Message-ID: <f25d3b59-92c5-342c-ceb8-7feed76ce77f@amd.com>
Date:   Tue, 3 Jan 2023 16:44:22 -0600
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     "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 1/2/2023 10:59, Rafael J. Wysocki wrote:
> On Monday, January 2, 2023 5:34:19 PM CET Rafael J. Wysocki wrote:
>> On Monday, November 21, 2022 11:17:42 PM CET Bjorn Helgaas wrote:
>>> On Mon, Nov 21, 2022 at 03:33:00PM +0100, Rafael J. Wysocki wrote:
>>>> On Friday, November 18, 2022 10:13:39 PM CET Rafael J. Wysocki wrote:
>>>>> On Fri, Nov 18, 2022 at 9:23 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>>>>>
>>>>>> Hi Rafael,
>>>>>>
>>>>>> Sorry, I'm still confused (my perpetual state :)).
>>>>>
>>>>> No worries, doing my best to address that.
>>>>>
>>>>>> On Fri, Nov 18, 2022 at 02:16:17PM +0100, Rafael J. Wysocki wrote:
>>>>>>> On Thu, Nov 17, 2022 at 11:16 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>>>>>>> On Thu, Nov 17, 2022 at 06:01:26PM +0100, Rafael J. Wysocki wrote:
>>>>>>>>> On Thu, Nov 17, 2022 at 12:28 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>>>>>>>>> On Wed, Nov 16, 2022 at 01:00:36PM +0100, Rafael J. Wysocki wrote:
>>>>>>>>>>> On Wed, Nov 16, 2022 at 1:37 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>>>>>>>>>>> On Mon, Nov 14, 2022 at 04:33:52PM +0100, Rafael J. Wysocki wrote:
>>>>>>>>>>>>> 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.
>>>>>>>>>>>>
>>>>>>>>>>>> Now I'm confused again about what "HotPlugSupportInD3" means.  The MS
>>>>>>>>>>>> web page [1] says it identifies Root Ports capable of handling hot
>>>>>>>>>>>> plug events while in D3.  That sounds kind of related to _S0W: If _S0W
>>>>>>>>>>>> says "I can wake myself from D3hot and D3cold", how is that different
>>>>>>>>>>>> from "I can handle hotplug events in D3"?
>>>>>>>>>>>
>>>>>>>>>>> For native PME/hot-plug signaling there is no difference.  This is the
>>>>>>>>>>> same interrupt by the spec after all IIRC.
>>>>>>>>>>>
>>>>>>>>>>> For GPE-based signaling, though, there is a difference, because GPEs
>>>>>>>>>>> can only be used directly for wake signaling (this is related to
>>>>>>>>>>> _PRW).  In particular, the only provision in the ACPI spec for device
>>>>>>>>>>> hot-add are the Bus Check and Device Check notification values (0 and
>>>>>>>>>>> 1) which require AML to run and evaluate Notify() on specific AML
>>>>>>>>>>> objects.
>>>>>>>>>>>
>>>>>>>>>>> Hence, there is no spec-defined way to tell the OS that "something can
>>>>>>>>>>> be hot-added under this device while in D3 and you will get notified
>>>>>>>>>>> about that".
>>>>>>>>>>
>>>>>>>>>> So I guess acpi_pci_bridge_d3() looks for:
>>>>>>>>>>
>>>>>>>>>>    - "wake signaling while in D3" (_S0W) and
>>>>>>>>>>    - "notification of hotplug while in D3" ("HotPlugSupportInD3")
>>>>>>>>>>
>>>>>>>>>> For Root Ports with both those abilities (or bridges below such Root
>>>>>>>>>> Ports), we allow D3, and this patch doesn't change that.
>>>>>>>>>>
>>>>>>>>>> What this patch *does* change is that all bridges with _PS0 or _PR0
>>>>>>>>>> previously could use D3, but now will only be able to use D3 if they
>>>>>>>>>> are also (or are below) a Root Port that can signal wakeup
>>>>>>>>>> (wakeup.flags.valid) and can wakeup from D3hot or D3cold (_S0W).
