[bug #40836] Document GRUB's preference for the EFI framebuffer on BIOS systems

[Eli]

URL:
  <http://savannah.gnu.org/bugs/?40836>

                 Summary: Document GRUB's preference for the EFI framebuffer
on BIOS systems
                 Project: GNU GRUB
            Submitted by: eliptus
            Submitted on: Sat 07 Dec 2013 07:08:53 PM GMT
                Category: Documentation
                Severity: Major
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 
                 Release: other
         Reproducibility: None
         Planned Release: None

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Details:

For background, please refer to https://savannah.gnu.org/bugs/?40552.

I'm currently using grub-2.00_p5107-r2 on Gentoo.  GRUB seems to have a
preference to use the EFI framebuffer when GRUB_VIDEO_BACKEND is unset, even
on BIOS systems, as confirmed by Vladimir on the aforementioned bug.  This is
nonintuitive, and users are unlikely to consider that they need to add EFI
support to their kernel for their BIOS system.  There are many forums on this
topic that have concluded with disabling graphics support in GRUB, to allow
the kernel to successfully use the appropriate framebuffer driver, such as
vesafb.

This warrants proper documentation in the GRUB manual.


Summary from Bug 40552:

I'm currently using grub-2.00_p5107-r2 on Gentoo. Using GRUB's default
configuration, but setting "GRUB_GFXPAYLOAD_LINUX=1024x768" in
/etc/default/grub would result in a blank screen unless I enabled "efifb" in
the kernel. This is unexpected since I'm running a BIOS system and the
framebuffer is expected to use "vesafb". 

As a test, I set "GRUB_VIDEO_BACKEND=true" in /etc/default/grub, disabling
GRUB's loading of it's video modules. Doing so resulted in the kernel
correctly matching the framebuffer to the "vesafb" driver. Further
experimentation showed that setting "GRUB_VIDEO_BACKEND=vbe" also resulted in
the correct behavior. 

Using "all_video" or any other video module incorrectly resulted in matching
of "efifb".




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