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d2912cb1 | 1 | /* SPDX-License-Identifier: GPL-2.0-only */ |
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2 | /* |
3 | * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) | |
4 | * | |
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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 | ||
2423665e | 17 | #include <asm-generic/types.h> |
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18 | #include <asm/param.h> /* HZ */ |
19 | ||
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20 | extern unsigned long loops_per_jiffy; |
21 | ||
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22 | static inline void __delay(unsigned long loops) |
23 | { | |
24 | __asm__ __volatile__( | |
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25 | " mov lp_count, %0 \n" |
26 | " lp 1f \n" | |
27 | " nop \n" | |
28 | "1: \n" | |
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29 | : |
30 | : "r"(loops) | |
31 | : "lp_count"); | |
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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 | ||
7efd0da2 | 58 | /* (u64) cast ensures 64 bit MPY - real or emulated |
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59 | * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops |
60 | */ | |
7efd0da2 | 61 | loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32; |
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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 */ |