metag: move irq enable out of irqflags.h on SMP

The SMP version of arch_local_irq_enable() uses preempt_disable(), but
<asm/irqflags.h> doesn't include <linux/preempt.h> causing the following
errors on SMP when pstore/ftrace is enabled (caught by buildbot smp
allyesconfig):

In file included from include/linux/irqflags.h:15,
                 from fs/pstore/ftrace.c:16:
arch/metag/include/asm/irqflags.h: In function 'arch_local_irq_enable':
arch/metag/include/asm/irqflags.h:84: error: implicit declaration of function 'preempt_disable'
arch/metag/include/asm/irqflags.h:86: error: implicit declaration of function 'preempt_enable_no_resched'

However <linux/preempt.h> cannot be easily included from
<asm/irqflags.h> as it can cause circular include dependencies in the
!SMP case, and potentially in the SMP case in the future. Therefore move
the SMP implementation of arch_local_irq_enable() into traps.c and use
an inline version of get_trigger_mask() which is also defined in traps.c
for SMP.

This adds an extra layer of function call / stack push when
preempt_disable needs to call other functions, however in the
non-preemptive SMP case it should be about as fast, as it was already
calling the get_trigger_mask() function which is now used inline.
Signed-off-by: James Hogan <james.hogan@imgtec.com>

arch/metag/include/asm/irqflags.h

@@ -78,16 +78,15 @@ static inline void arch_local_irq_disable(void)
 	asm volatile("MOV TXMASKI,%0\n" : : "r" (flags) : "memory");
 }
 
-static inline void arch_local_irq_enable(void)
-{
 #ifdef CONFIG_SMP
-	preempt_disable();
-	arch_local_irq_restore(get_trigger_mask());
-	preempt_enable_no_resched();
+/* Avoid circular include dependencies through <linux/preempt.h> */
+void arch_local_irq_enable(void);
 #else
+static inline void arch_local_irq_enable(void)
+{
 	arch_local_irq_restore(get_trigger_mask());
-#endif
 }
+#endif
 
 #endif /* (__ASSEMBLY__) */
 

arch/metag/kernel/traps.c

@@ -15,6 +15,7 @@
 #include <linux/types.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
+#include <linux/preempt.h>
 #include <linux/ptrace.h>
 #include <linux/module.h>
 #include <linux/kallsyms.h>
@@ -776,17 +777,30 @@ int traps_restore_context(void)
 #endif
 
 #ifdef CONFIG_SMP
-unsigned int get_trigger_mask(void)
+static inline unsigned int _get_trigger_mask(void)
 {
 	unsigned long cpu = smp_processor_id();
 	return per_cpu(trigger_mask, cpu);
 }
 
+unsigned int get_trigger_mask(void)
+{
+	return _get_trigger_mask();
+}
+
 static void set_trigger_mask(unsigned int mask)
 {
 	unsigned long cpu = smp_processor_id();
 	per_cpu(trigger_mask, cpu) = mask;
 }
+
+void arch_local_irq_enable(void)
+{
+	preempt_disable();
+	arch_local_irq_restore(_get_trigger_mask());
+	preempt_enable_no_resched();
+}
+EXPORT_SYMBOL(arch_local_irq_enable);
 #else
 static void set_trigger_mask(unsigned int mask)
 {