Framebuffer can not be disabled in GRUB/UEFI mode

[jkirk]

In our GRUB configuration we have set gfxmode=auto, see:

grml-live/templates/boot/grub/header.cfg

Line 6 in 1df1f3d

set gfxmode=auto

The gfxmode documentation states that a platform-specific default "that should look reasonable" is selected as resolution (via VESA BIOS Extensions (VBE)).
For instance, in my QEMU instance a resolution of 1280x800 is selected by the GRUB boot menu.

It seems that once the resolutions has changed the framebuffer can not be disabled with the boot options.
Here the following boot options do not seem to work:

• "Disable Framebuffer"
• "Disable Video Kernel Mode Setting"

We should consider dropping them in the GRUB/UEFI boot menu (see below).

Note, that "Disable Framebuffer" (and "Serial Console") in Grub sets set gfxpayload=text. All other options have set gfxpayload=keep, see: %SHORT_NAME%_options.cfg

Quoting the gfxpayload documentation:

If this variable is set, it controls the video mode in which the Linux kernel starts up, replacing the ‘vga=’ boot option (see linux). It may be set to ‘text’ to force the Linux kernel to boot in normal text mode, ‘keep’ to preserve the graphics mode set using ‘gfxmode’, or any of the permitted values for ‘gfxmode’ to set a particular graphics mode (see gfxmode).

This means that set gfxpayload=text should actually work (with "Disable Framebuffer" ), but it does not...

Further:

Depending on your kernel, your distribution, your graphics card, and the phase of the moon, note that using this option may cause GNU/Linux to suffer from various display problems, particularly during the early part of the boot sequence. If you have problems, set this variable to ‘text’ and GRUB will tell Linux to boot in normal text mode.

As far as I can tell, we have no display problems, but we can not change back to text mode.
But again, we have gfxmode set. Maybe we should test without it?

The default is platform-specific. On platforms with a native text mode (such as PC BIOS platforms), the default is ‘text’. Otherwise the default may be ‘auto’ or a specific video mode.

sigh This makes it hard to test. I guess we use GRUB primarily with UEFI platforms. For BIOS platforms we use isolinux/syslinux. This means we just need to answer the question if we want UEFI systems to be able to boot in text mode or alike or drop everything regarding framebuffer / resolution and only keep the auto detection process.

[jkirk]

I think I already mentioned it somewhere (in grml/grml#9 and elsewhere), but we should investigate some more kernel parameters:

• video=vesafb:off
• video=efifb:off

Some links on this:

• https://passthroughpo.st/explaining-csm-efifboff-setting-boot-gpu-manually/

[jkirk]

Via @zeha
https://source.mnt.re/reform/reform-rk3588-uboot/-/blob/main/mnt-pocket-reform-rk3588_defconfig?ref_type=heads#L70

CONFIG_BOOTARGS="clk_ignore_unused cma=256M swiotlb=65535 fbcon=rotate:3 fbcon=font:TER16x32"

[mika]

I can confirm that fbcon=font:TER16x32 works nicely for the kernel part, thanks @jkirk + @zeha. But then later on in our boot process we're switching to our default and hardcoded font settings that are configured via console-setup.

Now that the console-setup was moved from grml-autoconfig (see grml/grml-autoconfig@4be463b + grml/grml-autoconfig@4f89bd4) towards grml-live's config/scripts/GRMLBASE/26-console-setup, what could we do to properly control this (as in: if one boots with fbcon=font:TER16x32 we don't override/modify it during booting)? 🤔

[zeha]

what could we do to properly control this (as in: if one boots with fbcon=font:TER16x32 we don't override/modify it during booting)? 🤔

Maybe we want to disable console-setup completely and pick a font for the default boot menu entry.

[mika]

what could we do to properly control this (as in: if one boots with fbcon=font:TER16x32 we don't override/modify it during booting)? 🤔

Maybe we want to disable console-setup completely and pick a font for the default boot menu entry.

Oh, nice idea, I like it! 👍 🙇

[jkirk]

I have a HP Elite x2 1012 G2 with a quite unusual HiDPI display resolution of 2736x1824.
I booted grml-full-daily20250217build238unstable-amd64.iso via Ventoy and from an USB Stick made with grml2usb and played around with a few options.

After a few hours of research and digging in the rabbit role, there are quite a few things to untangle:

• The answer to most of the following questions depend on: are we booting in legacy BIOS or UEFI. This issue is about Grub+UEFI but I also added links to options which could be useful for Grub+BIOS too.

  • There is no VGA/text console in UEFI mode, only in BIOS or legacy boot (see: https://forums.gentoo.org/viewtopic-t-1066642-start-0.html)

• Grub Output + Resolution:

  • GRUB_TERMINAL_OUTPUT: VGA text output (vga_text), graphics-mode output (gfxmode) or serial terminal (serial). Default is "platform’s native terminal output". I don't think we have any option than to keep the default, although a "force to serial output' option sounds interesting to me.
  • Links to Grub Framebuffer Resolution (GFXMODE) + vga= is deprecated + Kernel Resolution (GFXPAYLOAD)
    • https://wiki.archlinux.org/title/GRUB/Tips_and_tricks#Visual_configuration
    • https://www.gnu.org/software/grub/manual/grub/html_node/gfxmode.html
    • https://www.gnu.org/software/grub/manual/grub/html_node/gfxpayload.html
  • With Grub+UEFI we can not go back to text mode, so gfxpayload=text can be removed.
    gfxmode=auto should be fine.
  • Do we still use vga= somewhere?
  • Tools to test: hwinfo --framebuffer + fbset + videoinfo (in Grub command line)

• There are multiple framebuffer drivers: https://www.kernel.org/doc/html/latest/fb/index.html. Most notably:

