[src/trunk]: src/sys/arch/arm/include Back out 1.12 and include a comment as ...

[matt <matt%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/76354b6cbaab
branches:  trunk
changeset: 781714:76354b6cbaab
user:      matt <matt%NetBSD.org@localhost>
date:      Tue Sep 25 05:24:00 2012 +0000

description:
Back out 1.12 and include a comment as to why.

diffstat:

 sys/arch/arm/include/mutex.h |  9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diffs (26 lines):

diff -r 933708f909fa -r 76354b6cbaab sys/arch/arm/include/mutex.h
--- a/sys/arch/arm/include/mutex.h      Mon Sep 24 23:13:36 2012 +0000
+++ b/sys/arch/arm/include/mutex.h      Tue Sep 25 05:24:00 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: mutex.h,v 1.12 2012/08/31 23:56:15 matt Exp $  */
+/*     $NetBSD: mutex.h,v 1.13 2012/09/25 05:24:00 matt Exp $  */
 
 /*-
  * Copyright (c) 2002, 2007 The NetBSD Foundation, Inc.
@@ -61,10 +61,15 @@
 
                /* Spin mutex */
                struct {
+                       /*
+                        * Since the low bit of mtax_owner is used to flag this
+                        * mutex as a spin mutex, we can't use the first byte
+                        * or the last byte to store the ipl or lock values.
+                        */
                        volatile uint8_t        mtxs_dummy;
                        ipl_cookie_t            mtxs_ipl;
+                       __cpu_simple_lock_t     mtxs_lock;
                        volatile uint8_t        mtxs_unused;
-                       __cpu_simple_lock_t     mtxs_lock;
                } s;
        } u;
 };