MIPS, Perf-events: Work with irq_work

This is the MIPS part of the following commit by Peter Zijlstra:

- e360adbe29241a0194e10e20595360dd7b98a2b3
irq_work: Add generic hardirq context callbacks

Provide a mechanism that allows running code in IRQ context. It is
most useful for NMI code that needs to interact with the rest of the
system -- like wakeup a task to drain buffers.

Perf currently has such a mechanism, so extract that and provide it as
a generic feature, independent of perf so that others may also
benefit.

The IRQ context callback is generated through self-IPIs where
possible, or on architectures like powerpc the decrementer (the
built-in timer facility) is set to generate an interrupt immediately.

Architectures that don't have anything like this get to do with a
callback from the timer tick. These architectures can call
irq_work_run() at the tail of any IRQ handlers that might enqueue such
work (like the perf IRQ handler) to avoid undue latencies in
processing the work.

For MIPSXX, we need to call irq_work_run() at the tail of the perf IRQ
handler as described above.

Reported-by: Wu Zhangjin <[e-mail]>
Acked-by: Peter Zijlstra <[e-mail]>
Acked-by: David Daney <[e-mail]>
Signed-off-by: Deng-Cheng Zhu <[e-mail]>
To: [e-mail]
To: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail],
Patchwork: http://patchwork.linux-mips.org/patch/2011/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/Kconfig

···
 	select HAVE_GENERIC_DMA_COHERENT
 	select HAVE_IDE
 	select HAVE_OPROFILE
+	select HAVE_IRQ_WORK
 	select HAVE_PERF_EVENTS
 	select PERF_USE_VMALLOC
 	select HAVE_ARCH_KGDB

arch/mips/include/asm/perf_event.h

···
 
 #ifndef __MIPS_PERF_EVENT_H__
 #define __MIPS_PERF_EVENT_H__
-
-/*
- * MIPS performance counters do not raise NMI upon overflow, a regular
- * interrupt will be signaled. Hence we can do the pending perf event
- * work at the tail of the irq handler.
- */
-static inline void
-set_perf_event_pending(void)
-{
-}
-
+/* Leave it empty here. The file is required by linux/perf_event.h */
 #endif /* __MIPS_PERF_EVENT_H__ */

arch/mips/kernel/perf_event_mipsxx.c

···
 	 * interrupt, not NMI.
 	 */
 	if (handled == IRQ_HANDLED)
-		perf_event_do_pending();
+		irq_work_run();
 
 #ifdef CONFIG_MIPS_MT_SMP
 	read_unlock(&pmuint_rwlock);