1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3  * Copyright (C) 2014 Felix Fietkau <nbd@nbd.name>
4  * Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@gmail.com>
5  */
6 
7 #ifndef _LINUX_BITFIELD_H
8 #define _LINUX_BITFIELD_H
9 
10 #include <linux/build_bug.h>
11 #include <asm/byteorder.h>
12 
13 /*
14  * Bitfield access macros
15  *
16  * FIELD_{GET,PREP} macros take as first parameter shifted mask
17  * from which they extract the base mask and shift amount.
18  * Mask must be a compilation time constant.
19  *
20  * Example:
21  *
22  *  #define REG_FIELD_A  GENMASK(6, 0)
23  *  #define REG_FIELD_B  BIT(7)
24  *  #define REG_FIELD_C  GENMASK(15, 8)
25  *  #define REG_FIELD_D  GENMASK(31, 16)
26  *
27  * Get:
28  *  a = FIELD_GET(REG_FIELD_A, reg);
29  *  b = FIELD_GET(REG_FIELD_B, reg);
30  *
31  * Set:
32  *  reg = FIELD_PREP(REG_FIELD_A, 1) |
33  *	  FIELD_PREP(REG_FIELD_B, 0) |
34  *	  FIELD_PREP(REG_FIELD_C, c) |
35  *	  FIELD_PREP(REG_FIELD_D, 0x40);
36  *
37  * Modify:
38  *  reg &= ~REG_FIELD_C;
39  *  reg |= FIELD_PREP(REG_FIELD_C, c);
40  */
41 
42 #define __bf_shf(x) (__builtin_ffsll(x) - 1)
43 
44 #define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)			\
45 	({								\
46 		BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),		\
47 				 _pfx "mask is not constant");		\
48 		BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");	\
49 		BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?		\
50 				 ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
51 				 _pfx "value too large for the field"); \
52 		BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull,		\
53 				 _pfx "type of reg too small for mask"); \
54 		__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +			\
55 					      (1ULL << __bf_shf(_mask))); \
56 	})
57 
58 /**
59  * FIELD_MAX() - produce the maximum value representable by a field
60  * @_mask: shifted mask defining the field's length and position
61  *
62  * FIELD_MAX() returns the maximum value that can be held in the field
63  * specified by @_mask.
64  */
65 #define FIELD_MAX(_mask)						\
66 	({								\
67 		__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: ");	\
68 		(typeof(_mask))((_mask) >> __bf_shf(_mask));		\
69 	})
70 
71 /**
72  * FIELD_FIT() - check if value fits in the field
73  * @_mask: shifted mask defining the field's length and position
74  * @_val:  value to test against the field
75  *
76  * Return: true if @_val can fit inside @_mask, false if @_val is too big.
77  */
78 #define FIELD_FIT(_mask, _val)						\
79 	({								\
80 		__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: ");	\
81 		!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
82 	})
83 
84 /**
85  * FIELD_PREP() - prepare a bitfield element
86  * @_mask: shifted mask defining the field's length and position
87  * @_val:  value to put in the field
88  *
89  * FIELD_PREP() masks and shifts up the value.  The result should
90  * be combined with other fields of the bitfield using logical OR.
91  */
92 #define FIELD_PREP(_mask, _val)						\
93 	({								\
94 		__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");	\
95 		((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask);	\
96 	})
97 
98 /**
99  * FIELD_GET() - extract a bitfield element
100  * @_mask: shifted mask defining the field's length and position
101  * @_reg:  value of entire bitfield
102  *
103  * FIELD_GET() extracts the field specified by @_mask from the
104  * bitfield passed in as @_reg by masking and shifting it down.
105  */
106 #define FIELD_GET(_mask, _reg)						\
107 	({								\
108 		__BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");	\
109 		(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask));	\
110 	})
111 
112 extern void __compiletime_error("value doesn't fit into mask")
113 __field_overflow(void);
114 extern void __compiletime_error("bad bitfield mask")
115 __bad_mask(void);
field_multiplier(u64 field)116 static __always_inline u64 field_multiplier(u64 field)
117 {
118 	if ((field | (field - 1)) & ((field | (field - 1)) + 1))
119 		__bad_mask();
120 	return field & -field;
121 }
field_mask(u64 field)122 static __always_inline u64 field_mask(u64 field)
123 {
124 	return field / field_multiplier(field);
125 }
126 #define field_max(field)	((typeof(field))field_mask(field))
127 #define ____MAKE_OP(type,base,to,from)					\
128 static __always_inline __##type type##_encode_bits(base v, base field)	\
129 {									\
130 	if (__builtin_constant_p(v) && (v & ~field_mask(field)))	\
131 		__field_overflow();					\
132 	return to((v & field_mask(field)) * field_multiplier(field));	\
133 }									\
134 static __always_inline __##type type##_replace_bits(__##type old,	\
135 					base val, base field)		\
136 {									\
137 	return (old & ~to(field)) | type##_encode_bits(val, field);	\
138 }									\
139 static __always_inline void type##p_replace_bits(__##type *p,		\
140 					base val, base field)		\
141 {									\
142 	*p = (*p & ~to(field)) | type##_encode_bits(val, field);	\
143 }									\
144 static __always_inline base type##_get_bits(__##type v, base field)	\
145 {									\
146 	return (from(v) & field)/field_multiplier(field);		\
147 }
148 #define __MAKE_OP(size)							\
149 	____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu)	\
150 	____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu)	\
151 	____MAKE_OP(u##size,u##size,,)
152 ____MAKE_OP(u8,u8,,)
153 __MAKE_OP(16)
154 __MAKE_OP(32)
155 __MAKE_OP(64)
156 #undef __MAKE_OP
157 #undef ____MAKE_OP
158 
159 #endif
160