Re: [PATCH] PCI/ASPM: Enable L0s/L1 for removable devices when BIOS didn't configure ASPM

[Mario Limonciello]

On 5/5/26 11:05, Bjorn Helgaas wrote:
> On Mon, May 04, 2026 at 05:52:46PM -0500, Mario Limonciello wrote:
> > When comparing lspci output between Windows and Linux for hotplugged
> > Thunderbolt 5 eGPU devices, Windows enables ASPM L1 but Linux doesn't:
> >
> >    Windows: LnkCtl: ASPM L1 Enabled
> >    Linux:   LnkCtl: ASPM Disabled
> >
> > This difference in ASPM configuration can cause behavioral differences
> > between the two operating systems for the same hardware.
>
> A tangent, not a comment on the patch itself, but what sort of
> behavioral differences are these?  If ASPM is working correctly, the
> only differences *should* be in power consumption and performance.

This originally stemmed from a significant performance difference that 
was observed between Windows and Linux with eGPUs.  The link in the 
patch points at that bug if you want to look more closely at it.

I was hopeful that aligning ASPM would align the behavior, but alas this 
didn't.

It was still a difference that I figured we should discuss whether it 
should be changed to be consistent.