Re: [PATCH] PCI/ASPM: Don't reconfigure ASPM entering low-power state

[Carlos Bilbao <carlos.bilbao.osdev@gmail.com>]

Hey Bjorn.

On 5/6/26 11:10, Bjorn Helgaas wrote:
> On Mon, Apr 27, 2026 at 09:01:04PM -0700, Carlos Bilbao (Lambda) wrote:
>> From: Carlos Bilbao <carlos.bilbao@kernel.org>
>>
>> Reconfiguring ASPM when a device transitions to low-power state can enable
>> L1.1/L1.2 substates on the PCIe link at a time when the device is sleeping
>> and may be unable to exit them. ASPM should be reconfigured on D0 entry
>> (resume), not on the way down.
>>
>> pci_set_low_power_state() calls pcie_aspm_pm_state_change() after writing
>> D3hot to PCI_PM_CTRL. pcie_aspm_pm_state_change() resets link->aspm_capable
>> to link->aspm_support and then calls pcie_config_aspm_path(), which can
>> enable ASPM L1.1/L1.2 substates on the PCIe link. If the device cannot
>> recover the link from L1.2 while in D3hot, subsequent config space reads
>> return 0xFFFF ("device inaccessible") and pci_power_up() fails with message
>> "Unable to change power state from D3hot to D0, device inaccessible".
> Carlos, do you have a few lines of dmesg showing this issue that we
> could quote to help people match the issue with this fix?


Thank you for reviewing this. Only the error message:

[160459.607156] vfio-pci 0000:5d:00.0: Unable to change power state from 
D3cold to D0, device inaccessible


Thanks,

Carlos