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

[Mario Limonciello <mario.limonciello@amd.com>]

On 9/11/2024 14:16, Mario Limonciello wrote:
> On 9/11/2024 14:05, Bjorn Helgaas wrote:
>> On Fri, Jul 12, 2024 at 02:24:11PM +0800, 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.
>>>
>>> I don't have a sniffer so this is purely guesswork, however I believe
>>> putting device to low power state it's the right thing to do.
>>
>> My objection here is that we don't have an explanation of why this
>> should matter or a pointer to any spec language about this situation,
>> so it feels a little bit random.
>>
>> I suppose the problem wouldn't happen if AER interrupts were disabled?
>> We already do disable them in aer_suspend(), but maybe that's not used
>> in the shutdown path?
>>
>> My understanding is that .shutdown() should turn off device interrupts
>> and stop DMA.  So maybe we need an aer_shutdown() that disables
>> interrupts?
>>
> 
> IMO I see this commit as two problems with the same solution.
> 
> I don't doubt that cleaning up AER interrupts in the shutdown path would 
> help AER messages, but you really don't "want" devices to be in D0 when 
> the system is "off" because even if the system is off some rails are 
> still active and the device might still be powered.
> 
> A powered device could cause interrupts (IE a spurious wakeup).

It's a bit of a stretch, but ACPI 7.4.2.5 and 7.4.2.6 are the closest 
corollary to a spec I can find.

"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."

https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/07_Power_and_Performance_Mgmt/oem-supplied-system-level-control-methods.html

> 
>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=219036
>>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.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 af2996d0d17f..4c6f66f3eb54 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
>>> -- 
>>> 2.43.0
>>>
>