>>>>>>>>>>
>>>>>>>>>> And this fixes the Pink Sardine because it has Root Ports that do
>>>>>>>>>> Thunderbolt tunneling, and they have _PS0 or _PR0 but their _S0W says
>>>>>>>>>> they cannot wake from D3.  Previously we put those in D3, but they
>>>>>>>>>> couldn't wake up.  Now we won't put them in D3.
>>>>>>>>>>
>>>>>>>>>> I guess there's a possibility that this could break or cause higher
>>>>>>>>>> power consumption on systems that were fixed by c6e331312ebf
>>>>>>>>>> ("PCI/ACPI: Whitelist hotplug ports for D3 if power managed by ACPI").
>>>>>>>>>> I don't know enough about that scenario.  Maybe Lukas will chime in.
>>>>>>>>>
>>>>>>>>> Well, it is possible that some of these systems will be affected.
>>>>>>>>>
>>>>>>>>> One of such cases is when the port in question has _S0W which says
>>>>>>>>> that wakeup from D3 is not supported.  In that case I think the kernel
>>>>>>>>> should honor the _S0W input, because there may be a good reason known
>>>>>>>>> to the platform integrator for it.
>>>>>>>>>
>>>>>>>>> The other case is when wakeup.flags.valid is unset for the port's ACPI
>>>>>>>>> companion which means that the port cannot signal wakeup through
>>>>>>>>> ACPI-related means at all and this may be problematic, especially in
>>>>>>>>> the system-wide suspend case in which the wakeup capability is not too
>>>>>>>>> relevant unless there is a system wakeup device under the port.
>>>>>>>>>
>>>>>>>>> I don't think that the adev->wakeup.flags.valid check has any bearing
>>>>>>>>> on the _S0W check - if there is _S0W and it says "no wakeup from D3",
>>>>>>>>> it should still be taken into account - so that check can be moved
>>>>>>>>> past the _S0W check.
>>>>>>>>
>>>>>>>> So if _S0W says it can wake from D3, but wakeup.flags is not valid,
>>>>>>>> it's still OK to use D3?
>>>>>>>
>>>>>>> No, it isn't, as per the code today and I don't think that this
>>>>>>> particular part should be changed now.
>>>>>>
>>>>>> But the current upstream code checks acpi_pci_power_manageable(dev)
>>>>>> first, so if "dev" has _PR0 or _PS0, we'll use D3 even if _S0W says it
>>>>>> can wake from D3 and wakeup.flags is not valid.
>>>>>
>>>>> Yes, the current code will return 'true' if _PR0 or _PS0 is present
>>>>> for dev regardless of anything else.
>>>>>
>>>>> The proposed change is to make that conditional on whether or not _S0W
>>>>> for the root port says that wakeup from D3 is supported (or it is not
>>>>> present or unusable).
>>>>>
>>>>> I see that I've missed one point now which is when the root port
>>>>> doesn't have an ACPI companion, in which case we should go straight
>>>>> for the "dev is power manageable" check.
>>>>
>>>> Moreover, it is possible that the bridge passed to acpi_pci_bridge_d3() has its
>>>> own _S0W or a wakeup GPE if it is power-manageable via ACPI.  In those cases
>>>> it is not necessary to ask the Root Port's _S0W about wakeup from D3, so overall
>>>> I would go for the patch like the below (not really tested).
>>>>
>>>> This works in the same way as the current code (unless I have missed anything)
>>>> except for the case when the "target" bridge is power-manageable via ACPI, but
>>>> it cannot signal wakeup via ACPI and has no _S0W.  In that case it will consult
>>>> the upstream Root Port's _S0W to check whether or not wakeup from D3 is
>>>> supported.
