xref: /openbmc/u-boot/include/linux/bitfield.h (revision e3963c09)
1 /*
2  * Copyright (C) 2014 Felix Fietkau <nbd@nbd.name>
3  * Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@gmail.com>
4  *
5  * This program is free software; you can redistribute it and/or modify
6  * it under the terms of the GNU General Public License version 2
7  * as published by the Free Software Foundation
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  */
14 
15 #ifndef _LINUX_BITFIELD_H
16 #define _LINUX_BITFIELD_H
17 
18 #include <linux/bug.h>
19 
20 /*
21  * Bitfield access macros
22  *
23  * FIELD_{GET,PREP} macros take as first parameter shifted mask
24  * from which they extract the base mask and shift amount.
25  * Mask must be a compilation time constant.
26  *
27  * Example:
28  *
29  *  #define REG_FIELD_A  GENMASK(6, 0)
30  *  #define REG_FIELD_B  BIT(7)
31  *  #define REG_FIELD_C  GENMASK(15, 8)
32  *  #define REG_FIELD_D  GENMASK(31, 16)
33  *
34  * Get:
35  *  a = FIELD_GET(REG_FIELD_A, reg);
36  *  b = FIELD_GET(REG_FIELD_B, reg);
37  *
38  * Set:
39  *  reg = FIELD_PREP(REG_FIELD_A, 1) |
40  *	  FIELD_PREP(REG_FIELD_B, 0) |
41  *	  FIELD_PREP(REG_FIELD_C, c) |
42  *	  FIELD_PREP(REG_FIELD_D, 0x40);
43  *
44  * Modify:
45  *  reg &= ~REG_FIELD_C;
46  *  reg |= FIELD_PREP(REG_FIELD_C, c);
47  */
48 
49 #define __bf_shf(x) (__builtin_ffsll(x) - 1)
50 
51 #define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)			\
52 	({								\
53 		BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),		\
54 				 _pfx "mask is not constant");		\
55 		BUILD_BUG_ON_MSG(!(_mask), _pfx "mask is zero");	\
56 		BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?		\
57 				 ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
58 				 _pfx "value too large for the field"); \
59 		BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull,		\
60 				 _pfx "type of reg too small for mask"); \
61 		__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +			\
62 					      (1ULL << __bf_shf(_mask))); \
63 	})
64 
65 /**
66  * FIELD_FIT() - check if value fits in the field
67  * @_mask: shifted mask defining the field's length and position
68  * @_val:  value to test against the field
69  *
70  * Return: true if @_val can fit inside @_mask, false if @_val is too big.
71  */
72 #define FIELD_FIT(_mask, _val)						\
73 	({								\
74 		__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_FIT: ");	\
75 		!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
76 	})
77 
78 /**
79  * FIELD_PREP() - prepare a bitfield element
80  * @_mask: shifted mask defining the field's length and position
81  * @_val:  value to put in the field
82  *
83  * FIELD_PREP() masks and shifts up the value.  The result should
84  * be combined with other fields of the bitfield using logical OR.
85  */
86 #define FIELD_PREP(_mask, _val)						\
87 	({								\
88 		__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");	\
89 		((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask);	\
90 	})
91 
92 /**
93  * FIELD_GET() - extract a bitfield element
94  * @_mask: shifted mask defining the field's length and position
95  * @_reg:  32bit value of entire bitfield
96  *
97  * FIELD_GET() extracts the field specified by @_mask from the
98  * bitfield passed in as @_reg by masking and shifting it down.
99  */
100 #define FIELD_GET(_mask, _reg)						\
101 	({								\
102 		__BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");	\
103 		(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask));	\
104 	})
105 
106 #endif
107