[PATCHv2] 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.

2012-02-17  Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>

	* sysdeps/unix/sysv/linux/powerpc/sys/user.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/user.h         |   38 +++++++++++++++++++-
 sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c |   37 +++++++++++++++++++
 3 files changed, 76 insertions(+), 1 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 55311a4..a2ab09a 100644
--- a/sysdeps/unix/sysv/linux/powerpc/Makefile
+++ b/sysdeps/unix/sysv/linux/powerpc/Makefile
@@ -15,3 +15,5 @@ endif
 ifeq ($(subdir),elf)
 sysdep_routines += dl-vdso
 endif
+
+tests += test-gettimebase
diff --git a/sysdeps/unix/sysv/linux/powerpc/sys/user.h b/sysdeps/unix/sysv/linux/powerpc/sys/user.h
index 5fa3745..d26c70b 100644
--- a/sysdeps/unix/sysv/linux/powerpc/sys/user.h
+++ b/sysdeps/unix/sysv/linux/powerpc/sys/user.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 1998 Free Software Foundation, Inc.
+/* Copyright (C) 1998, 2012 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -36,4 +36,40 @@ struct user {
 	char		u_comm[32];		/* user command name */
 };
 
+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 %[tb], 268\n"
+		    : [tb]"=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 %[tbu]\n"
+		    "mftbl %[tbl]\n"
+		    "mftbu %[tmp]\n"
+		    "cmpw %[tbu], %[tmp]\n"
+		    "bne- 0b\n"
+		    : [tbu]"=r" (__tbu), [tbl]"=r" (__tbl), [tmp]"=r" (__tmp)
+		    : );
+  return (( (__ppc_timebase) __tbu << 32) | __tbl);
+}
+#endif  /* not __powerpc64__ */
+
 #endif  /* sys/user.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..90b207b
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c
@@ -0,0 +1,37 @@
+/* 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_GETTIMEBASE() is compatible with the current processor.
+   In case of failure it may indicate a future Power ISA or a binutils
+   change.  */
+
+#include <stdio.h>
+
+#include <sys/user.h>
+
+static int
+do_test(void)
+{
+  __ppc_timebase tb = __ppc_get_timebase ();
+  printf ("Time Base = %llx\n", tb);
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
-- 
1.7.4.4