[PATCH v4 04/11] drm/bridge: Make the bridge chain a double-linked list

[Sam Ravnborg]

Hi Boris.

> Just a reminder of my 2 proposals:
> 
> 1/ implement the bridge_ops->pre_enable/post_disable() hooks so you can
>    split your enable/disable logic in 2 parts and make sure things are
>    ready when the panel/next bridge tries to send DSI commands
> 2/ move everything that's needed to send DSI commands out of the
>    ->enable() path (maybe in runtime PM resume/suspend hooks) so you
>    can call that in the DSI transfer path too
> 
> As pointed out by Laurent, #1 doesn't work because some panel drivers
> send DSI commands in their ->prepare() hook, and ->pre_enable() methods
> are called in reverse order, meaning that the DRM panel bridge driver
> would try to issue DSI commands before the DSI host controllers is ready
> to send them. I still thing #2 is a good option.

Jitao Shi suggested to extend panels so we had a sequence of:

  prepare_power()  <= new callback,
                   here one should NOT be allowed to send
                   DSI commands
  prepare()
  enable()

   #
   # panel is now ready to show your favourite christmas movie
   #

  disable()
  unprepare()
  unprepare_power()  <= new callback


Would this help implement what you suggest above?
Relevant panels would then have to be updated - but this
is doable.

	Sam