// SPDX-License-Identifier: GPL-2.0
/*
* Generic Reed Solomon encoder / decoder library
*
* Copyright (C) 2004 Thomas Gleixner ([email protected])
*
* Reed Solomon code lifted from reed solomon library written by Phil Karn
* Copyright 2002 Phil Karn, KA9Q
*
* Description:
*
* The generic Reed Solomon library provides runtime configurable
* encoding / decoding of RS codes.
*
* Each user must call init_rs to get a pointer to a rs_control structure
* for the given rs parameters. The control struct is unique per instance.
* It points to a codec which can be shared by multiple control structures.
* If a codec is newly allocated then the polynomial arrays for fast
* encoding / decoding are built. This can take some time so make sure not
* to call this function from a time critical path. Usually a module /
* driver should initialize the necessary rs_control structure on module /
* driver init and release it on exit.
*
* The encoding puts the calculated syndrome into a given syndrome buffer.
*
* The decoding is a two step process. The first step calculates the
* syndrome over the received (data + syndrome) and calls the second stage,
* which does the decoding / error correction itself. Many hw encoders
* provide a syndrome calculation over the received data + syndrome and can
* call the second stage directly.
*/
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/rslib.h>
#include <linux/slab.h>
#include <linux/mutex.h>
enum {
RS_DECODE_LAMBDA,
RS_DECODE_SYN,
RS_DECODE_B,
RS_DECODE_T,
RS_DECODE_OMEGA,
RS_DECODE_ROOT,
RS_DECODE_REG,
RS_DECODE_LOC,
RS_DECODE_NUM_BUFFERS
};
/* This list holds all currently allocated rs codec structures */
static LIST_HEAD(codec_list);
/* Protection for the list */
static DEFINE_MUTEX(rslistlock);
/**
* codec_init - Initialize a Reed-Solomon codec
* @symsize: symbol size, bits (1-8)
* @gfpoly: Field generator polynomial coefficients
* @gffunc: Field generator function
* @fcr: first root of RS code generator polynomial, index form
* @prim: primitive element to generate polynomial roots
* @nroots: RS code generator polynomial degree (number of roots)
* @gfp: GFP_ flags for allocations
*
* Allocate a codec structure and the polynom arrays for faster
* en/decoding. Fill the arrays according to the given parameters.
*/
static struct rs_codec *codec_init(int symsize, int gfpoly, int (*gffunc)(int),
int fcr, int prim, int nroots, gfp_t gfp)
{
int i, j, sr, root, iprim;
struct rs_codec *rs;
rs = kzalloc(sizeof(*rs), gfp);
if (!rs)
return NULL;
INIT_LIST_HEAD(&rs->list);
rs->mm = symsize;
rs->nn = (1 << symsize) - 1;
rs->fcr = fcr;
rs->prim = prim;
rs->nroots = nroots;
rs->gfpoly = gfpoly;
rs->gffunc = gffunc;
/* Allocate the arrays */
rs->alpha_to = kmalloc_array(rs->nn + 1, sizeof(uint16_t), gfp);
if (rs->alpha_to == NULL)
goto err;
rs->index_of = kmalloc_array(rs->nn + 1, sizeof(uint16_t), gfp);
if (rs->index_of == NULL)
goto err;
rs->genpoly = kmalloc_array(rs->nroots + 1, sizeof(uint16_t), gfp);
if(rs->genpoly == NULL)
goto err;
/* Generate Galois field lookup tables */
rs->index_of[0] = rs->nn; /* log(zero) = -inf */
rs->alpha_to[rs->nn] = 0; /* alpha**-inf = 0 */
if (gfpoly) {
sr = 1;
for (i = 0; i < rs->nn; i++) {
rs->index_of[sr] = i;
rs->alpha_to[i] = sr;
sr <<= 1;
if (sr & (1 << symsize))
sr ^= gfpoly;
sr &= rs->nn;
}
} else {
sr = gffunc(0);
for (i = 0; i < rs->nn; i++) {
rs->index_of[sr] = i;
rs->alpha_to[i] = sr;
sr = gffunc(sr);
}
}
/* If it's not primitive, exit */
if(sr != rs->alpha_to[0])
goto err;
/* Find prim-th root of 1, used in decoding */
for(iprim = 1; (iprim % prim) != 0; iprim += rs->nn);
/* prim-th root of 1, index form */
rs->iprim = iprim / prim;
/* Form RS code generator polynomial from its roots */
rs->genpoly[0] = 1;
for (i = 0, root = fcr * prim; i < nroots; i++, root += prim) {
rs->genpoly[i + 1] = 1;
/* Multiply rs->genpoly[] by @**(root + x) */
for (j = i; j > 0; j--) {
if (rs->genpoly[j] != 0) {
rs->genpoly[j] = rs->genpoly[j -1] ^
rs->alpha_to[rs_modnn(rs,
rs->index_of[rs->genpoly[j]] + root)];
} else
rs->genpoly[j] = rs->genpoly[j - 1];
}
/* rs->genpoly[0] can never be zero */
rs->genpoly[0] =
rs->alpha_to[rs_modnn(rs,
rs->index_of[rs->genpoly[0]] + root)];
}
/* convert rs->genpoly[] to index form for quicker encoding */
for (i = 0; i <= nroots; i++)
rs->genpoly[i] = rs->index_of[rs->genpoly[i]];
rs->users = 1;
list_add(&rs->list, &codec_list);
return rs;
err:
kfree(rs->genpoly);
kfree(rs->index_of);
kfree(rs->alpha_to);
kfree(rs);
return NULL;
}
/**
* free_rs - Free the rs control structure
* @rs: The control structure which is not longer used by the
* caller
*
* Free the control structure. If @rs is the last user of the associated
* codec, free the codec as well.
