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Revision as of 02:43, 17 June 2012 by Jasonwryan (Talk | contribs) (Define a Resolution)

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In contrast with other framebuffer drivers, uvesafb needs a userspace virtualizing daemon, called v86d. It may seem foolish to emulate x86 code on a x86, but this is important if one wants to use the framebuffer code on other architectures (notably non-x86 ones). A new framebuffer driver has been added to kernel 2.6.24. It has many more features than the standard vesafb, including:

  1. Proper blanking and hardware suspension after delay
  2. Support for custom resolutions as in the system BIOS.

It should support as much hardware as vesafb.


Install the uvesafb package:

# pacman -S v86d

Prepare the System

Bootloader Modifications

Remove any framebuffer-related kernel boot parameter from the bootloader configuration to disable the old vesafb framebuffter for loading.


Remove all references to vga=xxx from kernel lines in /boot/grub/menu.lst to allow correct operation of uvesafb.


First edit /etc/default/grub/ commenting the GRUB_GFXPAYLOAD_LINUX=keep line.

Then regenerate grub.cfg via the standard script:

# grub-mkconfig -o /boot/grub/grub.cfg

In some cases you will have to disable KMS before attempting to boot into framebuffer: failure to do so would result in a pitch-black screen, leaving no option but to restart the machine with Template:Keypress. For Intel cards, this is accomplished by appending i915.modeset=0 to GRUB's entry.

Add a v86d HOOK

Add the v86d hook to HOOKS in /etc/mkinitcpio.conf to allow uvesafb to take over at boot time.

HOOKS="base udev v86d ..."

Configure uvesafb

Define a Resolution

The options for uvesafb are defined in /usr/lib/modprobe.d/uvesafb.conf which is the default file installed by the v86d package.

# This file sets the parameters for uvesafb module.
# The following format should be used:
# options uvesafb mode_option=<xres>x<yres>[-<bpp>][@<refresh>] scroll=<ywrap|ypan|redraw> ...
# For more details see:
# http://www.kernel.org/doc/Documentation/fb/uvesafb.txt
options uvesafb mode_option=1280x800-32 scroll=ywrap

To prevent your customizations being overwritten when the package is updated, make any changes and copy this file to /etc/modprobe.d/uvesafb.conf and then add an entry in the FILES section of /etc/mkinitcpio.conf pointing to your configuration file, like so:


Regenerate initramfs Images

Changes are commited via booting into the initramfs images. Thus, users need to regenerate the initramfs images for the kernel(s). The following example assumes the default Arch Linux kernel:

# mkinitcpio -p linux


Reboot the system to see the changes.

Listing Resolutions

A list of possible resolutions can be generated via the following command:

$ cat /sys/bus/platform/drivers/uvesafb/uvesafb.0/vbe_modes

Users can modify /usr/lib/modprobe.d/uvesafb.conf with any entry returned.

Either of following commands can be used to show the current framebuffer resolution as a sanity check to see that settings are honored:

$ cat /sys/devices/virtual/graphics/fbcon/subsystem/fb0/virtual_size
$ cat /sys/class/graphics/fb0/virtual_size

Uvesafb compiled into the kernel

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: please use the first argument of the template to provide a brief explanation. (Discuss in Talk:Uvesafb#)

If you compile your own kernel, then you can also compile uvesafb into the kernel and run v86d later, e.g. from /etc/rc.local. In this case, the options can be passed as kernel boot parameters in the format video=uvesafb:<options>. Please note that this solution is not viable in the case you want to combine uvesafb with 915resolution as suggested below.

The homepage of uvesafb

The home page of uvesafb is http://dev.gentoo.org/~spock/projects/uvesafb where you can find some detailed information (you can ignore any information concerning patches for the kernel, because uvesafb is now in the vanilla kernel; moreover some information in the site assumes that uvesafb is compiled in the kernel, while it is a module in the Arch Linux stock binary kernel).

Uvesafb and 915resolution

In the following, we address a more complex scenario. Many intel video chipsets for widescreen laptops are known to have a buggy BIOS, which does not support the main, native resolution of the wide screen! For this reason, 915resolution was created to patch the BIOS at boot time and allow the X server to use the widescreen resolution. Nowadays, the X server is able to do this without the help of 915resolution. However, 915resolution can be combined with uvesafb in order to obtain a widescreen framebuffer, without any need to launch X at all. In this case, we need to load uvesafb after having run 915resolution, so that uvesafb can resort to the proper resolution.


In this scenario, 915resolution needs to be compiled statically (since it is going to be in an initramfs, it can not be linked to external libraries). Thus you CAN NOT use the 915resolution package in the [community] repo. Look instead for 915resolution-staticAUR in the AUR. It compiles 915 resolution statically and provides a 915 resolution hook, so you can run 915resolution before loading uvesafb and get the patched resolution. So install 915resolution-static via makepkg and pacman.

The resolution

You need to edit the 915resolution hook in order to define the BIOS mode you want to replace and and the resolution you want to get. You can get information about all the options for 915resolution with:

915resolution -h

So edit /lib/initcpio/hooks/915resolution and modify the options for 915resolution:

run_hook ()
   msg -n ":: Patching the VBIOS..."
   /usr/sbin/915resolution 5c 1280 800
   msg "done."

In the default, 5c is the code of the BIOS mode to replace. You can get a list of the available BIOS video modes with 915resolution -l.

Note: You want to choose the code of a mode that you DO NOT need (neither in the framebuffer nor in X), because 915resolution will replace it with a new user-defined mode. In the above example, 1280 800 is the new desired resolution.

The HOOKS array

Add the 915resolution hook and, after it, the v86d hook to HOOKS in /etc/mkinitcpio.conf. Put them before the hooks for the keymap, the resume from suspension and the filesystems.

HOOKS="base udev 915resolution v86d ..."

Then you need to regenerate your initramfs with mkinitcpio (adjust the following command to your setup):

mkinitcpio -p linux


Uvesafb cannot reserve memory

Check if you forgot to remove any vga=xxx kernel parameter -- this overrides the UVESA framebuffer with a standard VESA one.

pci_root PNP0A08:00 address space collision + Uvesafb cannot reserve memory

This occurs on the Acer Aspire One 751h with the 2.6.34-ARCH kernel; whether it also occurs on other systems is unknown. Even without another framebuffer interfering with the uvesafb setup, uvesafb cannot reserve the necessary memory region.

You can fix this issue by adding the following to the kernel parameters in your bootloader's configuration.