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  * or
  31  *
  32  * mask = bitfield_mask(10, 5);
  33  * old = bitfield_extract_by_mask(old_reg_val, mask);
  34  * new_reg_val = bitfield_replace_by_mask(old_reg_val, mask, new);
  35  *
  36  * The numbers 10 and 5 could for example come from data
  37  * tables which describe all bitfields in all registers.
  38  */
  39
  40 #include <linux/types.h>
  41
  42 /* Produces a mask of set bits covering a range of a uint value */
  43 static inline uint bitfield_mask(uint shift, uint width)
  44 {
  45         return ((1 << width) - 1) << shift;
  46 }
  47
  48 /* Extract the value of a bitfield found within a given register value */
  49 static inline uint bitfield_extract(uint reg_val, uint shift, uint width)
  50 {
  51         return (reg_val & bitfield_mask(shift, width)) >> shift;
  52 }
  53
  54 /*
  55  * Replace the value of a bitfield found within a given register value
  56  * Returns the newly modified uint value with the replaced field.
  57  */
  58 static inline uint bitfield_replace(uint reg_val, uint shift, uint width,
  59                                     uint bitfield_val)
  60 {
  61         uint mask = bitfield_mask(shift, width);
  62
  63         return (reg_val & ~mask) | ((bitfield_val << shift) & mask);
  64 }
  65
  66 /* Produces a shift of the bitfield given a mask */
  67 static inline uint bitfield_shift(uint mask)
  68 {
  69         return mask ? ffs(mask) - 1 : 0;
  70 }
  71
  72 /* Extract the value of a bitfield found within a given register value */
  73 static inline uint bitfield_extract_by_mask(uint reg_val, uint mask)
  74 {
  75         uint shift = bitfield_shift(mask);
  76
  77         return (reg_val & mask) >> shift;
  78 }
  79
  80 /*
  81  * Replace the value of a bitfield found within a given register value
  82  * Returns the newly modified uint value with the replaced field.
  83  */
  84 static inline uint bitfield_replace_by_mask(uint reg_val, uint mask,
  85                                             uint bitfield_val)
  86 {
  87         uint shift = bitfield_shift(mask);
  88
  89         return (reg_val & ~mask) | ((bitfield_val << shift) & mask);
  90 }