bugGNU GRUB - Bugs: bug #40836, Document GRUB's preference for the...

 
 

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

Submitted by:  Eli <eliptus>
Submitted on:  Sat 07 Dec 2013 07:08:53 PM UTC  
 
Category: DocumentationSeverity: Major
Priority: 5 - NormalItem Group: None
Status: NonePrivacy: Public
Assigned to: NoneOriginator Name: 
Open/Closed: OpenRelease: 
Release: otherReproducibility: None
Planned Release: None

Sat 07 Dec 2013 07:08:53 PM UTC, original submission:

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".

Eli <eliptus>

 

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