[U-Boot] [PATCH 1/2] nand: Merge BCH code from Linux nand driver

Hitz, Christian christian.hitz at aizo.com
Wed Oct 5 10:45:31 CEST 2011


This patch merges the BCH ECC algorithm from the 3.0 Linux kernel.
This enables U-Boot to support modern NAND flash chips that
require more than 1-bit of ECC in software.

Signed-off-by: Christian Hitz <christian.hitz at aizo.com>
---
 drivers/mtd/nand/Makefile    |    1 +
 drivers/mtd/nand/nand_base.c |   39 ++-
 drivers/mtd/nand/nand_bch.c  |  236 ++++++++
 drivers/mtd/nand/nand_ids.c  |   35 ++
 include/linux/bch.h          |   79 +++
 include/linux/mtd/nand.h     |   10 +-
 include/linux/mtd/nand_bch.h |   72 +++
 lib/Makefile                 |    1 +
 lib/bch.c                    | 1358 ++++++++++++++++++++++++++++++++++++++++++
 9 files changed, 1823 insertions(+), 8 deletions(-)
 create mode 100644 drivers/mtd/nand/nand_bch.c
 create mode 100644 include/linux/bch.h
 create mode 100644 include/linux/mtd/nand_bch.h
 create mode 100644 lib/bch.c

diff --git a/drivers/mtd/nand/Makefile b/drivers/mtd/nand/Makefile
index dae2442..3781cc1 100644
--- a/drivers/mtd/nand/Makefile
+++ b/drivers/mtd/nand/Makefile
@@ -38,6 +38,7 @@ COBJS-y += nand_util.o
 endif
 COBJS-y += nand_ecc.o
 COBJS-y += nand_base.o
+COBJS-$(CONFIG_NAND_ECC_BCH) += nand_bch.o

 COBJS-$(CONFIG_NAND_ATMEL) += atmel_nand.o
 COBJS-$(CONFIG_DRIVER_NAND_BFIN) += bfin_nand.o
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 6aac6a2..8212319 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -43,6 +43,7 @@
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/nand.h>
 #include <linux/mtd/nand_ecc.h>
+#include <linux/mtd/nand_bch.h>

 #ifdef CONFIG_MTD_PARTITIONS
 #include <linux/mtd/partitions.h>
@@ -2763,7 +2764,7 @@ int nand_scan_tail(struct mtd_info *mtd)
        /*
         * If no default placement scheme is given, select an appropriate one
         */
-       if (!chip->ecc.layout) {
+       if (!chip->ecc.layout && (chip->ecc.mode != NAND_ECC_SOFT_BCH)) {
                switch (mtd->oobsize) {
                case 8:
                        chip->ecc.layout = &nand_oob_8;
@@ -2864,6 +2865,39 @@ int nand_scan_tail(struct mtd_info *mtd)
                chip->ecc.bytes = 3;
                break;

+       case NAND_ECC_SOFT_BCH:
+               if (!mtd_nand_has_bch()) {
+                       printk(KERN_WARNING "CONFIG_MTD_ECC_BCH not enabled\n");
+                       BUG();
+               }
+               chip->ecc.calculate = nand_bch_calculate_ecc;
+               chip->ecc.correct = nand_bch_correct_data;
+               chip->ecc.read_page = nand_read_page_swecc;
+               chip->ecc.read_subpage = nand_read_subpage;
+               chip->ecc.write_page = nand_write_page_swecc;
+               chip->ecc.read_page_raw = nand_read_page_raw;
+               chip->ecc.write_page_raw = nand_write_page_raw;
+               chip->ecc.read_oob = nand_read_oob_std;
+               chip->ecc.write_oob = nand_write_oob_std;
+               /*
+                * Board driver should supply ecc.size and ecc.bytes values to
+                * select how many bits are correctable; see nand_bch_init()
+                * for details.
+                * Otherwise, default to 4 bits for large page devices
+                */
+               if (!chip->ecc.size && (mtd->oobsize >= 64)) {
+                       chip->ecc.size = 512;
+                       chip->ecc.bytes = 7;
+               }
+               chip->ecc.priv = nand_bch_init(mtd,
+                                              chip->ecc.size,
+                                              chip->ecc.bytes,
+                                              &chip->ecc.layout);
+               if (!chip->ecc.priv) {
+                       printk(KERN_WARNING "BCH ECC initialization failed!\n");
+               }
+               break;
+
        case NAND_ECC_NONE:
                printk(KERN_WARNING "NAND_ECC_NONE selected by board driver. "
                       "This is not recommended !!\n");
@@ -2989,6 +3023,9 @@ void nand_release(struct mtd_info *mtd)
 {
        struct nand_chip *chip = mtd->priv;

