sh: delay slot future proofing via EXPMASK on SH-4A parts.

This implements EXPMASK initialization code for SH-4A parts, where it is
possible to disable compat features that will go away in newer cores.
Presently this includes disabling support for non-nop instructions in the
rte delay slot, as well as a sleep instruction being placed in a delay
slot (neither of which the kernel does any longer). As a result of this,
any future offenders will have illegal slot exceptions generated for
them.

Associative writes for the memory-mapped cache array are still left
enabled, until such a point that special cache operations for SH-4A are
provided to move off of the current (and rather dated) SH-4 versions.

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

arch/sh/kernel/cpu/init.c

@@ -3,7 +3,7 @@
  *
  * CPU init code
  *
- * Copyright (C) 2002 - 2007  Paul Mundt
+ * Copyright (C) 2002 - 2009  Paul Mundt
  * Copyright (C) 2003  Richard Curnow
  *
  * This file is subject to the terms and conditions of the GNU General Public
@@ -62,6 +62,37 @@ static void __init speculative_execution_init(void)
 #define speculative_execution_init()	do { } while (0)
 #endif
 
+#ifdef CONFIG_CPU_SH4A
+#define EXPMASK			0xff2f0004
+#define EXPMASK_RTEDS		(1 << 0)
+#define EXPMASK_BRDSSLP		(1 << 1)
+#define EXPMASK_MMCAW		(1 << 4)
+
+static void __init expmask_init(void)
+{
+	unsigned long expmask = __raw_readl(EXPMASK);
+
+	/*
+	 * Future proofing.
+	 *
+	 * Disable support for slottable sleep instruction
+	 * and non-nop instructions in the rte delay slot.
+	 */
+	expmask &= ~(EXPMASK_RTEDS | EXPMASK_BRDSSLP);
+
+	/*
+	 * Enable associative writes to the memory-mapped cache array
+	 * until the cache flush ops have been rewritten.
+	 */
+	expmask |= EXPMASK_MMCAW;
+
+	__raw_writel(expmask, EXPMASK);
+	ctrl_barrier();
+}
+#else
+#define expmask_init()	do { } while (0)
+#endif
+
 /* 2nd-level cache init */
 void __uses_jump_to_uncached __attribute__ ((weak)) l2_cache_init(void)
 {
@@ -321,4 +352,5 @@ asmlinkage void __init sh_cpu_init(void)
 #endif
 
 	speculative_execution_init();
+	expmask_init();
 }