RFC: DSI/DRM multiplexer bridge

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Hi,

my platform has a DIP switch controlled multiplexer for MIPI DSI output 
signals. One output has a TI SN65DSI84 (LVDS) and the other output has a TI 
SN65DSI86 (eDP) attached to it. The Multiplexer status can be read back from a 
GPIO. The GPIO is also IRQ capable, so it would be possible to support hotplug 
additionally later on.

My initial idea was to create a DRM multiplexer bridge driver which (depending 
on the input GPIO) allows only one output to be enabled. Unfortunately ti-
sn65dsi86.c driver expects a DSI host on remote node 0 (see ti_sn_attach_host 
and ti_sn_bridge_parse_dsi_host), so it does not work. ti-sn65dsi83.c just 
requires a drm_bridge.

What is the best approach for this? I currently see two approaches:
* Create an explicit DSI/DRM multiplexer bridge driver which registers itself 
as DSI host
* Create a DRM multiplexer bridge (only). But this needs to remove the DSI 
device registration from ti-sn65dsi86.c

I am aware that DSI support is suboptimal, so I'm not sure which approach on 
the TI bridge drivers is the correct one and needs to be considered as given.
Any ideas?

Best regards,
Alexander
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