+       if (chip->ecc.mode == NAND_ECC_SOFT_BCH)
+               nand_bch_free((struct nand_bch_control *)chip->ecc.priv);
+
 #ifdef CONFIG_MTD_PARTITIONS
        /* Deregister partitions */
        del_mtd_partitions(mtd);
diff --git a/drivers/mtd/nand/nand_bch.c b/drivers/mtd/nand/nand_bch.c
new file mode 100644
index 0000000..7835fce
--- /dev/null
+++ b/drivers/mtd/nand/nand_bch.c
@@ -0,0 +1,236 @@
+/*
+ * This file provides ECC correction for more than 1 bit per block of data,
+ * using binary BCH codes. It relies on the generic BCH library lib/bch.c.
+ *
+ * Copyright (c) 2011 Ivan Djelic <ivan.djelic at parrot.com>
+ *
+ * This file is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 or (at your option) any
+ * later version.
+ *
+ * This file is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this file; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#include <common.h>
+/*#include <asm/io.h>*/
+#include <linux/types.h>
+
+#include <linux/bitops.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/nand.h>
+#include <linux/mtd/nand_bch.h>
+#include <linux/bch.h>
+#include <malloc.h>
+
+/**
+ * struct nand_bch_control - private NAND BCH control structure
+ * @bch:       BCH control structure
+ * @ecclayout: private ecc layout for this BCH configuration
+ * @errloc:    error location array
+ * @eccmask:   XOR ecc mask, allows erased pages to be decoded as valid
+ */
+struct nand_bch_control {
+       struct bch_control   *bch;
+       struct nand_ecclayout ecclayout;
+       unsigned int         *errloc;
+       unsigned char        *eccmask;
+};
+
+/**
+ * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
+ * @mtd:       MTD block structure
+ * @buf:       input buffer with raw data
+ * @code:      output buffer with ECC
+ */
+int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
+                          unsigned char *code)
+{
+       const struct nand_chip *chip = mtd->priv;
+       struct nand_bch_control *nbc = chip->ecc.priv;
+       unsigned int i;
+
+       memset(code, 0, chip->ecc.bytes);
+       encode_bch(nbc->bch, buf, chip->ecc.size, code);
+
+       /* apply mask so that an erased page is a valid codeword */
+       for (i = 0; i < chip->ecc.bytes; i++)
+               code[i] ^= nbc->eccmask[i];
+
+       return 0;
+}
+
+/**
+ * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
+ * @mtd:       MTD block structure
+ * @buf:       raw data read from the chip
+ * @read_ecc:  ECC from the chip
+ * @calc_ecc:  the ECC calculated from raw data
+ *
+ * Detect and correct bit errors for a data byte block
+ */
+int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
+                         unsigned char *read_ecc, unsigned char *calc_ecc)
+{
+       const struct nand_chip *chip = mtd->priv;
+       struct nand_bch_control *nbc = chip->ecc.priv;
+       unsigned int *errloc = nbc->errloc;
+       int i, count;
+
+       count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
+                          NULL, errloc);
+       if (count > 0) {
+               for (i = 0; i < count; i++) {
+                       if (errloc[i] < (chip->ecc.size*8))
+                               /* error is located in data, correct it */
+                               buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
+                       /* else error in ecc, no action needed */
+
+                       MTDDEBUG(MTD_DEBUG_LEVEL0, "%s: corrected bitflip %u\n",
+                             __func__, errloc[i]);
+               }
+       } else if (count < 0) {
+               printk(KERN_ERR "ecc unrecoverable error\n");
+               count = -1;
+       }
+       return count;
+}
+
+/**
+ * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
+ * @mtd:       MTD block structure
+ * @eccsize:   ecc block size in bytes
+ * @eccbytes:  ecc length in bytes
+ * @ecclayout: output default layout
+ *
+ * Returns:
+ *  a pointer to a new NAND BCH control structure, or NULL upon failure
+ *
+ * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
+ * are used to compute BCH parameters m (Galois field order) and t (error
+ * correction capability). @eccbytes should be equal to the number of bytes
+ * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
+ *
+ * Example: to configure 4 bit correction per 512 bytes, you should pass
+ * @eccsize = 512  (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
+ * @eccbytes = 7   (7 bytes are required to store m*t = 13*4 = 52 bits)
+ */
+struct nand_bch_control *
+nand_bch_init(struct mtd_info *mtd, unsigned int eccsize, unsigned int eccbytes,
+             struct nand_ecclayout **ecclayout)
+{
+       unsigned int m, t, eccsteps, i;
+       struct nand_ecclayout *layout;
+       struct nand_bch_control *nbc = NULL;
+       unsigned char *erased_page;
+
+       if (!eccsize || !eccbytes) {
+               printk(KERN_WARNING "ecc parameters not supplied\n");
+               goto fail;
+       }
+
+       m = fls(1+8*eccsize);
+       t = (eccbytes*8)/m;
+
+       nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
+       if (!nbc)
+               goto fail;
+
+       nbc->bch = init_bch(m, t, 0);
+       if (!nbc->bch)
+               goto fail;
+
+       /* verify that eccbytes has the expected value */
+       if (nbc->bch->ecc_bytes != eccbytes) {
+               printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
+                      eccbytes, nbc->bch->ecc_bytes);
+               goto fail;
+       }
+
+       eccsteps = mtd->writesize/eccsize;
+
+       /* if no ecc placement scheme was provided, build one */
+       if (!*ecclayout) {
+
+               /* handle large page devices only */
+               if (mtd->oobsize < 64) {
+                       printk(KERN_WARNING "must provide an oob scheme for "
+                              "oobsize %d\n", mtd->oobsize);
+                       goto fail;
+               }
+
+               layout = &nbc->ecclayout;
+               layout->eccbytes = eccsteps*eccbytes;
+
+               /* reserve 2 bytes for bad block marker */
+               if (layout->eccbytes+2 > mtd->oobsize) {
+                       printk(KERN_WARNING "no suitable oob scheme available "
+                              "for oobsize %d eccbytes %u\n", mtd->oobsize,
+                              eccbytes);
+                       goto fail;
+               }
+               /* put ecc bytes at oob tail */
+               for (i = 0; i < layout->eccbytes; i++)
+                       layout->eccpos[i] = mtd->oobsize-layout->eccbytes+i;
+
+               layout->oobfree[0].offset = 2;
+               layout->oobfree[0].length = mtd->oobsize-2-layout->eccbytes;
+
+               *ecclayout = layout;
+       }
+
+       /* sanity checks */
+       if (8*(eccsize+eccbytes) >= (1 << m)) {
+               printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
+               goto fail;
+       }
+       if ((*ecclayout)->eccbytes != (eccsteps*eccbytes)) {
+               printk(KERN_WARNING "invalid ecc layout\n");
+               goto fail;
+       }
+
+       nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
+       nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
+       if (!nbc->eccmask || !nbc->errloc)
+               goto fail;
+       /*
+        * compute and store the inverted ecc of an erased ecc block
+        */
+       erased_page = kmalloc(eccsize, GFP_KERNEL);
+       if (!erased_page)
+               goto fail;
+
+       memset(erased_page, 0xff, eccsize);
+       memset(nbc->eccmask, 0, eccbytes);
+       encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
+       kfree(erased_page);
+
+       for (i = 0; i < eccbytes; i++)
+               nbc->eccmask[i] ^= 0xff;
+
+       return nbc;
+fail:
+       nand_bch_free(nbc);
+       return NULL;
+}
+
+/**
+ * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
+ * @nbc:       NAND BCH control structure
+ */
+void nand_bch_free(struct nand_bch_control *nbc)
+{
+       if (nbc) {
+               free_bch(nbc->bch);
+               kfree(nbc->errloc);
+               kfree(nbc->eccmask);
+               kfree(nbc);
+       }
+}
diff --git a/drivers/mtd/nand/nand_ids.c b/drivers/mtd/nand/nand_ids.c
index 8d7ea76..3953549 100644
--- a/drivers/mtd/nand/nand_ids.c
+++ b/drivers/mtd/nand/nand_ids.c
@@ -76,9 +76,13 @@ const struct nand_flash_dev nand_flash_ids[] = {