*/
void free_rs(struct rs_control *rs)
{
struct rs_codec *cd;
if (!rs)
return;
cd = rs->codec;
mutex_lock(&rslistlock);
cd->users--;
if(!cd->users) {
list_del(&cd->list);
kfree(cd->alpha_to);
kfree(cd->index_of);
kfree(cd->genpoly);
kfree(cd);
}
mutex_unlock(&rslistlock);
kfree(rs);
}
EXPORT_SYMBOL_GPL(free_rs);
/**
* init_rs_internal - Allocate rs control, find a matching codec or allocate a new one
* @symsize: the symbol size (number of bits)
* @gfpoly: the extended Galois field generator polynomial coefficients,
* with the 0th coefficient in the low order bit. The polynomial
* must be primitive;
* @gffunc: pointer to function to generate the next field element,
* or the multiplicative identity element if given 0. Used
* instead of gfpoly if gfpoly is 0
* @fcr: the first consecutive root of the rs code generator polynomial
* in index form
* @prim: primitive element to generate polynomial roots
* @nroots: RS code generator polynomial degree (number of roots)
* @gfp: GFP_ flags for allocations
*/
static struct rs_control *init_rs_internal(int symsize, int gfpoly,
int (*gffunc)(int), int fcr,
int prim, int nroots, gfp_t gfp)
{
struct list_head *tmp;
struct rs_control *rs;
unsigned int bsize;
/* Sanity checks */
if (symsize < 1)
return NULL;
if (fcr < 0 || fcr >= (1<<symsize))
return NULL;
if (prim <= 0 || prim >= (1<<symsize))
return NULL;
if (nroots < 0 || nroots >= (1<<symsize))
return NULL;
/*
* The decoder needs buffers in each control struct instance to
* avoid variable size or large fixed size allocations on
* stack. Size the buffers to arrays of [nroots + 1].
*/
bsize = sizeof(uint16_t) * RS_DECODE_NUM_BUFFERS * (nroots + 1);
rs = kzalloc(sizeof(*rs) + bsize, gfp);
if (!rs)
return NULL;
mutex_lock(&rslistlock);
/* Walk through the list and look for a matching entry */
list_for_each(tmp, &codec_list) {
struct rs_codec *cd = list_entry(tmp, struct rs_codec, list);
if (symsize != cd->mm)
continue;
if (gfpoly != cd->gfpoly)
continue;
if (gffunc != cd->gffunc)
continue;
if (fcr != cd->fcr)
continue;
if (prim != cd->prim)
continue;
if (nroots != cd->nroots)
continue;
/* We have a matching one already */
cd->users++;
rs->codec = cd;
goto out;
}
/* Create a new one */
rs->codec = codec_init(symsize, gfpoly, gffunc, fcr, prim, nroots, gfp);
if (!rs->codec) {
kfree(rs);
rs = NULL;
}
out:
mutex_unlock(&rslistlock);
return rs;
}
/**
* init_rs_gfp - Create a RS control struct and initialize it
* @symsize: the symbol size (number of bits)
* @gfpoly: the extended Galois field generator polynomial coefficients,
* with the 0th coefficient in the low order bit. The polynomial
* must be primitive;
* @fcr: the first consecutive root of the rs code generator polynomial
* in index form
* @prim: primitive element to generate polynomial roots
* @nroots: RS code generator polynomial degree (number of roots)
* @gfp: Memory allocation flags.
