sh: Conditionalize gUSA support.

This conditionalizes gUSA support. gUSA is not supported on
SMP configurations, and it's not necessary there anyways due
to having other atomicity options (ie, movli.l/movco.l).

Anything implementing the LL/SC semantics (all SH-4A CPUs)
can switch to userspace atomicity implementations without
requiring gUSA. This is left default-enabled on all UP so
that glibc doesn't break.

Those that know what they are doing can disable this explicitly.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index a8693edd4f43..44982c1dfa23 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -570,6 +570,20 @@ config NR_CPUS
 
 source "kernel/Kconfig.preempt"
 
+config GUSA
+        def_bool y
+        depends on !SMP
+        help
+          This enables support for gUSA (general UserSpace Atomicity).
+          This is the default implementation for both UP and non-ll/sc
+          CPUs, and is used by the libc, amongst others.
+
+          For additional information, design information can be found 
+          in <http://lc.linux.or.jp/lc2002/papers/niibe0919p.pdf>.
+
+          This should only be disabled for special cases where alternate
+          atomicity implementations exist.
+
 endmenu
 
 menu "Boot options"