Random comments on LinuxBIOS

Steve Gehlbach steve at nexpath.com
Thu Apr 17 11:43:01 CEST 2003

Eric W. Biederman wrote:

>>I also think we should default to
>>wp cacheing for the flash region as well.
> WP caching??  We should cache it certainly but note
> that WP caching != Write Protect in the normal sense.
> Except for the location the 16->32bit transition this is pretty much
> what the code currently does.  And for our ``normal'' images when
> we have 2 copies of LinuxBIOS the start up is entirely 32bit.

I was referring to memory type=5, which Intel calls WP (vol 3, 10-23). 
It is not by default done for the upper 4G regions in linuxbios AFAIK 
(biosbase=0xffff0000).  One has to set XIP_ROM_BASE, XIP_ROM_SIZE, and 
then an mtrr is set of type 5 for this region, I am pretty sure.  It 
made a big difference in the pcchips787, as I could not use compression 
otherwise, took too long to decompress, and the watchdog reset kicked 
off.  I have not studied in detail what WP means precisely but I know 
that others use this type for flash regions.


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