sh: GUSA atomic rollback support.

This implements kernel-level atomic rollback built on top of gUSA,
as an alternative non-IRQ based atomicity method. This is generally
a faster method for platforms that are lacking the LL/SC pairs that
SH-4A and later use, and is only supportable on legacy cores.

Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 11 insertions, 1 deletions

diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 2dc3b177193c..f645f8416f1c 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -692,7 +692,7 @@ source "kernel/Kconfig.preempt"
 
 config GUSA
         def_bool y
-        depends on !SMP
+        depends on !SMP && SUPERH32
         help
           This enables support for gUSA (general UserSpace Atomicity).
           This is the default implementation for both UP and non-ll/sc
@@ -704,6 +704,16 @@ config GUSA
           This should only be disabled for special cases where alternate
           atomicity implementations exist.
 
+config GUSA_RB
+        bool "Implement atomic operations by roll-back (gRB) (EXPERIMENTAL)"
+        depends on GUSA && CPU_SH3 || (CPU_SH4 && !CPU_SH4A)
+        help
+          Enabling this option will allow the kernel to implement some
+          atomic operations using a software implemention of load-locked/
+          store-conditional (LLSC). On machines which do not have hardware
+          LLSC, this should be more efficient than the other alternative of
+          disabling insterrupts around the atomic sequence.
+
 endmenu
 
 menu "Boot options"