kexec and frame buffer

[Luca Falavigna <dktrkranz@gmail.com>]

I made three experiments regarding kexec with frame buffer support (vesafb). For
each of them I gathered dmesg messages from original and relocated kernel, in
order to easily compare them later on. These tests were run on a virtual machine
in order to provide the same environment for each experiment.

Here are my tests and related results:



	1) Frame buffer not enabled

Original kernel command line: root=/dev/hda1 ro
Relocated kernel command line: root=/dev/hda1 ro

Everything went well, as supposed to be. I was able to read boot messages and to
see login prompts.


	2) Frame buffer enabled in the relocated kernel

Original kernel command line: root=/dev/hda1 ro
Relocated kernel command line: root=/dev/hda1 ro vga=791

This time I was able to read boot messages and so on, but I couldn't be able to
load vesafb in the relocated kernel. dmesg showed nothing about vesafb.


	3) Frame buffer enabled in the original kernel

Original kernel command line: root=/dev/hda1 ro vga=791
Relocated kernel command line: root=/dev/hda1 ro {vga=791,}

This time I wasn't able to read boot messages in the relocated kernel, whether
vga parameter was set or not. I looked at dmesg in order to get some useful
informations:

Linux version 2.6.13-rc5 (dktrkranz@gandalf) (gcc version 3.3.4 (Debian
1:3.3.4-13)) #3 Wed Aug 3 13:39:11 UTC 2005
[...]
-Console: colour dummy device 80x25
+Console: colour VGA+ 80x25
[...]
-vesafb: framebuffer at 0xf0000000, mapped to 0xc2880000, using 3072k, total
16384k
-vesafb: mode is 1024x768x16, linelength=2048, pages=0
-vesafb: protected mode interface info at 00ff:44f0
-vesafb: scrolling: redraw
-vesafb: Truecolor: size=0:5:6:5, shift=0:11:5:0
-mtrr: your processor doesn't support write-combining
-Console: switching to colour frame buffer device 128x48
-fb0: VESA VGA frame buffer device
[...]

It seems relocated kernel doesn't (or can't) load vesafb. Is frame buffer
supported in kexec or there is some work-in-progress?



Regards,
--
					Luca