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Diffstat (limited to 'include/linux/bitfield.h')
| -rw-r--r-- | include/linux/bitfield.h | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h new file mode 100644 index 000000000000..f6505d83069d --- /dev/null +++ b/include/linux/bitfield.h @@ -0,0 +1,93 @@ +/* + * Copyright (C) 2014 Felix Fietkau <nbd@nbd.name> + * Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@gmail.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + */ + +#ifndef _LINUX_BITFIELD_H +#define _LINUX_BITFIELD_H + +#include <linux/bug.h> + +/* + * Bitfield access macros + * + * FIELD_{GET,PREP} macros take as first parameter shifted mask + * from which they extract the base mask and shift amount. + * Mask must be a compilation time constant. + * + * Example: + * + * #define REG_FIELD_A GENMASK(6, 0) + * #define REG_FIELD_B BIT(7) + * #define REG_FIELD_C GENMASK(15, 8) + * #define REG_FIELD_D GENMASK(31, 16) + * + * Get: + * a = FIELD_GET(REG_FIELD_A, reg); + * b = FIELD_GET(REG_FIELD_B, reg); + * + * Set: + * reg = FIELD_PREP(REG_FIELD_A, 1) | + * FIELD_PREP(REG_FIELD_B, 0) | + * FIELD_PREP(REG_FIELD_C, c) | + * FIELD_PREP(REG_FIELD_D, 0x40); + * + * Modify: + * reg &= ~REG_FIELD_C; + * reg |= FIELD_PREP(REG_FIELD_C, c); + */ + +#define __bf_shf(x) (__builtin_ffsll(x) - 1) + +#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx) \ + ({ \ + BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \ + _pfx "mask is not constant"); \ + BUILD_BUG_ON_MSG(!(_mask), _pfx "mask is zero"); \ + BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \ + ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \ + _pfx "value too large for the field"); \ + BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull, \ + _pfx "type of reg too small for mask"); \ + __BUILD_BUG_ON_NOT_POWER_OF_2((_mask) + \ + (1ULL << __bf_shf(_mask))); \ + }) + +/** + * FIELD_PREP() - prepare a bitfield element + * @_mask: shifted mask defining the field's length and position + * @_val: value to put in the field + * + * FIELD_PREP() masks and shifts up the value. The result should + * be combined with other fields of the bitfield using logical OR. + */ +#define FIELD_PREP(_mask, _val) \ + ({ \ + __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \ + ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \ + }) + +/** + * FIELD_GET() - extract a bitfield element + * @_mask: shifted mask defining the field's length and position + * @_reg: 32bit value of entire bitfield + * + * FIELD_GET() extracts the field specified by @_mask from the + * bitfield passed in as @_reg by masking and shifting it down. + */ +#define FIELD_GET(_mask, _reg) \ + ({ \ + __BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: "); \ + (typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask)); \ + }) + +#endif |