vesafb and too much RAM?

I was running debian with a 2.4.20(-3 I believe) with vesafb with no
problems with 512MB ram. I upgraded to 1GB and immediately I could not
boot. I get as far as the LILO prompt, but as soon as I hit enter the
screen goes black, the caps lock and scroll lock keyboard LEDs flash, and
nothing save hitting the reset switch has any affect.

I can append 'mem=768M' to the kernel command line and everything boots
like normal except of course that then it think I have only 768MB RAM. If
I tell the kernel not to use vesafb by removing the 'vga=' line in my
lilo.conf then everything boot fine and my RAM is recognized.

I also have a second install of debian with kernel 2.4.19 on the same
machine. With this kernel it actually boots, however the screen stays
black. I can log in blindly and issue commands and dmesg reported the
following:

"vesafb: abort, cannot ioremap video memory 0x8000000 @ 0xd8000000"

This kernel also behaves normally if I specify 'mem=768M' on the kernel
command line or if I specify vga=normal (overriding my normal vga=792 from
lilo.conf). With 'mem=768M' set dmesg shows:

 vesafb: framebuffer at 0xd8000000, mapped to 0xf080e000, size 131072k
 vesafb: mode is 1024x768x32, linelength=4096, pages=1
 vesafb: protected mode interface info at c000:e350
 vesafb: scrolling: redraw
 vesafb: directcolor: size=8:8:8:8, shift=24:16:8:0
 Console: switching to colour frame buffer device 128x48
 fb0: VESA VGA frame buffer device

with 2.4.20 and 'mem=768M'

 vesafb: framebuffer at 0xd8000000, mapped to 0xf0800000, size 131072k
 vesafb: mode is 1024x768x32, linelength=4096, pages=1
 vesafb: protected mode interface info at c000:e350
 vesafb: scrolling: redraw
 vesafb: directcolor: size=8:8:8:8, shift=24:16:8:0
 Console: switching to colour frame buffer device 128x48
 fb0: VESA VGA frame buffer device

In testing I have found that I can go as high as 'mem=880M' with no
problem but 'mem=881M' ends in the same results as described above.

I don't know if this is a bug or something I may have overlooked or failed
to do. Hope someone can understand whats happening.

Thanks and regards,
Matt N.



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