linux/bitfield.h: import <linux/bitfield.h> from Linux 4.13

Copied from Linux 4.13.

Commit log of 3e9b3112ec74 of Linux explains well why this header
is useful.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
new file mode 100644 (file)
index 0000000..8b9d6ff
--- /dev/null
+++ b/include/linux/bitfield.h
@@ -0,0 +1,106 @@
+/*
+ * 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_FIT() - check if value fits in the field
+ * @_mask: shifted mask defining the field's length and position
+ * @_val:  value to test against the field
+ *
+ * Return: true if @_val can fit inside @_mask, false if @_val is too big.
+ */
+#define FIELD_FIT(_mask, _val)                                         \
+       ({                                                              \
+               __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_FIT: ");     \
+               !((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_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