*/
struct rs_control *init_rs_gfp(int symsize, int gfpoly, int fcr, int prim,
int nroots, gfp_t gfp)
{
return init_rs_internal(symsize, gfpoly, NULL, fcr, prim, nroots, gfp);
}
EXPORT_SYMBOL_GPL(init_rs_gfp);
/**
* init_rs_non_canonical - Allocate rs control struct for fields with
* non-canonical representation
* @symsize: the symbol size (number of bits)
* @gffunc: pointer to function to generate the next field element,
* or the multiplicative identity element if given 0. Used
* instead of gfpoly if gfpoly is 0
* @fcr: the first consecutive root of the rs code generator polynomial
* in index form
* @prim: primitive element to generate polynomial roots
* @nroots: RS code generator polynomial degree (number of roots)
*/
struct rs_control *init_rs_non_canonical(int symsize, int (*gffunc)(int),
int fcr, int prim, int nroots)
{
return init_rs_internal(symsize, 0, gffunc, fcr, prim, nroots,
GFP_KERNEL);
}
EXPORT_SYMBOL_GPL(init_rs_non_canonical);
#ifdef CONFIG_REED_SOLOMON_ENC8
/**
* encode_rs8 - Calculate the parity for data values (8bit data width)
* @rsc: the rs control structure
* @data: data field of a given type
* @len: data length
* @par: parity data, must be initialized by caller (usually all 0)
* @invmsk: invert data mask (will be xored on data)
*
* The parity uses a uint16_t data type to enable
* symbol size > 8. The calling code must take care of encoding of the
* syndrome result for storage itself.
*/
int encode_rs8(struct rs_control *rsc, uint8_t *data, int len, uint16_t *par,
uint16_t invmsk)
{
#include "encode_rs.c"
}
EXPORT_SYMBOL_GPL(encode_rs8);
#endif
#ifdef CONFIG_REED_SOLOMON_DEC8
/**
* decode_rs8 - Decode codeword (8bit data width)
* @rsc: the rs control structure
* @data: data field of a given type
* @par: received parity data field
* @len: data length
* @s: syndrome data field, must be in index form
* (if NULL, syndrome is calculated)
* @no_eras: number of erasures
* @eras_pos: position of erasures, can be NULL
* @invmsk: invert data mask (will be xored on data, not on parity!)
* @corr: buffer to store correction bitmask on eras_pos
*
* The syndrome and parity uses a uint16_t data type to enable
* symbol size > 8. The calling code must take care of decoding of the
* syndrome result and the received parity before calling this code.
*
* Note: The rs_control struct @rsc contains buffers which are used for
* decoding, so the caller has to ensure that decoder invocations are
* serialized.
*
* Returns the number of corrected symbols or -EBADMSG for uncorrectable
* errors. The count includes errors in the parity.
*/
int decode_rs8(struct rs_control *rsc, uint8_t *data, uint16_t *par, int len,
uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
uint16_t *corr)
{
#include "decode_rs.c"
}
EXPORT_SYMBOL_GPL(decode_rs8);
#endif
#ifdef CONFIG_REED_SOLOMON_ENC16
/**
* encode_rs16 - Calculate the parity for data values (16bit data width)
* @rsc: the rs control structure
* @data: data field of a given type
* @len: data length
* @par: parity data, must be initialized by caller (usually all 0)
* @invmsk: invert data mask (will be xored on data, not on parity!)
*
* Each field in the data array contains up to symbol size bits of valid data.
*/
int encode_rs16(struct rs_control *rsc, uint16_t *data, int len, uint16_t *par,
uint16_t invmsk)
{
#include "encode_rs.c"
}
EXPORT_SYMBOL_GPL(encode_rs16);
#endif
#ifdef CONFIG_REED_SOLOMON_DEC16
/**
* decode_rs16 - Decode codeword (16bit data width)
* @rsc: the rs control structure
* @data: data field of a given type
* @par: received parity data field
* @len: data length
* @s: syndrome data field, must be in index form
* (if NULL, syndrome is calculated)
* @no_eras: number of erasures
* @eras_pos: position of erasures, can be NULL
* @invmsk: invert data mask (will be xored on data, not on parity!)
* @corr: buffer to store correction bitmask on eras_pos
*
* Each field in the data array contains up to symbol size bits of valid data.
*
* Note: The rc_control struct @rsc contains buffers which are used for
* decoding, so the caller has to ensure that decoder invocations are
* serialized.
*
* Returns the number of corrected symbols or -EBADMSG for uncorrectable
* errors. The count includes errors in the parity.
*/
int decode_rs16(struct rs_control *rsc, uint16_t *data, uint16_t *par, int len,
uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
uint16_t *corr)
{
#include "decode_rs.c"
}
EXPORT_SYMBOL_GPL(decode_rs16);
#endif
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Reed Solomon encoder/decoder");
MODULE_AUTHOR("Phil Karn, Thomas Gleixner");
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