include/bitfield.h

   1 /*
   2  * Copyright 2013 Broadcom Corporation.
   3  *
   4  * SPDX-License-Identifier:      GPL-2.0+
   5  */
   6
   7 /*
   8  * Bitfield operations
   9  *
  10  * These are generic bitfield operations which allow manipulation of variable
  11  * width bitfields within a word. One use of this would be to use data tables
  12  * to determine how to reprogram fields within R/W hardware registers.
  13  *
  14  * Example:
  15  *
  16  *            old_reg_val
  17  * +--------+----+---+--+-----+----------+
  18  * |        |    |   |  | old |          |
  19  * +--------+----+---+--+-----+----------+
  20  *
  21  *            new_reg_val
  22  * +--------+----+---+--+-----+----------+
  23  * |        |    |   |  | new |          |
  24  * +--------+----+---+--+-----+----------+
  25  *
  26  * mask = bitfield_mask(10, 5);
  27  * old = bitfield_extract(old_reg_val, 10, 5);
  28  * new_reg_val = bitfield_replace(old_reg_val, 10, 5, new);
  29  *
  30  * The numbers 10 and 5 could for example come from data
  31  * tables which describe all bitfields in all registers.
  32  */
  33
  34 #include <linux/types.h>
  35
  36 /* Produces a mask of set bits covering a range of a uint value */
  37 static inline uint bitfield_mask(uint shift, uint width)
  38 {
  39         return ((1 << width) - 1) << shift;
  40 }
  41
  42 /* Extract the value of a bitfield found within a given register value */
  43 static inline uint bitfield_extract(uint reg_val, uint shift, uint width)
  44 {
  45         return (reg_val & bitfield_mask(shift, width)) >> shift;
  46 }
  47
  48 /*
  49  * Replace the value of a bitfield found within a given register value
  50  * Returns the newly modified uint value with the replaced field.
  51  */
  52 static inline uint bitfield_replace(uint reg_val, uint shift, uint width,
  53                                     uint bitfield_val)
  54 {
  55         uint mask = bitfield_mask(shift, width);
  56
  57         return (reg_val & ~mask) | (bitfield_val << shift);
  58 }