        /*512 Megabit */
        {"NAND 64MiB 1,8V 8-bit",       0xA2, 0,  64, 0, LP_OPTIONS},
+       {"NAND 64MiB 1,8V 8-bit",       0xA0, 0,  64, 0, LP_OPTIONS},
        {"NAND 64MiB 3,3V 8-bit",       0xF2, 0,  64, 0, LP_OPTIONS},
+       {"NAND 64MiB 3,3V 8-bit",       0xD0, 0,  64, 0, LP_OPTIONS},
        {"NAND 64MiB 1,8V 16-bit",      0xB2, 0,  64, 0, LP_OPTIONS16},
+       {"NAND 64MiB 1,8V 16-bit",      0xB0, 0,  64, 0, LP_OPTIONS16},
        {"NAND 64MiB 3,3V 16-bit",      0xC2, 0,  64, 0, LP_OPTIONS16},
+       {"NAND 64MiB 3,3V 16-bit",      0xC0, 0,  64, 0, LP_OPTIONS16},

        /* 1 Gigabit */
        {"NAND 128MiB 1,8V 8-bit",      0xA1, 0, 128, 0, LP_OPTIONS},
@@ -86,6 +90,7 @@ const struct nand_flash_dev nand_flash_ids[] = {
        {"NAND 128MiB 3,3V 8-bit",      0xD1, 0, 128, 0, LP_OPTIONS},
        {"NAND 128MiB 1,8V 16-bit",     0xB1, 0, 128, 0, LP_OPTIONS16},
        {"NAND 128MiB 3,3V 16-bit",     0xC1, 0, 128, 0, LP_OPTIONS16},
+       {"NAND 128MiB 1,8V 16-bit",     0xAD, 0, 128, 0, LP_OPTIONS16},

        /* 2 Gigabit */
        {"NAND 256MiB 1,8V 8-bit",      0xAA, 0, 256, 0, LP_OPTIONS},
@@ -111,6 +116,36 @@ const struct nand_flash_dev nand_flash_ids[] = {
        {"NAND 2GiB 1,8V 16-bit",       0xB5, 0, 2048, 0, LP_OPTIONS16},
        {"NAND 2GiB 3,3V 16-bit",       0xC5, 0, 2048, 0, LP_OPTIONS16},

