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-rw-r--r--kernel/arch/arc/include/asm/delay.h67
1 files changed, 67 insertions, 0 deletions
diff --git a/kernel/arch/arc/include/asm/delay.h b/kernel/arch/arc/include/asm/delay.h
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+++ b/kernel/arch/arc/include/asm/delay.h
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Delay routines using pre computed loops_per_jiffy value.
+ *
+ * vineetg: Feb 2012
+ * -Rewrote in "C" to avoid dealing with availability of H/w MPY
+ * -Also reduced the num of MPY operations from 3 to 2
+ *
+ * Amit Bhor: Codito Technologies 2004
+ */
+
+#ifndef __ASM_ARC_UDELAY_H
+#define __ASM_ARC_UDELAY_H
+
+#include <asm/param.h> /* HZ */
+
+static inline void __delay(unsigned long loops)
+{
+ __asm__ __volatile__(
+ "1: sub.f %0, %0, 1 \n"
+ " jpnz 1b \n"
+ : "+r"(loops)
+ :
+ : "cc");
+}
+
+extern void __bad_udelay(void);
+
+/*
+ * Normal Math for computing loops in "N" usecs
+ * -we have precomputed @loops_per_jiffy
+ * -1 sec has HZ jiffies
+ * loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N)
+ *
+ * Approximate Division by multiplication:
+ * -Mathematically if we multiply and divide a number by same value the
+ * result remains unchanged: In this case, we use 2^32
+ * -> (loops_per_N_usec * 2^32 ) / 2^32
+ * -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32
+ * -> (loops_per_jiffy * HZ * N * 4295) / 2^32
+ *
+ * -Divide by 2^32 is very simply right shift by 32
+ * -We simply need to ensure that the multiply per above eqn happens in
+ * 64-bit precision (if CPU doesn't support it - gcc can emaulate it)
+ */
+
+static inline void __udelay(unsigned long usecs)
+{
+ unsigned long loops;
+
+ /* (u64) cast ensures 64 bit MPY - real or emulated
+ * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
+ */
+ loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
+
+ __delay(loops);
+}
+
+#define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
+ : __udelay(n)) : __udelay(n))
+
+#endif /* __ASM_ARC_UDELAY_H */