From 659368dde84e22aa3ff10187e05ce202fde8d804 Mon Sep 17 00:00:00 2001
From: Wu Zhangjin <wuzhangjin@gmail.com>
Date: Mon, 1 Feb 2010 18:47:38 +0800
Subject: [PATCH] MIPS: add a common mips_sched_clock()

commit 659368dde84e22aa3ff10187e05ce202fde8d804 in tip.

Because the high resolution sched_clock() for r4k has the same overflow
problem and solution mentioned in "MIPS: Octeon: Use non-overflowing
arithmetic in sched_clock".

    "With typical mult and shift values, the calculation for Octeon's
    sched_clock overflows when using 64-bit arithmetic.  Use 128-bit
    calculations instead."

To reduce the duplication, This patch abstracts the solution into an
inline funciton mips_sched_clock() into arch/mips/include/asm/time.h
from arch/mips/cavium-octeon/csrc-octeon.c.

Two patches for Cavium and R4K will be sent out respectively to use this
common function.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>

diff --git a/arch/mips/include/asm/time.h b/arch/mips/include/asm/time.h
index c7f1bfe..f7bd5ce 100644
--- a/arch/mips/include/asm/time.h
+++ b/arch/mips/include/asm/time.h
@@ -96,4 +96,34 @@ static inline void clockevent_set_clock(struct clock_event_device *cd,
 	clockevents_calc_mult_shift(cd, clock, 4);
 }
 
+static inline unsigned long long mips_sched_clock(struct clocksource *cs, u64 cnt)
+{
+	/* 64-bit arithmatic can overflow, so use 128-bit.  */
+#if (__GNUC__ < 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ <= 3))
+	u64 t1, t2, t3;
+	unsigned long long rv;
+	u64 mult = cs->mult;
+	u64 shift = cs->shift;
+
+	asm (
+		"dmultu\t%[cnt],%[mult]\n\t"
+		"nor\t%[t1],$0,%[shift]\n\t"
+		"mfhi\t%[t2]\n\t"
+		"mflo\t%[t3]\n\t"
+		"dsll\t%[t2],%[t2],1\n\t"
+		"dsrlv\t%[rv],%[t3],%[shift]\n\t"
+		"dsllv\t%[t1],%[t2],%[t1]\n\t"
+		"or\t%[rv],%[t1],%[rv]\n\t"
+		: [rv] "=&r" (rv), [t1] "=&r" (t1), [t2] "=&r" (t2), [t3] "=&r" (t3)
+		: [cnt] "r" (cnt), [mult] "r" (mult), [shift] "r" (shift)
+		: "hi", "lo");
+	return rv;
+#else	/* GCC > 4.3 do it the easy way.  */
+	unsigned int __attribute__((mode(TI))) t = cnt;
+
+	t = (t * cs->mult) >> cs->shift;
+	return (unsigned long long)t;
+#endif
+}
+
 #endif /* _ASM_TIME_H */
-- 
1.7.1.1