How do we want to deal with 4k tiled displays?

[Keith Packard]

Aaron Plattner <aplattner at nvidia.com> writes:

>  1. Hide the presence of the second tile in the X server.
>
>     Somehow combine the two tiles into a single logical output at the RandR
>     protocol level.  The X server would be responsible for setting up the right
>     configuration to drive the logical output using the correct physical
>     resources.

This is effectively what we do with the wacky ivybridge 3-output
setup. With that chipset, there are 4 DP lanes available and two
connectors. If you suck up all 4 lanes for the first connector, then you
have none left for the second one. If you've already configured the
second one, then you can't use the higher resolution modes on the first
one. The only way to tell is to try and see what RandR says.

RandR is always allowed to say 'no' to any particular configuration, and
in the tiled case, I'd suggest that the correct approach would be to
have the driver pretend that the monitor is connected to only one of the
outputs, and that configuring the 4k mode would require that sufficient
resources be available to drive both physical links.

-- 
keith.packard at intel.com
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