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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 | ||
22 | static inline void __delay(unsigned long loops) | |
23 | { | |
24 | __asm__ __volatile__( | |
8922bc30 VG |
25 | " lp 1f \n" |
26 | " nop \n" | |
27 | "1: \n" | |
28 | : "+l"(loops)); | |
d8005e6b VG |
29 | } |
30 | ||
31 | extern 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 | ||
51 | static inline void __udelay(unsigned long usecs) | |
52 | { | |
53 | unsigned long loops; | |
54 | ||
7efd0da2 | 55 | /* (u64) cast ensures 64 bit MPY - real or emulated |
d8005e6b VG |
56 | * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops |
57 | */ | |
7efd0da2 | 58 | loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32; |
d8005e6b VG |
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 */ |