+       /* 32 Gigabit */
+       {"NAND 4GiB 1,8V 8-bit",        0xA7, 0, 4096, 0, LP_OPTIONS},
+       {"NAND 4GiB 3,3V 8-bit",        0xD7, 0, 4096, 0, LP_OPTIONS},
+       {"NAND 4GiB 1,8V 16-bit",       0xB7, 0, 4096, 0, LP_OPTIONS16},
+       {"NAND 4GiB 3,3V 16-bit",       0xC7, 0, 4096, 0, LP_OPTIONS16},
+
+       /* 64 Gigabit */
+       {"NAND 8GiB 1,8V 8-bit",        0xAE, 0, 8192, 0, LP_OPTIONS},
+       {"NAND 8GiB 3,3V 8-bit",        0xDE, 0, 8192, 0, LP_OPTIONS},
+       {"NAND 8GiB 1,8V 16-bit",       0xBE, 0, 8192, 0, LP_OPTIONS16},
+       {"NAND 8GiB 3,3V 16-bit",       0xCE, 0, 8192, 0, LP_OPTIONS16},
+
+       /* 128 Gigabit */
+       {"NAND 16GiB 1,8V 8-bit",       0x1A, 0, 16384, 0, LP_OPTIONS},
+       {"NAND 16GiB 3,3V 8-bit",       0x3A, 0, 16384, 0, LP_OPTIONS},
+       {"NAND 16GiB 1,8V 16-bit",      0x2A, 0, 16384, 0, LP_OPTIONS16},
+       {"NAND 16GiB 3,3V 16-bit",      0x4A, 0, 16384, 0, LP_OPTIONS16},
+
+       /* 256 Gigabit */
+       {"NAND 32GiB 1,8V 8-bit",       0x1C, 0, 32768, 0, LP_OPTIONS},
+       {"NAND 32GiB 3,3V 8-bit",       0x3C, 0, 32768, 0, LP_OPTIONS},
+       {"NAND 32GiB 1,8V 16-bit",      0x2C, 0, 32768, 0, LP_OPTIONS16},
+       {"NAND 32GiB 3,3V 16-bit",      0x4C, 0, 32768, 0, LP_OPTIONS16},
+
+       /* 512 Gigabit */
+       {"NAND 64GiB 1,8V 8-bit",       0x1E, 0, 65536, 0, LP_OPTIONS},
+       {"NAND 64GiB 3,3V 8-bit",       0x3E, 0, 65536, 0, LP_OPTIONS},
+       {"NAND 64GiB 1,8V 16-bit",      0x2E, 0, 65536, 0, LP_OPTIONS16},
+       {"NAND 64GiB 3,3V 16-bit",      0x4E, 0, 65536, 0, LP_OPTIONS16},
+
        /*
         * Renesas AND 1 Gigabit. Those chips do not support extended id and
         * have a strange page/block layout !  The chosen minimum erasesize is
diff --git a/include/linux/bch.h b/include/linux/bch.h
new file mode 100644
index 0000000..295b4ef
--- /dev/null
+++ b/include/linux/bch.h
@@ -0,0 +1,79 @@
+/*
+ * Generic binary BCH encoding/decoding library
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright (c) 2011 Parrot S.A.
+ *
+ * Author: Ivan Djelic <ivan.djelic at parrot.com>
+ *
+ * Description:
+ *
+ * This library provides runtime configurable encoding/decoding of binary
+ * Bose-Chaudhuri-Hocquenghem (BCH) codes.
+*/
+#ifndef _BCH_H
+#define _BCH_H
+
+#include <linux/types.h>
+
+/**
+ * struct bch_control - BCH control structure
+ * @m:          Galois field order
+ * @n:          maximum codeword size in bits (= 2^m-1)
+ * @t:          error correction capability in bits
+ * @ecc_bits:   ecc exact size in bits, i.e. generator polynomial degree (<=m*t)
+ * @ecc_bytes:  ecc max size (m*t bits) in bytes
+ * @a_pow_tab:  Galois field GF(2^m) exponentiation lookup table
+ * @a_log_tab:  Galois field GF(2^m) log lookup table
+ * @mod8_tab:   remainder generator polynomial lookup tables
+ * @ecc_buf:    ecc parity words buffer
+ * @ecc_buf2:   ecc parity words buffer
+ * @xi_tab:     GF(2^m) base for solving degree 2 polynomial roots
+ * @syn:        syndrome buffer
+ * @cache:      log-based polynomial representation buffer
+ * @elp:        error locator polynomial
+ * @poly_2t:    temporary polynomials of degree 2t
+ */
+struct bch_control {
+       unsigned int    m;
+       unsigned int    n;
+       unsigned int    t;
+       unsigned int    ecc_bits;
+       unsigned int    ecc_bytes;
+/* private: */
+       uint16_t       *a_pow_tab;
+       uint16_t       *a_log_tab;
+       uint32_t       *mod8_tab;
+       uint32_t       *ecc_buf;
+       uint32_t       *ecc_buf2;
+       unsigned int   *xi_tab;
+       unsigned int   *syn;
+       int            *cache;
+       struct gf_poly *elp;
+       struct gf_poly *poly_2t[4];
+};
+
+struct bch_control *init_bch(int m, int t, unsigned int prim_poly);
+
+void free_bch(struct bch_control *bch);
+
+void encode_bch(struct bch_control *bch, const uint8_t *data,
+               unsigned int len, uint8_t *ecc);
+
+int decode_bch(struct bch_control *bch, const uint8_t *data, unsigned int len,
+              const uint8_t *recv_ecc, const uint8_t *calc_ecc,
+              const unsigned int *syn, unsigned int *errloc);
+
+#endif /* _BCH_H */
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 987a2ec..969fda1 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -18,13 +18,6 @@
 #ifndef __LINUX_MTD_NAND_H
 #define __LINUX_MTD_NAND_H

-/* XXX U-BOOT XXX */
-#if 0
-#include <linux/wait.h>
-#include <linux/spinlock.h>
-#include <linux/mtd/mtd.h>
-#endif
-
 #include "config.h"

