xtensa: implement counting and sampling perf events

Xtensa Performance Monitor Module has up to 8 32 bit wide performance
counters. Each counter may be enabled independently and can count any
single type of hardware performance events. Event counting may be enabled
and disabled globally (per PMM).
Each counter has status register with bits indicating if the counter has
been overflown and may be programmed to raise profiling IRQ on overflow.
This IRQ is used to rewind counters and allow for counting more than 2^32
samples for counting events and to report samples for sampling events.

For more details see Tensilica Debug User's Guide, chapter 8
"Performance monitor module".

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/Kconfig

@@ -128,6 +128,16 @@ config XTENSA_VARIANT_MMU
 	  Build a Conventional Kernel with full MMU support,
 	  ie: it supports a TLB with auto-loading, page protection.
 
+config XTENSA_VARIANT_HAVE_PERF_EVENTS
+	bool "Core variant has Performance Monitor Module"
+	depends on XTENSA_VARIANT_CUSTOM
+	default n
+	help
+	  Enable if core variant has Performance Monitor Module with
+	  External Registers Interface.
+
+	  If unsure, say N.
+
 config XTENSA_UNALIGNED_USER
 	bool "Unaligned memory access in use space"
 	help

arch/xtensa/kernel/Makefile

@@ -13,6 +13,7 @@ obj-$(CONFIG_PCI) += pci.o
 obj-$(CONFIG_MODULES) += xtensa_ksyms.o module.o
 obj-$(CONFIG_FUNCTION_TRACER) += mcount.o
 obj-$(CONFIG_SMP) += smp.o mxhead.o
+obj-$(CONFIG_XTENSA_VARIANT_HAVE_PERF_EVENTS) += perf_event.o
 
 AFLAGS_head.o += -mtext-section-literals