Re: [PATCH v7 05/12] PCI/PM: Disable device wakeups when halting or powering off system

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Sep 09, 2025 at 02:16:12PM -0500, Mario Limonciello (AMD) wrote:
> PCI devices can be configured as wakeup sources from low power states.
> However, when the system is halting or powering off such wakeups are
> not expected and may lead to spurious behavior.

I'm a little unclear on the nomenclature for these low power states,
so I think it would be helpful to connect to the user action, e.g.,
suspend/hibernate/etc, and the ACPI state, e.g.,

  ... when the system is hibernating (e.g., transitioning to ACPI S4
  and halting) or powering off (e.g., transitioning to ACPI S5 soft
  off), such wakeups are not expected ...

When I suspend or power off my laptop from the GUI user interface, I
want to know if keyboard or mouse activity will resume or if I need to
press the power button.

> ACPI r6.5, section 16.1.5 notes:
> 
>     "Hardware does allow a transition to S0 due to power button press
>      or a Remote Start."

Important to note here that sec 16.1.5 is specifically for "S5 Soft
Off State".

S4 is a sleeping state and presumably sec 16.1.6 ("Transitioning from
the Working to the Sleeping State") applies.  That section mentions
wakeup devices, so it's not obvious to me that PCI device wakeup
should be disabled for S4.

> This implies that wakeups from PCI devices should not be relied upon
> in these states. To align with this expectation and avoid unintended
> wakeups, disable device wakeup capability during these transitions.
> 
> Tested-by: Eric Naim <dnaim@cachyos.org>
> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
> ---
> v7:
>  * Reword title
>  * Reword commit
> v5:
>  * Re-order
>  * Add tags
> v4:
>  * https://lore.kernel.org/linux-pci/20250616175019.3471583-1-superm1@kernel.org/
> ---
>  drivers/pci/pci-driver.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 63665240ae87f..f201d298d7173 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -1139,6 +1139,10 @@ static int pci_pm_poweroff(struct device *dev)
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>  
> +	if (device_may_wakeup(dev) &&
> +	    (system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF))
> +		device_set_wakeup_enable(dev, false);
> +
>  	if (pci_has_legacy_pm_support(pci_dev))
>  		return pci_legacy_suspend(dev, PMSG_HIBERNATE);
>  
> -- 
> 2.43.0
>