linux-kernel - Re: [PATCH v7 2/2] PCI: Don't put non-power manageable PCIe root ports into D3

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Date:   Mon, 31 Jul 2023 22:25:05 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
        linux-acpi@...r.kernel.org, Iain Lane <iain@...ngesquash.org.uk>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v7 2/2] PCI: Don't put non-power manageable PCIe root
 ports into D3

On 7/14/23 19:46, Limonciello, Mario wrote:
> 
> On 7/14/2023 2:17 PM, Rafael J. Wysocki wrote:
>>>> Generally speaking, pci_bridge_d3_possible() is there to prevent
>>>> bridges (and PCIe ports in particular) from being put into D3hot/cold
>>>> if there are reasons to believe that it may not work.
>>>> acpi_pci_bridge_d3() is part of that.
>>>>
>>>> Even if it returns 'true', the _SxD/_SxW check should still be applied
>>>> via pci_target_state() to determine whether or not the firmware allows
>>>> this particular bridge to go into D3hot/cold.  So arguably, the _SxW
>>>> check in acpi_pci_bridge_d3() should not be necessary and if it makes
>>>> any functional difference, there is a bug somewhere else.
>>> But only if it was power manageable would the _SxD/_SxW check be
>>> applied.  This issue is around the branch of pci_target_state() where
>>> it's not power manageable and so it uses PME or it falls back to D3hot.
>> Well, this looks like a spec interpretation difference.
>>
>> We thought that _SxD/_SxW would only be relevant for devices with ACPI
>> PM support, but the firmware people seem to think that those objects
>> are also relevant for PCI devices that don't have ACPI PM support
>> (because those devices are still power-manageable via PMCSR).  If
>> Windows agrees with that viewpoint, we'll need to adjust, but not
>> through adding _SxW checks in random places.
> I think that depends upon how you want to handle the lack of _S0W.
> 
> On these problematic devices there is no _S0W under the PCIe
> root port.  As I said; Windows puts them into D0 in this case though.
> 
> So acpi_dev_power_state_for_wake should return ACPI_STATE_UNKNOWN.
> 
> Can you suggest where you think adding a acpi_dev_power_state_for_wake() 
> does make sense?
> 
> Two areas that I think would work would be in: pci_pm_suspend_noirq() 
> (to avoid calling pci_prepare_to_sleep)
> 
> or
> 
> directly in pci_prepare_to_sleep() to check that value in lieu of 
> pci_target_state().
> 

Rafael,

Did you have any more thoughts on this?