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>

4 files changed, 18 insertions, 2 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"
diff --git a/arch/sh/kernel/entry-common.S b/arch/sh/kernel/entry-common.S
index b46728027195..e0317ed080c3 100644
--- a/arch/sh/kernel/entry-common.S
+++ b/arch/sh/kernel/entry-common.S
@@ -176,7 +176,7 @@ work_notifysig:
         jmp     @r1
          lds    r0, pr
 work_resched:
-#ifndef CONFIG_PREEMPT
+#if defined(CONFIG_GUSA) && !defined(CONFIG_PREEMPT)
         ! gUSA handling
         mov.l   @(OFF_SP,r15), r0       ! get user space stack pointer
         mov     r0, r1
diff --git a/arch/sh/kernel/process.c b/arch/sh/kernel/process.c
index cd8dae16e940..b4469992d6b2 100644
--- a/arch/sh/kernel/process.c
+++ b/arch/sh/kernel/process.c
@@ -350,7 +350,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
         unlazy_fpu(prev, task_pt_regs(prev));
 #endif
 
-#ifdef CONFIG_PREEMPT
+#if defined(CONFIG_GUSA) && defined(CONFIG_PREEMPT)
         {
                 struct pt_regs *regs;
 
diff --git a/arch/sh/kernel/signal.c b/arch/sh/kernel/signal.c
index 0f657d32ceb9..2f42442cf164 100644
--- a/arch/sh/kernel/signal.c
+++ b/arch/sh/kernel/signal.c
@@ -507,6 +507,7 @@ handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
                                                 ctrl_inw(regs->pc - 4));
                                 break;
                 }
+#ifdef CONFIG_GUSA
         } else {
                 /* gUSA handling */
                 preempt_disable();
@@ -523,6 +524,7 @@ handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
                 }
 
                 preempt_enable_no_resched();
+#endif
         }
 
         /* Set up the stack frame */