MIPS: Alchemy: fix wait function

Only an interrupt can wake the core from 'wait', enable interrupts
locally before executing 'wait'.

[ralf@linux-mips.org: This leave the race between an interrupt that's
setting TIF_NEED_RESCHEd and entering the WAIT status. but at least it's
going to bring Alchemy back from the dead, so I'm going to apply this
patch.]

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/5408/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/idle.c

@@ -93,26 +93,27 @@ static void rm7k_wait_irqoff(void)
 }
 
 /*
- * The Au1xxx wait is available only if using 32khz counter or
- * external timer source, but specifically not CP0 Counter.
- * alchemy/common/time.c may override cpu_wait!
+ * Au1 'wait' is only useful when the 32kHz counter is used as timer,
+ * since coreclock (and the cp0 counter) stops upon executing it. Only an
+ * interrupt can wake it, so they must be enabled before entering idle modes.
  */
 static void au1k_wait(void)
 {
+	unsigned long c0status = read_c0_status() | 1;	/* irqs on */
+
 	__asm__(
 	"	.set	mips3			\n"
 	"	cache	0x14, 0(%0)		\n"
 	"	cache	0x14, 32(%0)		\n"
 	"	sync				\n"
-	"	nop				\n"
+	"	mtc0	%1, $12			\n" /* wr c0status */
 	"	wait				\n"
 	"	nop				\n"
 	"	nop				\n"
 	"	nop				\n"
 	"	nop				\n"
 	"	.set	mips0			\n"
-	: : "r" (au1k_wait));
-	local_irq_enable();
+	: : "r" (au1k_wait), "r" (c0status));
 }
 
 static int __initdata nowait;