[PATCH 2/2] PowerPC - Add a faster way to read the Time Base register

[Tulio Magno Quites Machado Filho <tuliom at linux dot vnet dot ibm dot com>]

Add function __ppc_get_timebase() to directly read the Time Base register.
This is required for applications that measure time at high frequencies
with high precision that can't afford a syscall.

2012-03-06  Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>

	* sysdeps/unix/sysv/linux/powerpc/sys/platform.h (__ppc_get_timebase):
	New function definition.
	* sysdeps/unix/sysv/linux/powerpc/Makefile (tests): Add
	test-gettimebase.
	* sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c: Test for
	__ppc_get_timebase() to catch future ISA opcode/insn changes.
---
 sysdeps/unix/sysv/linux/powerpc/Makefile           |    2 +
 sysdeps/unix/sysv/linux/powerpc/sys/platform.h     |   35 +++++++++++++++
 sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c |   47 ++++++++++++++++++++
 3 files changed, 84 insertions(+), 0 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c

diff --git a/sysdeps/unix/sysv/linux/powerpc/Makefile b/sysdeps/unix/sysv/linux/powerpc/Makefile
index c947362..d0b6a1d 100644
--- a/sysdeps/unix/sysv/linux/powerpc/Makefile
+++ b/sysdeps/unix/sysv/linux/powerpc/Makefile
@@ -17,3 +17,5 @@ sysdep_routines += dl-vdso
 endif
 
 sysdep_headers += sys/platform.h
+
+tests += test-gettimebase
diff --git a/sysdeps/unix/sysv/linux/powerpc/sys/platform.h b/sysdeps/unix/sysv/linux/powerpc/sys/platform.h
index 9d1af58..c54d669 100644
--- a/sysdeps/unix/sysv/linux/powerpc/sys/platform.h
+++ b/sysdeps/unix/sysv/linux/powerpc/sys/platform.h
@@ -19,5 +19,40 @@
 
 #define _SYS_PLATFORM_H	1
 
+typedef unsigned long long int __ppc_timebase;
+
+/* Read the Time Base Register
+   The Time Base Register is a 64-bit register that stores a monotonically
+   incremented value updated at a system dependent frequency that may be
+   different of processor frequency.
+   More information in Power ISA 2.06b - Book II - Section 5.2   */
+#ifdef __powerpc64__
+static inline __ppc_timebase
+__ppc_get_timebase (void)
+{
+  __ppc_timebase __tb;
+  __asm__ volatile (
+		    "mfspr %0, 268\n"
+		    : "=r" (__tb)
+		    : );
+  return __tb;
+}
+#else  /* not __powerpc64__ */
+static inline __ppc_timebase
+__ppc_get_timebase (void)
+{
+  register unsigned long __tbu, __tbl, __tmp; \
+  __asm__ volatile (
+		    "0:\n"
+		    "mftbu %0\n"
+		    "mftbl %1\n"
+		    "mftbu %2\n"
+		    "cmpw %0, %2\n"
+		    "bne- 0b\n"
+		    : "=r" (__tbu), "=r" (__tbl), "=r" (__tmp)
+		    : );
+  return (( (__ppc_timebase) __tbu << 32) | __tbl);
+}
+#endif  /* not __powerpc64__ */
 
 #endif  /* sys/platform.h */
diff --git a/sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c b/sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c
new file mode 100644
index 0000000..15308da
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c
@@ -0,0 +1,47 @@
+/* Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Tulio Magno Quites Machado <tuliom@linux.vnet.ibm.com>, 2012.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+/* Test if __ppc_get_timebase() is compatible with the current processor and if
+   it's changing between reads.
+   In case of a read failure it may indicate a future Power ISA or a binutils
+   change.  */
+
+#include <stdio.h>
+
+#include <sys/platform.h>
+
+static int
+do_test(void)
+{
+  __ppc_timebase t1, t2, t3;
+  t1 = __ppc_get_timebase ();
+  printf ("Time Base = %llx\n", t1);
+  t2 = __ppc_get_timebase ();
+  printf ("Time Base = %llx\n", t2);
+  t3 = __ppc_get_timebase ();
+  printf ("Time Base = %llx\n", t3);
+  if ((t1 != t2) && (t1 != t3) && (t2 != t3))
+    return 0;
+
+  printf ("Fail: timebase reads should always be different.");
+  return 1;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
-- 
1.7.4.4