Messages in this thread | | | Date | Wed, 2 Aug 2023 09:10:38 -0500 | Subject | Re: [PATCH v7 2/2] PCI: Don't put non-power manageable PCIe root ports into D3 | From | Mario Limonciello <> |
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On 8/2/23 00:26, Mika Westerberg wrote: > Hi Mario, > > On Tue, Aug 01, 2023 at 10:17:11PM -0500, Mario Limonciello wrote: >>> Consequently, platform_pci_bridge_d3() will return false and the only >>> thing that may allow the port to go into D0 is the dmi_get_bios_year() >>> check at the end of pci_bridge_d3_possible(). >>> >>> However, that was added, because there are Intel platforms on which >>> Root Ports need to be programmed into D3hot on suspend (which allows >>> the whole platform to reduce power significantly) and there are no >>> ACPI device power management objects associated with them (Mika should >>> know the gory details related to this). It looks like under Windows >>> the additional power reduction would not be possible on those systems, >>> but that would be a problem, wouldn't it? >>> >> >> I've been thinking on this today, and I at least have a hypothesis about >> this behavior. Perhaps Windows is actually utilizing enabled PEP >> constraints to enforce what state device should be put into over Modern >> Standby cycles in the absence of ACPI objects. >> >> In the case of one of my problematic system the PEP constraints for the root >> port are: >> >> Package (0x04) >> { >> 0x00, >> "\\_SB.PCI0.GP17", >> 0x00, >> 0x00 >> }, >> >> That first 0x00 means the constraint isn't actually enabled for the root >> port. >> >> Mika, >> >> Could you get an acpidump from one of these problematic Intel systems so we >> can check the PEP constraints to see if this theory works? Or maybe you have >> some other ideas why this is different? > > The patch adding this was merged in 2016 and unfortunately I don't have > any of the ACPI dumps from them available anymore (and do not recall the > details either). I think these were Apollo Lake-P based systems with the > initial runtime D3cold and S0ix support at the time.
I scoured the web looking for acpidumps a bit an Apollo Lake system and came across this random bug report:
https://bugzilla.redhat.com/show_bug.cgi?id=1591307
"Intel(R) Celeron(R) CPU N3450 @ 1.10GHz (family: 0x6, model: 0x5c, stepping: 0x9)"
I looked at the acpidump, and I notice:
Low Power S0 Idle (V5) : 0
That means that Windows wouldn't actually be putting it into Modern Standby at suspend but would rather use S3.
Considering that result, could we perhaps adjust the check to:
if ((c->x86_vendor == X86_VENDOR_INTEL) && !(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0))
Or could we quirk the PCI root ports from Apollo Lake to opt into D3?
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