Re: [PATCH 0/1] PCI: Add CONFIG_PCI_NOSPEED_QUIRK to remove pcie_failed_link_retrain

[Matthew W Carlis <mattc@purestorage.com>]

On Fri, 18 Jul 2025, Maciej W. Rozycki wrote:
>  Bjorn, unfortunately sometimes you have to live with what you've got, in 
> particular there's (I believe still) no good choice available to replace 
> the HiFive Unmatched board and the PCIe splitter adapter chosen was the 
> only one I could chase that is fully mechanically compatible with *ATX 
> case slot space (i.e. you can actually properly mount it there next to the 
> mainboard and no connector will clash with another part of the system).
>
>  Matthew, please correct me if I'm wrong, but from discussion so far here 
> and previously I infer the problematic part is not the essential part of 
> the quirk, that is retraining at 2.5GT/s.  It is leaving the speed clamp 
> behind that is.

I'm just not sure what the benefit of the quirk is generally. It seems like
there are several problems with it in "well behaved" systems. I think for
people who build & sell servers they would go out and qualify a list of
devices which they will tell their customers "have been seen to work" &
therefore would be unlikely to see your specific issue. Another problem in my
mind with the quirk is that you're left trying to figure out if it should
have invoked the quirk before looking at the device interaction & so I think it
makes things a bit harder to debug.

In a way we're basically enabling future bad hardware by allowing the quirk to
run broadly on PCIe devices... Once its been around for a while will anyone ever
be able to confidently say its not necessary? In addition it sounds like both Ilpo
and I have observed LBMS to behave differently on different devices.