On 09/12/2021 14:31, Alex Deucher wrote:

[...] 
Once the driver takes over, none of the pre-driver state is retained.
You'll need to load the driver in the new kernel to initialize the
displays.  Note the efifb doesn't actually have the ability to program
any hardware, it just takes over the memory region that was used for
the pre-OS framebuffer and whatever display timing was set up by the
GOP driver prior to the OS loading.  Once that OS driver has loaded
the area is gone and the display configuration may have changed.

Hi Christian and Alex, thanks for the clarifications!

Is there any way to save/retain this state before amdgpu takes over?
Would simpledrm be able to program the device again, to a working state?

Finally, do you have any example of such a GOP driver (open source) so I
can take a look? I tried to find something like that in Tianocore
project, but didn't find anything that seemed useful for my issue.

Thanks again!