linux-kernel - Re: Lost PCIe PME after a914ff2d78ce ("PCI/ASPM: Don't select CONFIG

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Date:   Fri, 29 May 2020 21:40:38 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org
Subject: Re: Lost PCIe PME after a914ff2d78ce ("PCI/ASPM: Don't select
 CONFIG_PCIEASPM by default")

On 29.05.2020 21:21, Bjorn Helgaas wrote:
> [+cc Rafael, linux-kernel]
> 
> On Fri, May 29, 2020 at 08:50:46PM +0200, Heiner Kallweit wrote:
>> On 28.05.2020 23:44, Heiner Kallweit wrote:
>>> For whatever reason with this change (and losing ASPM control) I also
>>> loose the PCIe PME interrupts. This prevents my network card from
>>> resuming from runtime-suspend.
>>> Reverting the change brings back ASPM control and the PCIe PME irq's.
>>>
>>> Affected system is a Zotac MiniPC with a N3450 CPU:
>>> PCI bridge: Intel Corporation Celeron N3350/Pentium N4200/Atom E3900 Series PCI Express Port A #1 (rev fb)
>>>
>> I checked a little bit further and w/o ASPM control the root ports
>> don't have the PME service bit set in their capabilities.
>> Not sure whether this is a chipset bug or whether there's a better
>> explanation. However more chipsets may have such a behavior.
> 
> Hmm.  Is the difference simply changing the PCIEASPM config symbol, or
> are you booting with command-line arguments like "pcie_aspm=off"?
> 
Only difference is the config symbol. My command line is plain and simple:

Command line: initrd=\intel-ucode.img initrd=\initramfs-linux.img root=/dev/sda2 rw

> What's the specific PME bit that changes in the root ports?  Can you
> collect the "sudo lspci -vvxxxx" output with and without ASPM?
> 
> The capability bits are generally read-only as far as the PCI spec is
> concerned, but devices have implementation-specific knobs that the
> BIOS may use to change things.  Without CONFIG_PCIEASPM, Linux will
> not request control of LTR, and that could cause the BIOS to change
> something.  You should be able to see the LTR control difference in
> the dmesg logging about _OSC.
> 
>> W/o the "default y" for ASPM control we also have the situation now
>> that the config option description says "When in doubt, say Y."
>> but it takes the EXPERT mode to enable it. This seems to be a little
>> bit inconsistent.
> 
> We should probably remove the "if EXPERT" from the PCIEASPM kconfig.
> But I would expect PME to work correctly regardless of PCIEASPM, so
> removing "if EXPERT" doesn't solve the underlying problem.
> 
> Rafael, does this ring any bells for you?  I don't remember a
> connection between PME and ASPM, but maybe there is one.
> 
>> To cut a long story short:
>> At least on some systems this change has unwanted side effects.

lspci output w/ and w/o ASPM is attached incl. a diff.
Here comes the _OSC difference.

w/o ASPM

[    0.386063] acpi PNP0A08:00: _OSC: OS supports [ExtendedConfig Segments MSI HPX-Type3]
[    0.386918] acpi PNP0A08:00: _OSC: not requesting OS control; OS requires [ExtendedConfig ASPM ClockPM MSI]

w/ ASPM
[    0.388141] acpi PNP0A08:00: _OSC: OS supports [ExtendedConfig ASPM ClockPM Segments MSI HPX-Type3]
[    0.393648] acpi PNP0A08:00: _OSC: OS now controls [PME AER PCIeCapability LTR]

It's at least interesting that w/o ASPM OS doesn't control PME and AER.

View attachment "lspci.diff" of type "text/plain" (4268 bytes)

View attachment "lspci_vvxxx_w_aspm" of type "text/plain" (46288 bytes)

View attachment "lspci_vvxxx_wo_aspm" of type "text/plain" (46288 bytes)