LinuxKPI: add a bitfield.h implementation.

This code was iteratively implemented during the work on various WiFi
drivers -- from individual functions to a macro-created implementations
for the various bit sized needed (and then extended to more for
comepleteness). Some of the bit combinations do not seem to make sense
so are left out.

The __bf_shf(x) was obtained from D26681 [1].

Requested by:		manu [1]
Reviewed by:		hselasky, manu
MFC after:		1 week
Sponsored by:		The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D26708

sys/compat/linuxkpi/common/include/linux/bitfield.h

@@ -0,0 +1,105 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2020 The FreeBSD Foundation
+ *
+ * This software was developed by Björn Zeeb under sponsorship from
+ * the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef	_LINUX_BITFIELD_H
+#define	_LINUX_BITFIELD_H
+
+#include <linux/types.h>
+#include <asm/byteorder.h>
+
+/* Use largest possible type. */
+static inline uint64_t ___lsb(uint64_t f) { return (f & -f); }
+static inline uint64_t ___bitmask(uint64_t f) { return (f / ___lsb(f)); }
+
+#define	_uX_get_bits(_n)						\
+	static __inline uint ## _n ## _t				\
+	u ## _n ## _get_bits(uint ## _n ## _t v, uint ## _n ## _t f)	\
+	{								\
+		return ((v & f) / ___lsb(f));				\
+	}
+
+_uX_get_bits(64)
+_uX_get_bits(32)
+_uX_get_bits(16)
+_uX_get_bits(8)
+
+#define	_leX_get_bits(_n)						\
+	static __inline uint ## _n ## _t				\
+	le ## _n ## _get_bits(__le ## _n v, uint ## _n ## _t f)		\
+	{								\
+		return ((le ## _n ## _to_cpu(v) & f) / ___lsb(f));	\
+	}
+
+_leX_get_bits(64)
+_leX_get_bits(32)
+_leX_get_bits(16)
+
+#define	_uX_encode_bits(_n)						\
+	static __inline uint ## _n ## _t				\
+	u ## _n ## _encode_bits(uint ## _n ## _t v, uint ## _n ## _t f)	\
+	{								\
+		return ((v & ___bitmask(f)) * ___lsb(f));		\
+	}
+
+_uX_encode_bits(64)
+_uX_encode_bits(32)
+_uX_encode_bits(16)
+_uX_encode_bits(8)
+
+#define	_leX_encode_bits(_n)						\
+	static __inline uint ## _n ## _t				\
+	le ## _n ## _encode_bits(__le ## _n v, uint ## _n ## _t f)\
+	{								\
+		return (cpu_to_le ## _n((v & ___bitmask(f)) * ___lsb(f))); \
+	}
+
+_leX_encode_bits(64)
+_leX_encode_bits(32)
+_leX_encode_bits(16)
+
+static __inline void
+le32p_replace_bits(uint32_t *p, uint32_t v, uint32_t f)
+{
+
+	*p = (*p & ~(cpu_to_le32(v))) | le32_encode_bits(v, f);
+	return;
+}
+
+#define	__bf_shf(x)	(__builtin_ffsll(x) - 1)
+
+#define	FIELD_PREP(_mask, _value)					\
+	(((typeof(_mask))(_value) << __bf_shf(_mask)) & (_mask))
+
+#define	FIELD_GET(_mask, _value)					\
+	((typeof(_mask))(((_value) & (_mask)) >> __bf_shf(_mask)))
+
+#endif	/* _LINUX_BITFIELD_H */