 #include "linux/mtd/compat.h"
@@ -132,6 +125,7 @@ typedef enum {
        NAND_ECC_HW,
        NAND_ECC_HW_SYNDROME,
        NAND_ECC_HW_OOB_FIRST,
+       NAND_ECC_SOFT_BCH,
 } nand_ecc_modes_t;

 /*
@@ -308,6 +302,7 @@ struct nand_hw_control {
  * @prepad:    padding information for syndrome based ecc generators
  * @postpad:   padding information for syndrome based ecc generators
  * @layout:    ECC layout control struct pointer
+ * @priv:       pointer to private ecc control data
  * @hwctl:     function to control hardware ecc generator. Must only
  *             be provided if an hardware ECC is available
  * @calculate: function for ecc calculation or readback from ecc hardware
@@ -328,6 +323,7 @@ struct nand_ecc_ctrl {
        int                     prepad;
        int                     postpad;
        struct nand_ecclayout   *layout;
+       void                    *priv;
        void                    (*hwctl)(struct mtd_info *mtd, int mode);
        int                     (*calculate)(struct mtd_info *mtd,
                                             const uint8_t *dat,
diff --git a/include/linux/mtd/nand_bch.h b/include/linux/mtd/nand_bch.h
new file mode 100644
index 0000000..d8754dd
--- /dev/null
+++ b/include/linux/mtd/nand_bch.h
@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2011 Ivan Djelic <ivan.djelic at parrot.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This file is the header for the NAND BCH ECC implementation.
+ */
+
+#ifndef __MTD_NAND_BCH_H__
+#define __MTD_NAND_BCH_H__
+
+struct mtd_info;
+struct nand_bch_control;
+
+#if defined(CONFIG_NAND_ECC_BCH)
+
+static inline int mtd_nand_has_bch(void) { return 1; }
+
+/*
+ * Calculate BCH ecc code
+ */
+int nand_bch_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
+                          u_char *ecc_code);
+
+/*
+ * Detect and correct bit errors
+ */
+int nand_bch_correct_data(struct mtd_info *mtd, u_char *dat, u_char *read_ecc,
+                         u_char *calc_ecc);
+/*
+ * Initialize BCH encoder/decoder
+ */
+struct nand_bch_control *
+nand_bch_init(struct mtd_info *mtd, unsigned int eccsize,
+             unsigned int eccbytes, struct nand_ecclayout **ecclayout);
+/*
+ * Release BCH encoder/decoder resources
+ */
+void nand_bch_free(struct nand_bch_control *nbc);
+
+#else /* !CONFIG_NAND_ECC_BCH */
+
+static inline int mtd_nand_has_bch(void) { return 0; }
+
+static inline int
+nand_bch_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
+                      u_char *ecc_code)
+{
+       return -1;
+}
+
+static inline int
+nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
+                     unsigned char *read_ecc, unsigned char *calc_ecc)
+{
+       return -1;
+}
+
+static inline struct nand_bch_control *
+nand_bch_init(struct mtd_info *mtd, unsigned int eccsize,
+             unsigned int eccbytes, struct nand_ecclayout **ecclayout)
+{
+       return NULL;
+}
+
+static inline void nand_bch_free(struct nand_bch_control *nbc) {}
+
+#endif /* CONFIG_NAND_ECC_BCH */
+
+#endif /* __MTD_NAND_BCH_H__ */
diff --git a/lib/Makefile b/lib/Makefile
index 884f64c..46cc31a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -27,6 +27,7 @@ LIB   = $(obj)libgeneric.o

