Re: [PATCH] drm/doc: describe PATH format for DP MST

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Oct 24, 2023 at 09:03:22AM +0000, Simon Ser wrote:
> On Tuesday, October 24th, 2023 at 09:36, Pekka Paalanen <ppaalanen@gmail.com> 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.

-- 
Ville Syrjälä
Intel