1/*
 2 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 3 *
 4 * This program is free software; you can redistribute it and/or modify
 5 * it under the terms of the GNU General Public License version 2 as
 6 * published by the Free Software Foundation.
 7 *
 8 * Delay routines using pre computed loops_per_jiffy value.
 9 *
10 * vineetg: Feb 2012
11 *  -Rewrote in "C" to avoid dealing with availability of H/w MPY
12 *  -Also reduced the num of MPY operations from 3 to 2
13 *
14 * Amit Bhor: Codito Technologies 2004
15 */
16
17#ifndef __ASM_ARC_UDELAY_H
18#define __ASM_ARC_UDELAY_H
19
20#include <asm/param.h>		/* HZ */
21
22static inline void __delay(unsigned long loops)
23{
24	__asm__ __volatile__(
25	"	lp  1f	\n"
26	"	nop	\n"
27	"1:		\n"
28	: "+l"(loops));
29}
30
31extern void __bad_udelay(void);
32
33/*
34 * Normal Math for computing loops in "N" usecs
35 *  -we have precomputed @loops_per_jiffy
36 *  -1 sec has HZ jiffies
37 * loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N)
38 *
39 * Approximate Division by multiplication:
40 *  -Mathematically if we multiply and divide a number by same value the
41 *   result remains unchanged:  In this case, we use 2^32
42 *  -> (loops_per_N_usec * 2^32 ) / 2^32
43 *  -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32
44 *  -> (loops_per_jiffy * HZ * N * 4295) / 2^32
45 *
46 *  -Divide by 2^32 is very simply right shift by 32
47 *  -We simply need to ensure that the multiply per above eqn happens in
48 *   64-bit precision (if CPU doesn't support it - gcc can emaulate it)
49 */
50
51static inline void __udelay(unsigned long usecs)
52{
53	unsigned long loops;
54
55	/* (u64) cast ensures 64 bit MPY - real or emulated
56	 * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
57	 */
58	loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
59
60	__delay(loops);
61}
62
63#define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
64				: __udelay(n)) : __udelay(n))
65
66#endif /* __ASM_ARC_UDELAY_H */