Switching fb backend back to default

[Greg V]

On Sun, Mar 17, 2019 at 3:07 PM, Johannes Lundberg <johalun0 at gmail.com> 
wrote:
> Hi
> 
> I'm working on making i915kms unload properly. I've come to what I 
> think
> is the last issue. The drm driver unloads ok, the "efifb" backend is
> restored (according to logs) and vt_efifb_init() is being called but 
> the
> screen (laptop built in display) stays black. The system seems
> operational otherwise. If I load i915kms again in this state I get 
> back
> a visible (i915kms) framebuffer.
> 
> Did we ever have this working so it's known to work?

Recently on the linux kernel mailing list:

http://lkml.iu.edu/hypermail/linux/kernel/1903.1/01162.html

 > Of course, once native drivers like i915 or radeon take over, such a 
framebuffer is toast... [6]

 > [6] 
linux/drivers/gpu/drm/i915/i915_drv.c::i915_kick_out_firmware_fb()
 > linux/drivers/gpu/drm/radeon/radeon_drv.c::radeon_pci_probe()

So it seems like efifb is not supposed to work after a driver has been 
loaded at least once.