci/pci-acpi.c
> > ===================================================================
> > --- linux-pm.orig/drivers/pci/pci-acpi.c
> > +++ linux-pm/drivers/pci/pci-acpi.c
> > @@ -976,24 +976,41 @@ bool acpi_pci_power_manageable(struct pc
> > bool acpi_pci_bridge_d3(struct pci_dev *dev)
> > {
> > struct pci_dev *rpdev;
> > - struct acpi_device *adev;
> > - acpi_status status;
> > - unsigned long long state;
> > + struct acpi_device *adev, *rpadev;
> > const union acpi_object *obj;
> >
> > if (acpi_pci_disabled || !dev->is_hotplug_bridge)
> > return false;
> >
> > - /* Assume D3 support if the bridge is power-manageable by ACPI. */
> > - if (acpi_pci_power_manageable(dev))
> > - return true;
> > + adev = ACPI_COMPANION(&dev->dev);
> > + if (adev) {
> > + /*
> > + * If the bridge has _S0W, whether or not it can go into D3
> > + * depends on what is returned by that object. In particular,
> > + * if the power state returned by _S0W is D2 or shallower,
> > + * entering D3 should not be allowed.
> > + */
> > + if (acpi_dev_power_state_for_wake(adev) <= ACPI_STATE_D3_HOT)
>
> The comment suggests that this should check for "<= ACPI_STATE_D2"
> (not ACPI_STATE_D3_HOT). Or is there some subtlety here that I'm
> missing?

No, this is a mistake. I'll send a v4.