[PATCH v2] powerpc: re-enable dynticks

[Paul Clarke]

implement arch_irq_work_has_interrupt() for powerpc

Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for 
full dynamic ticks to be enabled, by expecting architectures to 
implement a suitable arch_irq_work_has_interrupt() routine.

Several arches have implemented this routine, including x86 (3010279f) 
and arm (09f6edd4), but powerpc was omitted.

This patch implements this routine for powerpc.

The symptom, at boot (on powerpc arch systems) with "nohz_full=<CPU 
list>" is displayed:
     NO_HZ: Can't run full dynticks because arch doesn't support irq 
work self-IPIs

after this patch:
     NO_HZ: Full dynticks CPUs: <CPU list>.

Tested against 3.19.

v2: changed "return 1" to "return true", per Michael Ellerman

CC: Frederic Weisbecker <fweisbec at gmail.com>
CC: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Signed-off-by: Paul A. Clarke <pc at us.ibm.com>

diff --git a/arch/powerpc/include/asm/irq_work.h 
b/arch/powerpc/include/asm/irq_work.h
new file mode 100644
index 0000000..99cc0aa
--- /dev/null
+++ b/arch/powerpc/include/asm/irq_work.h
@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+	return true;
+}
+
+#endif /* _ASM_IRQ_WORK_H */