[Bug 91871] link retraining for DP not possible with current design of Atomic modeset framework

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91871

--- Comment #2 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
One potential idea came to mind recently; We could try to train the link to the
max immediately upon long hpd, and based on the maximum rate that was achieved
we could filter out modes that exceed it. That way userspace shouldn't be able
to request anything we can't deliver.

Unfortunately there are at least two problems with that apporach. First one
being fastboot. We can't try to train the link when taking over from the BIOS
without blinking the display, so we would either have to do that or limit the
modes to whatever bitrate the BIOS chose to use. The other problem being that
even if we initially succeed in training the link at a certain bitrate, there's
no guarantee we can repeat the same feat later eg. due to changing
environmental conditions. Though maybe this latter worry is a bit more
theoretical, not sure.

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