  • efifb (EFI platform driver)
  • vesafb (generic driver for a graphic framebuffer on intel boxes)
  • fbcon (text console running on top of the framebuffer device)

• Graphics Output Protocol (GOP) is only accessible in a pre-boot environment (Boot Level vs. Kernel Level resolution (see: https://unix.stackexchange.com/a/777820)

• EFI provides two distinct video interfaces: GOP and UGA. VirtualBox provides a configuration option to control the graphics resolution for both interfaces 🤯: https://www.virtualbox.org/manual/topics/BasicConcepts.html#efividmode

• Do we want to support GPU passthrough? (see: https://passthroughpo.st/explaining-csm-efifboff-setting-boot-gpu-manually/ + https://wiki.gentoo.org/wiki/GPU_passthrough_with_virt-manager,_QEMU,_and_KVM)

• Do we want to change framebuffer resolution after boot? (https://packages.debian.org/bookworm/fbset)

• Do we want to change fonts and font size after boot (https://packages.debian.org/bookworm/console-setup)

Because you (@mika) used fbcon successfully, I took a closer look into the fbcon documentation, quoting a few sections:

A common bug report is enabling the framebuffer without enabling the framebuffer console. Depending on the driver, you may get a blanked or garbled display, but the system still boots to completion. If you are fortunate to have a driver that does not alter the graphics chip, then you will still get a VGA console.

Boot options: The framebuffer console has several, largely unknown, boot options that can change its behavior.

The fbdev drivers cannot be unloaded if bound to fbcon, and fbcon cannot be unloaded if it’s bound to the console layer.

Anyway, that is a lot to digest. Maybe we can discuss, what we want / expect and what we do not want.

[jkirk]

Decision from our meeting with @zeha + @mika (not all of the following to be handled in this issue):

• Drop "disable framebuffer" boot options (i.e. "Disable Framebuffer" + "Disable Video Kernel Mode Setting") from GRUB/UEFI boot menu
• Implement kernel options to set font + resolution early in the boot process to be consistent with what we get with console-setup
• Add a boot option for "large fonts"
• We want to be able to change font and/or the resolution after boot (add fbset + keep console-setup)
• We currently have not plans on supporting GPU passthrough. Ignoring for now
• Make sure grml-x looks "good" on high resolution displays
• We talked about moving away from X to wayland and switch the kind of obsolete window manager fluxbox. Some things we talked about:
  • https://github.com/wizbright/waybox
  • https://xfce.org/
  • https://wayfire.org/
  • https://swaywm.org/

[jkirk]

Some more infos + things I need to investigate:

• Boot options "Disable Framebuffer" + "Disable Video Kernel Mode Setting" have both the same kernel options:
  radeon.modeset=0 i915.modeset=0 nouveau.modeset=0 cirrus.modeset=0 mgag200.modeset=0 nomodeset
  Are they still useful?
• Grub Boot Menu by default seems to set to the "highest possible" resolution (for me 2736x1824). Which makes the fonts very small. I don't think this is something we want. We should stick to a "reasonable" resolution (gfxmode=1024x768?) OR change the font (see: https://askubuntu.com/a/1096354).
• Is it possible to change the resolution of the Grub menu on runtime?
• Is it possible to change the font of the Grub menu on runtime?
• FTR, the Grub Startup Sequence: https://www.gnu.org/software/grub/manual/grub-dev/grub-dev.html#Startup-Sequence. (It seems that once gfxmenu.mod is loaded, we can not change the mode?)
• Or can we? There is a grub_video_restore in the Video API.
• FTR, there is a The Definitive Guide To Theming GRUB 2 v1.99
• hwinfo --framebuffer is empty on my system, why? (Also see: https://unix.stackexchange.com/questions/649889/hwinfo-framebuffer-shows-nothing-cant-change-grub-resolution)
• journalctl -k | grep framebuffer shows efifb. Any other way to detect the framebuffer driver?
• • Framebuffer resolution can be queried (in Grub) with videoinfo
• Framebuffer resolution can be queried (after boot) with cat /sys/class/graphics/fb0/virtual_size (from: https://techoverflow.net/2015/06/21/querying-framebuffer-resolution-in-linux/)
• Framebuffer resolution can be set (after boot) with fbset

[jkirk]

Addendum:

journalctl -k | grep efifb looks like this on my system after a normal boot:

Feb 24 14:47:45 grml kernel: efifb: probing for efifb
Feb 24 14:47:45 grml kernel: efifb: framebuffer at 0x1fc0000000, using 19496k, total 19494k
Feb 24 14:47:45 grml kernel: efifb: mode is 2736x1824x32, linelength=10944, pages=1
Feb 24 14:47:45 grml kernel: efifb: scrolling: redraw
Feb 24 14:47:45 grml kernel: efifb: Truecolor: size=8:8:8:8, shift=24:16:8:0

When booting with video=efifb:off neither efifb nor framebuffer is mentioned in the logs:

Feb 25 15:30:53 grml kernel: Command line: BOOT_IMAGE=/boot/grmlfullamd64/vmlinuz apm=power-off boot=live findiso= nomce net.ifnames=0 live-media-path=/live/grml-full-amd64/ bootid=5cfce929-828c-402d-b1f3-e802c421e3a0 video=efifb:off
Feb 25 15:30:53 grml kernel: Kernel command line: BOOT_IMAGE=/boot/grmlfullamd64/vmlinuz apm=power-off boot=live findiso= nomce net.ifnames=0 live-media-path=/live/grml-full-amd64/ bootid=5cfce929-828c-402d-b1f3-e802c421e3a0 video=efifb:off

But I still get a (the same looking) high resolution console.