On Tue, 24 Oct 2023 16:03:27 +0300 Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > On Tue, Oct 24, 2023 at 09:03:22AM +0000, Simon Ser wrote: > > On Tuesday, October 24th, 2023 at 09:36, Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote: > > > > > Are DP MST port numbers guaranteed to be tied to the physical hardware > > > configuration (e.g. how cables are connected) and therefore stable > > > across reboots? What about stable across kernel upgrades? > > > > > > If I knew that, I could perhaps manufacture a stable identifier in > > > userspace by replacing the parent connector ID with a stable connector > > > designator. > > > > Hm, my assumption is that these are stable, but maybe that's also wrong? > > Ville, Dmitry, do you know whether the DP MST port numbers are > > guaranteed stable across reboots when retaining the exact same hardware > > configuration (not the software, maybe the user upgraded the kernel)? > > I suspect in practice those should remain the same as long as the > topology didn't change, but I don't think there's anything in the > DP spec that actually guarantees that (eg. some branch device > could in theory reshuffle its port numbers on a whim). > > But there is no stable identifier for the corresponding SST > connector anyway so I don't know what you would even do with > stable port numbers. You mean the index in the array of connectors exposed to userspace is not stable either for the root DP connector? KMS device bus path + connector array index for hardwired connectors is what I've been imagining as stable enough for all end users. Thanks, pq
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