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Date:   Thu, 12 Jan 2023 14:21:32 -0600
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc:     linux-pci@vger.kernel.org,
        "Limonciello, Mario" <mario.limonciello@amd.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Mehta Sanju <Sanju.Mehta@amd.com>,
        Lukas Wunner <lukas@wunner.de>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linux PM <linux-pm@vger.kernel.org>
Subject: Re: [PATCH v3] PCI / ACPI: PM: Take _S0W of the target bridge into
 account in acpi_pci_bridge_d3(()
Message-ID: <20230112202132.GA1788706@bhelgaas>
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In-Reply-To: <5659681.DvuYhMxLoT@kreacher>
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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,
> 
> 
>