Delay in copying Linuxbios to ram

Steve Gehlbach steve at nexpath.com
Mon Apr 28 15:11:01 CEST 2003


Eric W. Biederman wrote:

> ``Write Protect'' in the mtrrs does not mean write protected.  It is a strange
> messed up form of write-through.  In particular it dumps the cache on writes
> it does not forbid writes.
> 
> Unless you know of a situation where write protect is more appropriate please
> use write-through.  It is less confusing, and since no one is writing to that
> area anyway it gives the exact same result, reads are cached.
> 
> Eric

Good point, but do you think it would matter for reflashing?. I don't 
know if Linux resets the MTRRs when booting, or assumes the BIOS has 
already done that.  I got into the habit of using the WP setting because 
MS does it this way for the ROM areas for the Xbox (copying MS is 
probably not a good reason for doing anything!). For all to reference, 
Intel manual:

• Write protected (WP)—Reads come from cache lines when possible, and 
read misses cause cache fills. Writes are propagated to the system bus 
and cause corresponding cache lines on all processors on the bus to be 
invalidated. Speculative reads are allowed. This memory type is 
available in the Pentium 4, Intel Xeon, and P6 family processors by
programming the MTRRs (seeTable 10-6).
---------

-Steve





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