Re: [PATCH v2] PCI/PM: Put devices to low power state on shutdown

["Mark Pearson" <mpearson-lenovo@squebb.ca>]

Hi,

On Sun, Dec 8, 2024, at 2:41 AM, Kai-Heng Feng wrote:
> Some laptops wake up after poweroff when HP Thunderbolt Dock G4 is
> connected.
>
> The following error message can be found during shutdown:
> pcieport 0000:00:1d.0: AER: Correctable error message received from 
> 0000:09:04.0
> pcieport 0000:09:04.0: PCIe Bus Error: severity=Correctable, type=Data 
> Link Layer, (Receiver ID)
> pcieport 0000:09:04.0:   device [8086:0b26] error 
> status/mask=00000080/00002000
> pcieport 0000:09:04.0:    [ 7] BadDLLP
>
> Calling aer_remove() during shutdown can quiesce the error message,
> however the spurious wakeup still happens.
>
> The issue won't happen if the device is in D3 before system shutdown, so
> putting device to low power state before shutdown to solve the issue.
>
> ACPI Spec 6.5, "7.4.2.5 System \_S4 State" says "Devices states are
> compatible with the current Power Resource states. In other words, all
> devices are in the D3 state when the system state is S4."
>
> The following "7.4.2.6 System \_S5 State (Soft Off)" states "The S5
> state is similar to the S4 state except that OSPM does not save any
> context." so it's safe to assume devices should be at D3 for S5.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=219036
> Cc: AceLan Kao <acelan.kao@canonical.com>
> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> Signed-off-by: Kai-Heng Feng <kaihengf@nvidia.com>
> ---
>  drivers/pci/pci-driver.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 35270172c833..248e0c9fd161 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -510,6 +510,14 @@ static void pci_device_shutdown(struct device *dev)
>  	if (drv && drv->shutdown)
>  		drv->shutdown(pci_dev);
> 
> +	/*
> +	 * If driver already changed device's power state, it can mean the
> +	 * wakeup setting is in place, or a workaround is used. Hence keep it
> +	 * as is.
> +	 */
> +	if (!kexec_in_progress && pci_dev->current_state == PCI_D0)
> +		pci_prepare_to_sleep(pci_dev);
> +
>  	/*
>  	 * If this is a kexec reboot, turn off Bus Master bit on the
>  	 * device to tell it to not continue to do DMA. Don't touch
> -- 
> 2.47.0

Just a note that we've tested this in the Lenovo Linux team and confirmed that it reduces the power draw on a powered off Z16 G2 by 0.6W.
This is enough to bring Linux inline with Windows, and more importantly allow the platform to pass e-star energy certification (which it otherwise fails). We suspect other platforms will show similar benefits.

Let me know if there's anything we can do to help get this patch moving along - I think it's important.

Tested-by: Mark Pearson <mpearson-lenovo@squebb.ca>

Mark