[PATCH 0/1] console/fbcon: Add support for deferred console takeover

[Hans de Goede]

Hi All,

Allthough this patch has turned out pleasantly small / simpel, I guess
it still might be somewhat controversial. So let me explain why this
patch is necessary.

Various (desktop oriented) Linux distributions have spend a lot of time
to not show way too technial boot messages to end users during bootup.
What we would really like for the boot experience is something like
MacOS X / Windows 10 do. The (EFI) firmware boots up a logo and we
leave that in place until the login-manager (e.g. gdm) starts and then
the login-manager takes over the framebuffer including the current logo
contents and fades that into the login screen.

I've already written and upstreamed a patch for shim to not switch the
EFI framebuffer to text-mode, unless it has some error message to display
this is upstream now:
https://github.com/rhboot/shim/commit/1ff4a36a23ac5c17144275ccb3e1e1061750a137

I've written a similar patch for grub2 to not switch to text-mode when
using timeout_style=hidden for the menu and no key to show the menu is
pressed. This has been posted upstream and I need to do a v2 addressing
some small remarks.

This brings us to the next piece of software taking over control of
the framebuffer, the kernel.

I already have a patch in -next to fix the i915 driver not taking over
the BIOS used framebuffer (and thus loosing the vendor logo) on newer
hardware:
https://cgit.freedesktop.org/drm-intel/commit?id=011f22eb545a35f972036bb6a245c95c2e7e15a0

But this is only useful if we don't get fbcon binding to any fbdev
devices showing up and replacing there contents with a black screen
right away.

That is where this patch comes in it defers fbcon binding to any registered
fbdevs, until some output, any output at all, is send to the console (tty0),
this way error messages will still get shown, but a well behaved userspace
which does not spam the console with messages will retain the vendor logo
from the EFI firmware all the way to the login screen.

Regards,

Hans