1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
4 *
5 * Delay routines using pre computed loops_per_jiffy value.
6 *
7 * vineetg: Feb 2012
8 * -Rewrote in "C" to avoid dealing with availability of H/w MPY
9 * -Also reduced the num of MPY operations from 3 to 2
10 *
11 * Amit Bhor: Codito Technologies 2004
12 */
13
14 #ifndef __ASM_ARC_UDELAY_H
15 #define __ASM_ARC_UDELAY_H
16
17 #include <asm-generic/types.h>
18 #include <asm/param.h> /* HZ */
19
20 extern unsigned long loops_per_jiffy;
21
22 static inline void __delay(unsigned long loops)
23 {
24 __asm__ __volatile__(
25 " mov lp_count, %0 \n"
26 " lp 1f \n"
27 " nop \n"
28 "1: \n"
29 :
30 : "r"(loops)
31 : "lp_count");
32 }
33
34 extern void __bad_udelay(void);
35
36 /*
37 * Normal Math for computing loops in "N" usecs
38 * -we have precomputed @loops_per_jiffy
39 * -1 sec has HZ jiffies
40 * loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N)
41 *
42 * Approximate Division by multiplication:
43 * -Mathematically if we multiply and divide a number by same value the
44 * result remains unchanged: In this case, we use 2^32
45 * -> (loops_per_N_usec * 2^32 ) / 2^32
46 * -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32
47 * -> (loops_per_jiffy * HZ * N * 4295) / 2^32
48 *
49 * -Divide by 2^32 is very simply right shift by 32
50 * -We simply need to ensure that the multiply per above eqn happens in
51 * 64-bit precision (if CPU doesn't support it - gcc can emaulate it)
52 */
53
54 static inline void __udelay(unsigned long usecs)
55 {
56 unsigned long loops;
57
58 /* (u64) cast ensures 64 bit MPY - real or emulated
59 * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
60 */
61 loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
62
63 __delay(loops);
64 }
65
66 #define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
67 : __udelay(n)) : __udelay(n))
68
69 #endif /* __ASM_ARC_UDELAY_H */
70
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