[v3] atomics

[David Miller]

From: David Daney <ddaney@avtrex.com>
Date: Fri, 18 Apr 2008 10:51:33 -0700

> At this point I don't really have an opinion as to how to fix the 
> problem.  One thought that comes to mind is to change the definition of 
> atomic_flag so that the size of the atomic variable is appropriate for 
> the target architecture (32 bits in the case of MIPS)

It's trivial to synthesize 1-byte and 2-byte atomics if you only have
word sized ones.

You compute a shift and a mask based upon the offset of the byte
within the word, and then do your LL/SC sequence, shifting and masking
the byte you want to change in and out of the word.