[coreboot] "WARNING: BIOS bug: CPU MTRRs don't cover all of memory" loosing 2048MB of ram
enok at lysator.liu.se
Tue Oct 4 15:14:18 CEST 2011
I incidently put 5GB RAM in my hp/dl145_g1 motherboard (2x1g+6x512m) and
got the following error from Linux when booting:
"WARNING: BIOS bug: CPU MTRRs don't cover all of memory" loosing 2048MB
(The dl145_g1 is a dual-socket amdk8 board with four DIMM's per CPU socket).
After digging around in the coreboot code I noticed that if I changed
the last line in src/amd/amd_mtrr.c the generated MTRR was correct and
the problem was solved:
/* Now that I have mapped what is memory and what is not
* Setup the mtrrs so we can cache the memory.
- x86_setup_var_mtrrs(address_bits, 0);
+ x86_setup_var_mtrrs(address_bits, 1);
In cpu/x86/mtrr/mtrr.c the comments explains the last parameter in great
void x86_setup_var_mtrrs(unsigned int address_bits, unsigned int above4gb)
/* this routine needs to know how many address bits a given processor
* supports. CPUs get grumpy when you set too many bits in
* their mtrr registers :( I would generically call cpuid here
* and find out how many physically supported but some cpus are
* buggy, and report more bits then they actually support.
* If above4gb flag is set, variable MTRR ranges must be used to
* set cacheability of DRAM above 4GB. If above4gb flag is clear,
* some other mechanism is controlling cacheability of DRAM above 4GB.
So - what "some other mechanism" is assumed to work on AMD cpu's and
what should I do to make it work?
The patch described in
by Scott Duplichan tries to explain something, but I'm still not sure
what to do.
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