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