[ARM] Update ARM README

Provide more detailed information on machine types and machine
classes.

Documentation/arm/README

@@ -165,20 +165,34 @@ CONFIG_MACH_ and CONFIG_ARCH_
 
 Kernel entry (head-armv.S)
 --------------------------
-  The initial entry into the kernel made via head-armv.S uses architecture
+  The initial entry into the kernel is via head-armv.S, which uses machine
   independent code.  The machine is selected by the value of 'r1' on
-  entry, which must be kept unique.  You can register a new machine
-  by mailing the following details to rmk@arm.linux.org.uk  Please give
-  the mail a subject of 'Register new machine':
+  entry, which must be kept unique.
 
-    Name: <name of your machine>
-    ArchDir: <name of include/asm-arm/arch-* directory>
-    Type: <MACH_TYPE_* macro name>
-    Description:
-    <description of your machine>
+  Due to the large number of machines which the ARM port of Linux provides
+  for, we have a method to manage this which ensures that we don't end up
+  duplicating large amounts of code.
 
-  Please follow this format - it is an automated system.  You should
-  receive a reply in short order.
+  We group machine (or platform) support code into machine classes.  A
+  class typically based around one or more system on a chip devices, and
+  acts as a natural container around the actual implementations.  These
+  classes are given directories - arch/arm/mach-<class> and
+  include/asm-arm/arch-<class> - which contain the source files to
+  support the machine class.  This directories also contain any machine
+  specific supporting code.
+
+  For example, the SA1100 class is based upon the SA1100 and SA1110 SoC
+  devices, and contains the code to support the way the on-board and off-
+  board devices are used, or the device is setup, and provides that
+  machine specific "personality."
+
+  This fine-grained machine specific selection is controlled by the machine
+  type ID, which acts both as a run-time and a compile-time code selection
+  method.
+
+  You can register a new machine via the web site at:
+
+    <http://www.arm.linux.org.uk/developer/machines/>
 
 ---
-Russell King (26/01/2001)
+Russell King (15/03/2004)