mm

讲述linux的初始化过程

The current state of Linux/PA-RISC mm is BROKEN.

Someone needs to sit down and thoroughly rewrite all the cache flushing
macro definitions.  Here are some of the problems, followed by what I
think needs to be done about them.

(1) We're using fdce / fice everywhere.  This has to stop (except in
the routines which flush the entire cache).  The right instructions to
be using are fdc/fic.

(2) fdc/fic will throw exceptions if the address they reference isn't
mapped.  Therefore we need to check the page is mapped before flushing
(we're guaranteed not to have the page dirty if we don't have a software
mapping for it any longer, right?)

(3) the flush macros are right now tunnelled down to one routine to flush
the data cache and one routine to flush the insn cache.  this is wrong.
we should take hints from how we're called and optimise our routines
accordingly.

(4) fdc/fic actually take space register arguments.  fic takes an 3-bit sr
argument and fdc takes a 2-bit sr argument.  right now, there's a lot of
pissing about with %sr1 and all the macros use %sr1.  This is crazy.  We
normally _know_ what's being referred to, and it's the current task.  So
if we want to flush that, just use %sr3.  If it happens to be kernel,
use %sr0 for fdc and %sr4 for fic.

(5) we need to write flush_kernel_dcache_range and use it on kernel
addresses.  all the macros are defined to work on the _current task's_
virtual address space.