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- // SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
- /* Copyright 2016-2018 NXP
- * Copyright (c) 2018-2019, Vladimir Oltean <[email protected]>
- */
- #include <linux/packing.h>
- #include <linux/module.h>
- #include <linux/bitops.h>
- #include <linux/errno.h>
- #include <linux/types.h>
- static int get_le_offset(int offset)
- {
- int closest_multiple_of_4;
- closest_multiple_of_4 = (offset / 4) * 4;
- offset -= closest_multiple_of_4;
- return closest_multiple_of_4 + (3 - offset);
- }
- static int get_reverse_lsw32_offset(int offset, size_t len)
- {
- int closest_multiple_of_4;
- int word_index;
- word_index = offset / 4;
- closest_multiple_of_4 = word_index * 4;
- offset -= closest_multiple_of_4;
- word_index = (len / 4) - word_index - 1;
- return word_index * 4 + offset;
- }
- static u64 bit_reverse(u64 val, unsigned int width)
- {
- u64 new_val = 0;
- unsigned int bit;
- unsigned int i;
- for (i = 0; i < width; i++) {
- bit = (val & (1 << i)) != 0;
- new_val |= (bit << (width - i - 1));
- }
- return new_val;
- }
- static void adjust_for_msb_right_quirk(u64 *to_write, int *box_start_bit,
- int *box_end_bit, u8 *box_mask)
- {
- int box_bit_width = *box_start_bit - *box_end_bit + 1;
- int new_box_start_bit, new_box_end_bit;
- *to_write >>= *box_end_bit;
- *to_write = bit_reverse(*to_write, box_bit_width);
- *to_write <<= *box_end_bit;
- new_box_end_bit = box_bit_width - *box_start_bit - 1;
- new_box_start_bit = box_bit_width - *box_end_bit - 1;
- *box_mask = GENMASK_ULL(new_box_start_bit, new_box_end_bit);
- *box_start_bit = new_box_start_bit;
- *box_end_bit = new_box_end_bit;
- }
- /**
- * packing - Convert numbers (currently u64) between a packed and an unpacked
- * format. Unpacked means laid out in memory in the CPU's native
- * understanding of integers, while packed means anything else that
- * requires translation.
- *
- * @pbuf: Pointer to a buffer holding the packed value.
- * @uval: Pointer to an u64 holding the unpacked value.
- * @startbit: The index (in logical notation, compensated for quirks) where
- * the packed value starts within pbuf. Must be larger than, or
- * equal to, endbit.
- * @endbit: The index (in logical notation, compensated for quirks) where
- * the packed value ends within pbuf. Must be smaller than, or equal
- * to, startbit.
- * @pbuflen: The length in bytes of the packed buffer pointed to by @pbuf.
- * @op: If PACK, then uval will be treated as const pointer and copied (packed)
- * into pbuf, between startbit and endbit.
- * If UNPACK, then pbuf will be treated as const pointer and the logical
- * value between startbit and endbit will be copied (unpacked) to uval.
- * @quirks: A bit mask of QUIRK_LITTLE_ENDIAN, QUIRK_LSW32_IS_FIRST and
- * QUIRK_MSB_ON_THE_RIGHT.
- *
- * Return: 0 on success, EINVAL or ERANGE if called incorrectly. Assuming
- * correct usage, return code may be discarded.
- * If op is PACK, pbuf is modified.
- * If op is UNPACK, uval is modified.
- */
- int packing(void *pbuf, u64 *uval, int startbit, int endbit, size_t pbuflen,
- enum packing_op op, u8 quirks)
- {
- /* Number of bits for storing "uval"
- * also width of the field to access in the pbuf
- */
- u64 value_width;
- /* Logical byte indices corresponding to the
- * start and end of the field.
- */
- int plogical_first_u8, plogical_last_u8, box;
- /* startbit is expected to be larger than endbit */
- if (startbit < endbit)
- /* Invalid function call */
- return -EINVAL;
- value_width = startbit - endbit + 1;
- if (value_width > 64)
- return -ERANGE;
- /* Check if "uval" fits in "value_width" bits.
