PM: Make PM_TRACE more architecture independent

When trying to debug a suspend failure I started implementing
PM_TRACE for powerpc. I then noticed that I'm debugging a suspend
failure and so PM_TRACE isn't useful at all, but thought that
nonetheless this could be useful in the future.

Basically, to support PM_TRACE, you add a Kconfig option that
selects PM_TRACE and provides the infrastructure as per the
help text of PM_TRACE.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/base/power/Makefile

@@ -1,6 +1,6 @@
 obj-$(CONFIG_PM)	+= sysfs.o
 obj-$(CONFIG_PM_SLEEP)	+= main.o
-obj-$(CONFIG_PM_TRACE)	+= trace.o
+obj-$(CONFIG_PM_TRACE_RTC)	+= trace.o
 
 ccflags-$(CONFIG_DEBUG_DRIVER) := -DDEBUG
 ccflags-$(CONFIG_PM_VERBOSE)   += -DDEBUG

kernel/power/Kconfig

@@ -44,9 +44,30 @@ config PM_VERBOSE
 	---help---
 	This option enables verbose messages from the Power Management code.
 
+config CAN_PM_TRACE
+	def_bool y
+	depends on PM_DEBUG && PM_SLEEP && EXPERIMENTAL
+
 config PM_TRACE
+	bool
+	help
+	  This enables code to save the last PM event point across
+	  reboot. The architecture needs to support this, x86 for
+	  example does by saving things in the RTC, see below.
+
+	  The architecture specific code must provide the extern
+	  functions from <linux/resume-trace.h> as well as the
+	  <asm/resume-trace.h> header with a TRACE_RESUME() macro.
+
+	  The way the information is presented is architecture-
+	  dependent, x86 will print the information during a
+	  late_initcall.
+
+config PM_TRACE_RTC
 	bool "Suspend/resume event tracing"
-	depends on PM_DEBUG && X86 && PM_SLEEP && EXPERIMENTAL
+	depends on CAN_PM_TRACE
+	depends on X86
+	select PM_TRACE
 	default n
 	---help---
 	This enables some cheesy code to save the last PM event point in the