HOWTO Framebuffer Support

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Framebuffer

[edit] Introduction

A framebuffer enables the kernel to display graphics on an otherwise text only console. These drivers can also be used for other things, such as running a non-accelerated X server or playing video in media players with framebuffer support. Framebuffer support is a requirement for gensplash and Qingy.

[edit] Kernel 2.6.x

Make your way to the kernel source directory, cd /usr/src/linux usually gets you there, and run make menuconfig. The relevant entries are located under Device Drivers -> Graphics support as seen here:

Device Drivers ->
 Graphics support ->
  [*]   Support for frame buffer devices
  [*]   Enable firmware EDID
  ---   Frame buffer hardware drivers
  ...
        Console display driver support ->
  [*]   Video mode selection support
  < >   Framebuffer Console support

You almost definitely want to tick Enable firmware EDID. If you notice that the kernel is taking a long time to load, disable it.

Listed below Frame buffer hardware drivers are the actual hardware drivers.

[edit] Commons

The kernel will only use the framebuffer if it is specifically told to do so. The required kernel command line option here is video= followed by the desired driver, a set of options, resolution, color depth and refresh rate. A uvesafb example is shown below, but keep in mind that how the kernel is told to use the framebuffer differs from driver to driver.

...
title=Gentoo Linux
root(hd0,0)
kernel /boot/bzImage root=/dev/hda3 video=uvesafb:ywrap,mtrr:3,1024x768-32@70
...

Here we told the kernel to use the uvesafb driver with the ywrap and mtrr:3 options, set the resolution to 1024x768 with a color depth of 32 bits and a refresh rate of 70Hz.

[edit] MTRR

The mtrr option defaults to mtrr:0, meaning that MTRR will be disabled — equivalent to the nomtrr option. The safest option is probably to use mtrr:1 and the most optimal option is most likely mtrr:3. The values represent:

0 - Disabled (equivalent to nomtrr) (default)

1 - Uncacheable

2 - Write-back

3 - Write-combining

4 - Write-through

Review the kernel documentation for more information.

[edit] ypan, ywrap and redraw

The ypan, ywrap and redraw are scrolling options. They set the way the kernel will handle the scrolling and panning of the framebuffer. If none of these are specified, the redraw option will be used, this is the safest but slowest option. Most modern hardware can handle ywrap, so this is most likely the option you want to use. If that fails you could try ypan, expect flickering using this though.

To clarify, a complete kernel command line in /boot/grub/grub.conf, using the uvesafb driver, with the mtrr:3 and ywrap options using a resolution of 1600x1200, a color depth of 32 bits and a refresh rate of 70 Hz would be:

...
kernel /boot/bzImage root=/dev/hda3 video=uvesafb:1600x1200-32@70,mtrr:3,ywrap
...

Review the Kernel Documentation for more information.

[edit] uvesafb

Some tinkering is involved to get the uvesafb driver working. You will need to enable Connector - unified userspace <-> kernelspace linker and Userspace VESA VGA graphics support.

Device Drivers ->
 <*>   Connector - unified userspace <-> kernelspace linker  --->
 ...
 Graphics support ->
  <*>   Userspace VESA VGA graphics support

Rebuild the kernel, but don't install it just yet. Emerge the klibc:

# emerge -av klibc

The reason we first needed to build the kernel is that we need klibc to compile against a kernel with Connector - unified userspace <-> kernelspace linker and Userspace VESA VGA graphics support enabled.

Next we need the v86d userspace helper:

# emerge -av v86d

Now, enable Initial RAM filesystem and RAM disk (initramfs/initrd) support in the kernel and set /usr/share/v86d/initramfs as the Initramfs source file(s)

General Setup ->
 [*] Initial RAM filesystem and RAM disk (initramfs/initrd) support
 (/usr/share/v86d/initramfs) Initramfs source file(s)

Rebuild the kernel yet again and finally install it.

Add to the kernel line of your /boot/grub/grub.conf, substituting the options to your liking:

...
kernel /boot/bzimage root=/dev/hda3 video=uvesafb:mtrr:3,ywrap,1024x768-24@60
...

Review the uvesafb Kernel Documentation or visit the official uvesafb website for more information.

[edit] vesafb

The vesafb driver is a generic VESA driver that works with most VESA compatible cards.

Device Drivers ->
 Graphics support ->
  [*]   VESA VGA graphics support

If you use the vesafb driver you will need to omit the resolution, color depth and refresh rate from the video= and follow with a vga= parameter. The vga= takes a hex value, omitting the 0x, or ask. Setting vga=ask is a good idea if you are unsure what to use, as the kernel will stop and ask you for the desired resolution and color depth.

Valid VGA modes are as follows:

For example, video=vesafb:mtrr:3,ywrap vga=0x792 would be equivalent to video=uvesafb:mtrr:3,ywrap,1024x768-24@60. Review the vesafb Kernel Documentation for more information.

[edit] sisfb

For users with a SiS card, you want the sisfb driver.

Device Drivers ->
 Graphics support ->
  <*>   SiS/XGI display support

This driver supports the following SiS cards:

• SiS 300 series: SiS 300/305, 540, 630(S), 730(S)
• SiS 315 series: SiS 315/H/PRO, 55x, (M)65x, 740, (M)661(F/M)X, (M)741(GX)
• SiS 330 series: SiS 330 ("Xabre"), (M)760

The video= parameter differs from other drivers. The uvesafb driver entry video=uvesafb:ypan,mtrr:3,1024x768-32@70 would be video=sisfb:mode:1024x768x32,rate:70,mem:4096 for sisfb.

[edit] Related Links

1. gensplash support
2. Bootsplash HOWTO
3. Qingy