x86/UV: Add uvtrace support

This patch adds support for the uvtrace module by providing a
skeleton call to the registered trace function.  It also
provides another separate 'NMI' tracer that is triggered by the
system wide 'power nmi' command.

Signed-off-by: Mike Travis <travis@sgi.com>
Reviewed-by: Dimitri Sivanich <sivanich@sgi.com>
Reviewed-by: Hedi Berriche <hedi@sgi.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Jason Wessel <jason.wessel@windriver.com>
Link: http://lkml.kernel.org/r/20130923212501.185052551@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/platform/uv/uv_nmi.c

@@ -1,5 +1,5 @@
 /*
- * SGI NMI support routines
+ * SGI NMI/TRACE support routines
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -36,6 +36,13 @@
 #include <asm/uv/uv_hub.h>
 #include <asm/uv/uv_mmrs.h>
 
+void (*uv_trace_func)(const char *f, const int l, const char *fmt, ...);
+EXPORT_SYMBOL(uv_trace_func);
+
+void (*uv_trace_nmi_func)(unsigned int reason, struct pt_regs *regs);
+EXPORT_SYMBOL(uv_trace_nmi_func);
+
+
 /*
  * UV handler for NMI
  *
@@ -551,6 +558,10 @@ int uv_handle_nmi(unsigned int reason, struct pt_regs *regs)
 		return NMI_DONE;
 	}
 
+	/* Call possible NMI trace function */
+	if (unlikely(uv_trace_nmi_func))
+		(uv_trace_nmi_func)(reason, regs);
+
 	/* Indicate we are the first CPU into the NMI handler */
 	master = (atomic_read(&uv_nmi_cpu) == cpu);