arm64: Support arch_irq_work_raise() via self IPIs

Support for arch_irq_work_raise() was missing from
arm64 (a prerequisite for FULL_NOHZ).

This patch is based on the arm32 patch ARM 7872/1.

commit bf18525fd793101df42a1344ecc48b49b62e48c9
Author: Stephen Boyd <[e-mail]>
Date: Tue Oct 29 20:32:56 2013 +0100

ARM: 7872/1: Support arch_irq_work_raise() via self IPIs

By default, IRQ work is run from the tick interrupt (see
irq_work_run() in update_process_times()). When we're in full
NOHZ mode, restarting the tick requires the use of IRQ work and
if the only place we run IRQ work is in the tick interrupt we
have an unbreakable cycle. Implement arch_irq_work_raise() via
self IPIs to break this cycle and get the tick started again.
Note that we implement this via IPIs which are only available on
SMP builds. This shouldn't be a problem because full NOHZ is only
supported on SMP builds anyway.

Signed-off-by: Stephen Boyd <[e-mail]>
Reviewed-by: Kevin Hilman <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

Signed-off-by: Larry Bassel <[e-mail]>
Reviewed-by: Kevin Hilman <[e-mail]>
Signed-off-by: Catalin Marinas <[e-mail]>

arch/arm64/include/asm/hardirq.h

···
 #include <linux/threads.h>
 #include <asm/irq.h>
 
-#define NR_IPI	5
+#define NR_IPI	6
 
 typedef struct {
 	unsigned int __softirq_pending;

arch/arm64/kernel/smp.c

···
 #include <linux/clockchips.h>
 #include <linux/completion.h>
 #include <linux/of.h>
+#include <linux/irq_work.h>
 
 #include <asm/atomic.h>
 #include <asm/cacheflush.h>
···
 	IPI_CALL_FUNC_SINGLE,
 	IPI_CPU_STOP,
 	IPI_TIMER,
+	IPI_IRQ_WORK,
 };
 
 /*
···
 	smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC_SINGLE);
 }
 
+#ifdef CONFIG_IRQ_WORK
+void arch_irq_work_raise(void)
+{
+	if (smp_cross_call)
+		smp_cross_call(cpumask_of(smp_processor_id()), IPI_IRQ_WORK);
+}
+#endif
+
 static const char *ipi_types[NR_IPI] = {
 #define S(x,s)	[x - IPI_RESCHEDULE] = s
 	S(IPI_RESCHEDULE, "Rescheduling interrupts"),
···
 	S(IPI_CALL_FUNC_SINGLE, "Single function call interrupts"),
 	S(IPI_CPU_STOP, "CPU stop interrupts"),
 	S(IPI_TIMER, "Timer broadcast interrupts"),
+	S(IPI_IRQ_WORK, "IRQ work interrupts"),
 };
 
 void show_ipi_list(struct seq_file *p, int prec)
···
 	case IPI_TIMER:
 		irq_enter();
 		tick_receive_broadcast();
+		irq_exit();
+		break;
+#endif
+
+#ifdef CONFIG_IRQ_WORK
+	case IPI_IRQ_WORK:
+		irq_enter();
+		irq_work_run();
 		irq_exit();
 		break;
 #endif