Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
[platform/kernel/linux-starfive.git] / lib / packing.c
1 // SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
2 /* Copyright 2016-2018 NXP
3  * Copyright (c) 2018-2019, Vladimir Oltean <olteanv@gmail.com>
4  */
5 #include <linux/packing.h>
6 #include <linux/module.h>
7 #include <linux/bitops.h>
8 #include <linux/errno.h>
9 #include <linux/types.h>
10 #include <linux/bitrev.h>
11
12 static int get_le_offset(int offset)
13 {
14         int closest_multiple_of_4;
15
16         closest_multiple_of_4 = (offset / 4) * 4;
17         offset -= closest_multiple_of_4;
18         return closest_multiple_of_4 + (3 - offset);
19 }
20
21 static int get_reverse_lsw32_offset(int offset, size_t len)
22 {
23         int closest_multiple_of_4;
24         int word_index;
25
26         word_index = offset / 4;
27         closest_multiple_of_4 = word_index * 4;
28         offset -= closest_multiple_of_4;
29         word_index = (len / 4) - word_index - 1;
30         return word_index * 4 + offset;
31 }
32
33 static void adjust_for_msb_right_quirk(u64 *to_write, int *box_start_bit,
34                                        int *box_end_bit, u8 *box_mask)
35 {
36         int box_bit_width = *box_start_bit - *box_end_bit + 1;
37         int new_box_start_bit, new_box_end_bit;
38
39         *to_write >>= *box_end_bit;
40         *to_write = bitrev8(*to_write) >> (8 - box_bit_width);
41         *to_write <<= *box_end_bit;
42
43         new_box_end_bit   = box_bit_width - *box_start_bit - 1;
44         new_box_start_bit = box_bit_width - *box_end_bit - 1;
45         *box_mask = GENMASK_ULL(new_box_start_bit, new_box_end_bit);
46         *box_start_bit = new_box_start_bit;
47         *box_end_bit   = new_box_end_bit;
48 }
49
50 /**
51  * packing - Convert numbers (currently u64) between a packed and an unpacked
52  *           format. Unpacked means laid out in memory in the CPU's native
53  *           understanding of integers, while packed means anything else that
54  *           requires translation.
55  *
56  * @pbuf: Pointer to a buffer holding the packed value.
57  * @uval: Pointer to an u64 holding the unpacked value.
58  * @startbit: The index (in logical notation, compensated for quirks) where
59  *            the packed value starts within pbuf. Must be larger than, or
60  *            equal to, endbit.
61  * @endbit: The index (in logical notation, compensated for quirks) where
62  *          the packed value ends within pbuf. Must be smaller than, or equal
63  *          to, startbit.
64  * @pbuflen: The length in bytes of the packed buffer pointed to by @pbuf.
65  * @op: If PACK, then uval will be treated as const pointer and copied (packed)
66  *      into pbuf, between startbit and endbit.
67  *      If UNPACK, then pbuf will be treated as const pointer and the logical
68  *      value between startbit and endbit will be copied (unpacked) to uval.
69  * @quirks: A bit mask of QUIRK_LITTLE_ENDIAN, QUIRK_LSW32_IS_FIRST and
70  *          QUIRK_MSB_ON_THE_RIGHT.
71  *
72  * Return: 0 on success, EINVAL or ERANGE if called incorrectly. Assuming
73  *         correct usage, return code may be discarded.
74  *         If op is PACK, pbuf is modified.
75  *         If op is UNPACK, uval is modified.
76  */
77 int packing(void *pbuf, u64 *uval, int startbit, int endbit, size_t pbuflen,
78             enum packing_op op, u8 quirks)
79 {
80         /* Number of bits for storing "uval"
81          * also width of the field to access in the pbuf
82          */
83         u64 value_width;
84         /* Logical byte indices corresponding to the
85          * start and end of the field.
86          */
87         int plogical_first_u8, plogical_last_u8, box;
88
89         /* startbit is expected to be larger than endbit */
90         if (startbit < endbit)
91                 /* Invalid function call */
92                 return -EINVAL;
93
94         value_width = startbit - endbit + 1;
95         if (value_width > 64)
96                 return -ERANGE;
97
98         /* Check if "uval" fits in "value_width" bits.
99          * If value_width is 64, the check will fail, but any
100          * 64-bit uval will surely fit.
