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

Bjorn Helgaas
2023-01-12T20:51:03Z

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?

> + return false;
> +
> + /*
> + * Otherwise, assume that the bridge can enter D3 so long as it
> + * is power-manageable via ACPI.
> + */
> + if (acpi_device_power_manageable(adev))
> + return true;
> + }
>
> rpdev = pcie_find_root_port(dev);
> if (!rpdev)
> return false;
>
> - adev = ACPI_COMPANION(&rpdev->dev);
> - if (!adev)
> + if (rpdev == dev)
> + rpadev = adev;
> + else
> + rpadev = ACPI_COMPANION(&rpdev->dev);
> +
> + if (!rpadev)
> return false;
>
> /*
> @@ -1001,15 +1018,15 @@ bool acpi_pci_bridge_d3(struct pci_dev *
> * doesn't supply a wakeup GPE via _PRW, it cannot signal hotplug
> * events from low-power states including D3hot and D3cold.
> */
> - if (!adev->wakeup.flags.valid)
> + if (!rpadev->wakeup.flags.valid)
> return false;
>
> /*
> - * If the Root Port cannot wake itself from D3hot or D3cold, we
> - * can't use D3.
> + * In the bridge-below-a-Root-Port case, evaluate _S0W for the Root Port
> + * to verify whether or not it can signal wakeup from D3.
> */
> - status = acpi_evaluate_integer(adev->handle, "_S0W", NULL, &state);
> - if (ACPI_SUCCESS(status) && state < ACPI_STATE_D3_HOT)
> + if (rpadev != adev &&
> + acpi_dev_power_state_for_wake(rpadev) <= ACPI_STATE_D3_HOT)

Same question here.

> return false;
>
> /*
> @@ -1018,7 +1035,7 @@ bool acpi_pci_bridge_d3(struct pci_dev *
> * bridges *below* that Root Port can also signal hotplug events
> * while in D3.
> */
> - if (!acpi_dev_get_property(adev, "HotPlugSupportInD3",
> + if (!acpi_dev_get_property(rpadev, "HotPlugSupportInD3",
> ACPI_TYPE_INTEGER, &obj) &&
> obj->integer.value == 1)
> return true;
> Index: linux-pm/drivers/acpi/device_pm.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/device_pm.c
> +++ linux-pm/drivers/acpi/device_pm.c
> @@ -484,6 +484,25 @@ void acpi_dev_power_up_children_with_adr
> acpi_dev_for_each_child(adev, acpi_power_up_if_adr_present, NULL);
> }
>
> +/**
> + * acpi_dev_power_state_for_wake - Deepest power state for wakeup signaling
> + * @adev: ACPI companion of the target device.
> + *
> + * Evaluate _S0W for @adev and return the value produced by it or return
> + * ACPI_STATE_UNKNOWN on errors (including _S0W not present).
> + */
> +u8 acpi_dev_power_state_for_wake(struct acpi_device *adev)
> +{
> + unsigned long long state;
> + acpi_status status;
> +
> + status = acpi_evaluate_integer(adev->handle, "_S0W", NULL, &state);
> + if (ACPI_FAILURE(status))
> + return ACPI_STATE_UNKNOWN;
> +
> + return state;
> +}
> +
> #ifdef CONFIG_PM
> static DEFINE_MUTEX(acpi_pm_notifier_lock);
> static DEFINE_MUTEX(acpi_pm_notifier_install_lock);
> Index: linux-pm/include/acpi/acpi_bus.h
> ===================================================================
> --- linux-pm.orig/include/acpi/acpi_bus.h
> +++ linux-pm/include/acpi/acpi_bus.h
> @@ -533,6 +533,7 @@ int acpi_bus_update_power(acpi_handle ha
> int acpi_device_update_power(struct acpi_device *device, int *state_p);
> bool acpi_bus_power_manageable(acpi_handle handle);
> void acpi_dev_power_up_children_with_adr(struct acpi_device *adev);
> +u8 acpi_dev_power_state_for_wake(struct acpi_device *adev);
> int acpi_device_power_add_dependent(struct acpi_device *adev,
> struct device *dev);
> void acpi_device_power_remove_dependent(struct acpi_device *adev,
>
>
>