- * If value_width is 64, the check will fail, but any
- * 64-bit uval will surely fit.
- */
- if (op == PACK && value_width < 64 && (*uval >= (1ull << value_width)))
- /* Cannot store "uval" inside "value_width" bits.
- * Truncating "uval" is most certainly not desirable,
- * so simply erroring out is appropriate.
- */
- return -ERANGE;
- /* Initialize parameter */
- if (op == UNPACK)
- *uval = 0;
- /* Iterate through an idealistic view of the pbuf as an u64 with
- * no quirks, u8 by u8 (aligned at u8 boundaries), from high to low
- * logical bit significance. "box" denotes the current logical u8.
- */
- plogical_first_u8 = startbit / 8;
- plogical_last_u8 = endbit / 8;
- for (box = plogical_first_u8; box >= plogical_last_u8; box--) {
- /* Bit indices into the currently accessed 8-bit box */
- int box_start_bit, box_end_bit, box_addr;
- u8 box_mask;
- /* Corresponding bits from the unpacked u64 parameter */
- int proj_start_bit, proj_end_bit;
- u64 proj_mask;
- /* This u8 may need to be accessed in its entirety
- * (from bit 7 to bit 0), or not, depending on the
- * input arguments startbit and endbit.
- */
- if (box == plogical_first_u8)
- box_start_bit = startbit % 8;
- else
- box_start_bit = 7;
- if (box == plogical_last_u8)
- box_end_bit = endbit % 8;
- else
- box_end_bit = 0;
- /* We have determined the box bit start and end.
- * Now we calculate where this (masked) u8 box would fit
- * in the unpacked (CPU-readable) u64 - the u8 box's
- * projection onto the unpacked u64. Though the
- * box is u8, the projection is u64 because it may fall
- * anywhere within the unpacked u64.
- */
- proj_start_bit = ((box * 8) + box_start_bit) - endbit;
- proj_end_bit = ((box * 8) + box_end_bit) - endbit;
- proj_mask = GENMASK_ULL(proj_start_bit, proj_end_bit);
- box_mask = GENMASK_ULL(box_start_bit, box_end_bit);
- /* Determine the offset of the u8 box inside the pbuf,
- * adjusted for quirks. The adjusted box_addr will be used for
- * effective addressing inside the pbuf (so it's not
- * logical any longer).
- */
- box_addr = pbuflen - box - 1;
- if (quirks & QUIRK_LITTLE_ENDIAN)
- box_addr = get_le_offset(box_addr);
- if (quirks & QUIRK_LSW32_IS_FIRST)
- box_addr = get_reverse_lsw32_offset(box_addr,
- pbuflen);
- if (op == UNPACK) {
- u64 pval;
- /* Read from pbuf, write to uval */
- pval = ((u8 *)pbuf)[box_addr] & box_mask;
- if (quirks & QUIRK_MSB_ON_THE_RIGHT)
- adjust_for_msb_right_quirk(&pval,
- &box_start_bit,
- &box_end_bit,
- &box_mask);
- pval >>= box_end_bit;
- pval <<= proj_end_bit;
- *uval &= ~proj_mask;
- *uval |= pval;
- } else {
- u64 pval;
- /* Write to pbuf, read from uval */
- pval = (*uval) & proj_mask;
- pval >>= proj_end_bit;
- if (quirks & QUIRK_MSB_ON_THE_RIGHT)
- adjust_for_msb_right_quirk(&pval,
- &box_start_bit,
- &box_end_bit,
- &box_mask);
- pval <<= box_end_bit;
- ((u8 *)pbuf)[box_addr] &= ~box_mask;
- ((u8 *)pbuf)[box_addr] |= pval;
- }
- }
- return 0;
- }
- EXPORT_SYMBOL(packing);
- MODULE_LICENSE("GPL v2");
- MODULE_DESCRIPTION("Generic bitfield packing and unpacking");
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