powerpc/ftrace: add powerpc timebase as a trace clock source

Add a new powerpc-specific trace clock using the timebase register,
similar to x86-tsc. This gives us
- a fast, monotonic, hardware clock source for trace entries, and
- a clock that can be used to correlate events across cpus as well as across
  hypervisor and guests.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Documentation/trace/ftrace.txt

@@ -346,6 +346,11 @@ of ftrace. Here is a list of some of the key files:
 	  x86-tsc: Architectures may define their own clocks. For
 	  	   example, x86 uses its own TSC cycle clock here.
 
+	  ppc-tb: This uses the powerpc timebase register value.
+		  This is in sync across CPUs and can also be used
+		  to correlate events across hypervisor/guest if
+		  tb_offset is known.
+
 	To set a clock, simply echo the clock name into this file.
 
 	  echo global > trace_clock

arch/powerpc/include/asm/Kbuild

@@ -6,5 +6,4 @@ generic-y += local64.h
 generic-y += mcs_spinlock.h
 generic-y += preempt.h
 generic-y += rwsem.h
-generic-y += trace_clock.h
 generic-y += vtime.h

arch/powerpc/include/asm/trace_clock.h

@@ -0,0 +1,19 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2, as
+ * published by the Free Software Foundation.
+ *
+ * Copyright (C) 2015 Naveen N. Rao, IBM Corporation
+ */
+
+#ifndef _ASM_PPC_TRACE_CLOCK_H
+#define _ASM_PPC_TRACE_CLOCK_H
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+
+extern u64 notrace trace_clock_ppc_tb(void);
+
+#define ARCH_TRACE_CLOCKS { trace_clock_ppc_tb, "ppc-tb", 0 },
+
+#endif  /* _ASM_PPC_TRACE_CLOCK_H */

arch/powerpc/kernel/Makefile

@@ -118,6 +118,7 @@ obj-$(CONFIG_PPC_IO_WORKAROUNDS)	+= io-workarounds.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o
+obj-$(CONFIG_TRACING)		+= trace_clock.o
 
 ifneq ($(CONFIG_PPC_INDIRECT_PIO),y)
 obj-y				+= iomap.o

arch/powerpc/kernel/trace_clock.c

@@ -0,0 +1,15 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2, as
+ * published by the Free Software Foundation.
+ *
+ * Copyright (C) 2015 Naveen N. Rao, IBM Corporation
+ */
+
+#include <asm/trace_clock.h>
+#include <asm/time.h>
+
+u64 notrace trace_clock_ppc_tb(void)
+{
+	return get_tb();
+}