Bjorn, Krzysztof: could you please look at this patch series and say what do you think about it? It is quite strange issue for which is defined PCI_ANY_ID quirk... And is needs to be somehow workarounded. On Saturday 17 September 2022 13:03:05 Maciej W. Rozycki wrote: > Hi, > > This is v5 of the change to work around a PCIe link training phenomenon > where a pair of devices both capable of operating at a link speed above > 2.5GT/s seems unable to negotiate the link speed and continues training > indefinitely with the Link Training bit switching on and off repeatedly > and the data link layer never reaching the active state. > > This was originally observed in a configuration featuring a downstream > port of the ASMedia ASM2824 Gen 3 switch wired to the upstream port of the > Pericom PI7C9X2G304 Gen 2 switch. However in the course of review I have > come to the conclusion that similarly to the earlier similar change to > U-Boot it is indeed expected to be safe to apply this workaround to any > downstream port that has failed link negotiation provided that: > > 1. the port is capable of reporting the data link layer link active > status (because unlike U-Boot we cannot busy-loop continuously polling > the link training bit), > > and: > > 2. we don't attempt to lift the 2.5GT/s speed restriction, imposed as the > basis of the workaround, for devices not explicitly known to continue > working in that case. > > It is expected to be safe because the workaround is applied to a failed > link, that is one that does not (at the time this code is executed) work > anyway, so trying to bring it up cannot make the situation worse. So this > version of the workaround is attempted for all PCIe devices discovered, > and only the lifting of the 2.5GT/s speed restriction is qualified by the > vendor:device ID, currently one of the ASMedia ASM2824 device only. > > Broadening the scope of the quirk has in turn made it necessary to make > some adjustments to code elsewhere and consequently what was originally a > single patch has now become a small series instead. > > This has been verified with a SiFive HiFive unmatched board, booting with > or without the workaround activated in U-Boot, which covered both the link > retraining part of the quirk and the lifting of speed restriction already > imposed by U-Boot. > > Please see individual change descriptions for further details. > > Questions or comments? Otherwise please apply. > > Maciej
