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_PREP() - prepare a bitfield element
67 * @_mask: shifted mask defining the field's length and position
68 * @_val:  value to put in the field
69 *
70 * FIELD_PREP() masks and shifts up the value.  The result should
71 * be combined with other fields of the bitfield using logical OR.
72 */
73#define FIELD_PREP(_mask, _val)						\
74	({								\
75		__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");	\
76		((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask);	\
77	})
78
79/**
80 * FIELD_GET() - extract a bitfield element
81 * @_mask: shifted mask defining the field's length and position
82 * @_reg:  32bit value of entire bitfield
83 *
84 * FIELD_GET() extracts the field specified by @_mask from the
85 * bitfield passed in as @_reg by masking and shifting it down.
86 */
87#define FIELD_GET(_mask, _reg)						\
88	({								\
89		__BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");	\
90		(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask));	\
91	})
92
93#endif