dell 2850 memory mapping

michalwd1979 michalwd1979 at o2.pl
Fri Oct 19 05:22:03 CDT 2007


Hello,

I have found this old post on linux-pe list, originally written by Roger White. These are exactly the same problems that I have with my system now. I tried some tricks with /proc/mtrr, but I can not set any write-combining region. Does anyone know any fix to this? It seems that mtrrs are messed up but do You all have the same problems? Or is this only my problem with specific linux distro or something?
Please help, Michael.

2850, BIOS A02, 4GB memory.

There is something weird going on with the BIOS memory mapping.

Linux 64GB SMP kernel (Distro is irrelevant, 2.6 kernel) - From boot.msg :
<4> BIOS-e820: 0000000000000000 - 00000000000a0000 (usable)
<4> BIOS-e820: 0000000000100000 - 00000000cffc0000 (usable)
<4> BIOS-e820: 00000000cffc0000 - 00000000cffcfc00 (ACPI data)
<4> BIOS-e820: 00000000cffcfc00 - 00000000cffff000 (reserved)
<4> BIOS-e820: 00000000e0000000 - 00000000fec90000 (reserved)
<4> BIOS-e820: 00000000fed00000 - 00000000fed00400 (reserved)
<4> BIOS-e820: 00000000fee00000 - 00000000fee10000 (reserved)
<4> BIOS-e820: 00000000ffb00000 - 0000000100000000 (reserved)
<4> BIOS-e820: 0000000100000000 - 0000000130000000 (usable)

 From /proc/mtrr :
reg00: base=0x00000000 (   0MB), size=4096MB: write-back, count=1
reg01: base=0x100000000 (4096MB), size= 512MB: write-back, count=1
reg02: base=0x120000000 (4608MB), size= 256MB: write-back, count=1
reg03: base=0xd0000000 (3328MB), size= 256MB: uncachable, count=1
reg04: base=0xe0000000 (3584MB), size= 512MB: uncachable, count=1

Errr, three-quarter gig normal memory space as uncachable ?


The onboard VGA in the 2850 is a stripped ATI Radeon with 16MB VRAM.
However, lspci -v (snip) :
0000:09:0d.0 VGA compatible controller: ATI Technologies Inc Radeon RV100 
QY [Radeon 7000/VE] (prog-if 00 [VGA])
         Subsystem: Dell: Unknown device 016d
         Flags: bus master, VGA palette snoop, stepping, medium devsel, 
latency 32, IRQ 7
         Memory at d0000000 (32-bit, prefetchable) [size=128M]
         I/O ports at bc00 [size=256]
         Memory at df3f0000 (32-bit, non-prefetchable) [size=64K]
         Expansion ROM at df300000 [disabled] [size=128K]
         Capabilities: [50] Power Management version 2

Xorg correctly determines it has only 16MB but fails to get the 
write-combining area :
kernel: mtrr: type mismatch for d0000000,1000000 old: write-back new: 
write-combining


Any thoughts/comments ?

Roger While





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