From 4247d1a9a27b6a23092a2c75e94e0545ad6a3376 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 26 Feb 2013 14:43:02 +0100
Subject: [PATCH] powerpc: use ATB clock, if it's available

The ATB is more precise, but we don't know if it's available.
Check by forking off a process that attempts to use it, if
we die with SIGILL, then we know it's not there.

Based on code from Steven Noonan.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 arch/arch-ppc.h | 57 ++++++++++++++++++++++++++++++++++++++++++++++---
 arch/arch.h     |  2 ++
 2 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/arch/arch-ppc.h b/arch/arch-ppc.h
index e73093df..75176275 100644
--- a/arch/arch-ppc.h
+++ b/arch/arch-ppc.h
@@ -1,6 +1,11 @@
 #ifndef ARCH_PPC_H
 #define ARCH_PPH_H
 
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
 #define FIO_ARCH	(arch_ppc)
 
 #ifndef __NR_ioprio_set
@@ -43,26 +48,72 @@ static inline int arch_ffz(unsigned long bitmask)
 	return  __ilog2(bitmask & -bitmask);
 }
 
+static inline unsigned int mfspr(unsigned int reg)
+{
+	unsigned int val;
+
+	asm volatile("mfspr %0,%1": "=r" (val) : "K" (reg));
+	return val;
+}
+
+#define SPRN_TBRL  0x10C /* Time Base Register Lower */
+#define SPRN_TBRU  0x10D /* Time Base Register Upper */
+#define SPRN_ATBL  0x20E /* Alternate Time Base Lower */
+#define SPRN_ATBU  0x20F /* Alternate Time Base Upper */
+
 static inline unsigned long long get_cpu_clock(void)
 {
 	unsigned int tbl, tbu0, tbu1;
 	unsigned long long ret;
 
 	do {
-		__asm__ __volatile__ ("mftbu %0" : "=r"(tbu0));
-		__asm__ __volatile__ ("mftb %0"  : "=r"(tbl) );
-		__asm__ __volatile__ ("mftbu %0" : "=r"(tbu1));
+		if (arch_flags & ARCH_FLAG_1) {
+			tbu0 = mfspr(SPRN_ATBU);
+			tbl = mfspr(SPRN_ATBL);
+			tbu1 = mfspr(SPRN_ATBU);
+		} else {
+			__asm__ __volatile__("mftbu %0" : "=r"(tbu0));
+			__asm__ __volatile__("mftb %0"  : "=r"(tbl) );
+			__asm__ __volatile__("mftbu %0" : "=r"(tbu1));
+		}
 	} while (tbu0 != tbu1);
 
 	ret = (((unsigned long long)tbu0) << 32) | tbl;
 	return ret;
 }
 
+static void atb_child(void)
+{
+	arch_flags |= ARCH_FLAG_1;
+	get_cpu_clock();
+	_exit(0);
+}
+
+static void atb_clocktest(void)
+{
+	pid_t pid;
+
+	pid = fork();
+	if (!pid)
+		atb_child();
+	else {
+		int status;
+
+		wait(&status);
+		if (!WIFEXITED(status))
+			arch_flags &= ~ARCH_FLAG_1;
+		else
+			arch_flags |= ARCH_FLAG_1;
+	}
+}
+
 #define ARCH_HAVE_INIT
 extern int tsc_reliable;
+
 static inline int arch_init(char *envp[])
 {
 	tsc_reliable = 1;
+	atb_clocktest();
 	return 0;
 }
 
diff --git a/arch/arch.h b/arch/arch.h
index 4165c9f9..31d96d40 100644
--- a/arch/arch.h
+++ b/arch/arch.h
@@ -27,6 +27,8 @@ enum {
 	ARCH_FLAG_4	= 1 << 3,
 };
 
+extern unsigned long arch_flags;
+
 #if defined(__i386__)
 #include "arch-x86.h"
 #elif defined(__x86_64__)
-- 
2.25.1