101          */
102         if (op == PACK && value_width < 64 && (*uval >= (1ull << value_width)))
103                 /* Cannot store "uval" inside "value_width" bits.
104                  * Truncating "uval" is most certainly not desirable,
105                  * so simply erroring out is appropriate.
106                  */
107                 return -ERANGE;
108
109         /* Initialize parameter */
110         if (op == UNPACK)
111                 *uval = 0;
112
113         /* Iterate through an idealistic view of the pbuf as an u64 with
114          * no quirks, u8 by u8 (aligned at u8 boundaries), from high to low
115          * logical bit significance. "box" denotes the current logical u8.
116          */
117         plogical_first_u8 = startbit / 8;
118         plogical_last_u8  = endbit / 8;
119
120         for (box = plogical_first_u8; box >= plogical_last_u8; box--) {
121                 /* Bit indices into the currently accessed 8-bit box */
122                 int box_start_bit, box_end_bit, box_addr;
123                 u8  box_mask;
124                 /* Corresponding bits from the unpacked u64 parameter */
125                 int proj_start_bit, proj_end_bit;
126                 u64 proj_mask;
127
128                 /* This u8 may need to be accessed in its entirety
129                  * (from bit 7 to bit 0), or not, depending on the
130                  * input arguments startbit and endbit.
131                  */
132                 if (box == plogical_first_u8)
133                         box_start_bit = startbit % 8;
134                 else
135                         box_start_bit = 7;
136                 if (box == plogical_last_u8)
137                         box_end_bit = endbit % 8;
138                 else
139                         box_end_bit = 0;
140
141                 /* We have determined the box bit start and end.
142                  * Now we calculate where this (masked) u8 box would fit
143                  * in the unpacked (CPU-readable) u64 - the u8 box's
144                  * projection onto the unpacked u64. Though the
145                  * box is u8, the projection is u64 because it may fall
146                  * anywhere within the unpacked u64.
147                  */
148                 proj_start_bit = ((box * 8) + box_start_bit) - endbit;
149                 proj_end_bit   = ((box * 8) + box_end_bit) - endbit;
150                 proj_mask = GENMASK_ULL(proj_start_bit, proj_end_bit);
151                 box_mask  = GENMASK_ULL(box_start_bit, box_end_bit);
152
153                 /* Determine the offset of the u8 box inside the pbuf,
154                  * adjusted for quirks. The adjusted box_addr will be used for
155                  * effective addressing inside the pbuf (so it's not
156                  * logical any longer).
157                  */
158                 box_addr = pbuflen - box - 1;
159                 if (quirks & QUIRK_LITTLE_ENDIAN)
160                         box_addr = get_le_offset(box_addr);
161                 if (quirks & QUIRK_LSW32_IS_FIRST)
162                         box_addr = get_reverse_lsw32_offset(box_addr,
163                                                             pbuflen);
164
165                 if (op == UNPACK) {
166                         u64 pval;
167
168                         /* Read from pbuf, write to uval */
169                         pval = ((u8 *)pbuf)[box_addr] & box_mask;
170                         if (quirks & QUIRK_MSB_ON_THE_RIGHT)
171                                 adjust_for_msb_right_quirk(&pval,
172                                                            &box_start_bit,
173                                                            &box_end_bit,
174                                                            &box_mask);
175
176                         pval >>= box_end_bit;
177                         pval <<= proj_end_bit;
178                         *uval &= ~proj_mask;
179                         *uval |= pval;
180                 } else {
181                         u64 pval;
182
183                         /* Write to pbuf, read from uval */
184                         pval = (*uval) & proj_mask;
185                         pval >>= proj_end_bit;
186                         if (quirks & QUIRK_MSB_ON_THE_RIGHT)
187                                 adjust_for_msb_right_quirk(&pval,
188                                                            &box_start_bit,
189                                                            &box_end_bit,
190                                                            &box_mask);
191
192                         pval <<= box_end_bit;
193                         ((u8 *)pbuf)[box_addr] &= ~box_mask;
194                         ((u8 *)pbuf)[box_addr] |= pval;
195                 }
196         }
197         return 0;
198 }
199 EXPORT_SYMBOL(packing);
200
201 MODULE_DESCRIPTION("Generic bitfield packing and unpacking");