>>>>
>>>> [Note that if dev_has_acpi_pm is 'true', it is kind of pointless to look for the
>>>> "HotPlugSupportInD3" property of the Root Port, because the function is going to
>>>> return 'true' regardless, but I'm not sure if adding an extra if () for handling
>>>> this particular case is worth the hassle.]
>>>
>>> I think this has a lot of potential.  I haven't tried it, but I wonder
>>> if splitting out the Root Port-specific parts to a separate function
>>> would be helpful, if only to make it more obvious that there may be
>>> two different devices involved.
>>>
>>> If there are two devices ("dev" is a bridge below a Root Port), I
>>> guess support in the Root Port is not necessarily required?  E.g.,
>>> could "dev" assert a wakeup GPE that's not routed through the Root
>>> Port?  If Root Port support *is* required, maybe it would read more
>>> clearly to test that first, before looking at the downstream device.
>>
>> Sorry for the delay.
>>
>> I don't really think that Root Port support is required for a bridge below
>> a Root Port if that bridge itself is power-manageable via ACPI.  Moreover,
>> I don't think that the _S0W of a Root Port has any bearing on devices below
>> it that have their own _S0W.
>>
>> So what we really want appears to be to evaluate _S0W for the target bridge,
>> regardless of whether or not it is a Root Port, and return 'false' if that
>> produces D2 or a shallower power state.  Otherwise, we can do what we've
>> done so far.
>>
>> The patch below implements, this - please let me know what you think.

This looks good to me, thanks.

>>
> 
> And here's a v2 with somewhat less code duplication.
> 
> ---
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Subject: [PATCH] PCI / ACPI: PM: Take _S0W of the target bridge into account in acpi_pci_bridge_d3(()
> 
> 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.
> 
> Reported-by: Mario Limonciello <mario.limonciello@....com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Reviewed-by: Mario Limonciello <mario.limonciello@....com>

> ---
>   drivers/acpi/device_pm.c |   16 ++++++++++++++++
>   drivers/pci/pci-acpi.c   |   34 ++++++++++++++++++++++++----------
>   include/acpi/acpi_bus.h  |    1 +
>   3 files changed, 41 insertions(+), 10 deletions(-)
> 
> Index: linux-pm/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-acpi.c
> +++ linux-pm/drivers/pci/pci-acpi.c
> @@ -977,22 +977,37 @@ bool acpi_pci_bridge_d3(struct pci_dev *
>   {
>   	struct pci_dev *rpdev;
>   	struct acpi_device *adev;
> -	acpi_status status;
> -	unsigned long long state;
>   	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_no_wakeup_from_d3(adev))
> +			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 (rpdev != dev)
> +		adev = ACPI_COMPANION(&rpdev->dev);
> +
>   	if (!adev)
>   		return false;
>   
> @@ -1005,11 +1020,10 @@ bool acpi_pci_bridge_d3(struct pci_dev *
>   		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 (rpdev != dev && acpi_dev_no_wakeup_from_d3(adev))
>   		return false;
>   
>   	/*
> 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 +484,22 @@ void acpi_dev_power_up_children_with_adr
>   	acpi_dev_for_each_child(adev, acpi_power_up_if_adr_present, NULL);
>   }
>   
> +/**
> + * acpi_dev_no_wakeup_from_d3 - Check if wakeup signaling from D3 is supported
> + * @adev: ACPI companion of the target device.
> + *
> + * Evaluate _S0W for @adev and return 'true' if it is successful and the power
> + * state returned by it is D2 or shallower.
> + */
> +bool acpi_dev_no_wakeup_from_d3(struct acpi_device *adev)
> +{
> +	unsigned long long state;
> +	acpi_status status;
> +
> +	status = acpi_evaluate_integer(adev->handle, "_S0W", NULL, &state);
> +	return ACPI_SUCCESS(status) && state < ACPI_STATE_D3_HOT;
> +}
> +
>   #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);
> +bool acpi_dev_no_wakeup_from_d3(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,
> 
> 
> 

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