 ifndef CONFIG_SPL_BUILD
 COBJS-$(CONFIG_ADDR_MAP) += addr_map.o
+COBJS-$(CONFIG_BCH) += bch.o
 COBJS-$(CONFIG_BZIP2) += bzlib.o
 COBJS-$(CONFIG_BZIP2) += bzlib_crctable.o
 COBJS-$(CONFIG_BZIP2) += bzlib_decompress.o
diff --git a/lib/bch.c b/lib/bch.c
new file mode 100644
index 0000000..7f4ca92
--- /dev/null
+++ b/lib/bch.c
@@ -0,0 +1,1358 @@
+/*
+ * Generic binary BCH encoding/decoding library
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright (c) 2011 Parrot S.A.
+ *
+ * Author: Ivan Djelic <ivan.djelic at parrot.com>
+ *
+ * Description:
+ *
+ * This library provides runtime configurable encoding/decoding of binary
+ * Bose-Chaudhuri-Hocquenghem (BCH) codes.
+ *
+ * Call init_bch to get a pointer to a newly allocated bch_control structure for
+ * the given m (Galois field order), t (error correction capability) and
+ * (optional) primitive polynomial parameters.
+ *
+ * Call encode_bch to compute and store ecc parity bytes to a given buffer.
+ * Call decode_bch to detect and locate errors in received data.
+ *
+ * On systems supporting hw BCH features, intermediate results may be provided
+ * to decode_bch in order to skip certain steps. See decode_bch() documentation
+ * for details.
+ *
+ * Option CONFIG_BCH_CONST_PARAMS can be used to force fixed values of
+ * parameters m and t; thus allowing extra compiler optimizations and providing
+ * better (up to 2x) encoding performance. Using this option makes sense when
+ * (m,t) are fixed and known in advance, e.g. when using BCH error correction
+ * on a particular NAND flash device.
+ *
+ * Algorithmic details:
+ *
+ * Encoding is performed by processing 32 input bits in parallel, using 4
+ * remainder lookup tables.
+ *
+ * The final stage of decoding involves the following internal steps:
+ * a. Syndrome computation
+ * b. Error locator polynomial computation using Berlekamp-Massey algorithm
+ * c. Error locator root finding (by far the most expensive step)
+ *
+ * In this implementation, step c is not performed using the usual Chien search.
+ * Instead, an alternative approach described in [1] is used. It consists in
+ * factoring the error locator polynomial using the Berlekamp Trace algorithm
+ * (BTA) down to a certain degree (4), after which ad hoc low-degree polynomial
+ * solving techniques [2] are used. The resulting algorithm, called BTZ, yields
+ * much better performance than Chien search for usual (m,t) values (typically
+ * m >= 13, t < 32, see [1]).
+ *
+ * [1] B. Biswas, V. Herbert. Efficient root finding of polynomials over fields
+ * of characteristic 2, in: Western European Workshop on Research in Cryptology
+ * - WEWoRC 2009, Graz, Austria, LNCS, Springer, July 2009, to appear.
+ * [2] [Zin96] V.A. Zinoviev. On the solution of equations of degree 10 over
+ * finite fields GF(2^q). In Rapport de recherche INRIA no 2829, 1996.
+ */
+
+#include <common.h>
+#include <ubi_uboot.h>
+
+#include <linux/bitops.h>
+#include <asm/byteorder.h>
+#include <linux/bch.h>
+
+#if defined(CONFIG_BCH_CONST_PARAMS)
+#define GF_M(_p)               (CONFIG_BCH_CONST_M)
+#define GF_T(_p)               (CONFIG_BCH_CONST_T)
+#define GF_N(_p)               ((1 << (CONFIG_BCH_CONST_M))-1)
+#else
+#define GF_M(_p)               ((_p)->m)
+#define GF_T(_p)               ((_p)->t)
+#define GF_N(_p)               ((_p)->n)
+#endif
+
+#define BCH_ECC_WORDS(_p)      DIV_ROUND_UP(GF_M(_p)*GF_T(_p), 32)
+#define BCH_ECC_BYTES(_p)      DIV_ROUND_UP(GF_M(_p)*GF_T(_p), 8)
+
+#ifndef dbg
+#define dbg(_fmt, args...)     do {} while (0)
+#endif
+
+/*
+ * represent a polynomial over GF(2^m)
+ */
+struct gf_poly {
+       unsigned int deg;    /* polynomial degree */
+       unsigned int c[0];   /* polynomial terms */
+};
+
+/* given its degree, compute a polynomial size in bytes */
+#define GF_POLY_SZ(_d) (sizeof(struct gf_poly)+((_d)+1)*sizeof(unsigned int))
+
+/* polynomial of degree 1 */
+struct gf_poly_deg1 {
+       struct gf_poly poly;
+       unsigned int   c[2];
+};
+
+/*
+ * same as encode_bch(), but process input data one byte at a time
+ */
+static void encode_bch_unaligned(struct bch_control *bch,
+                                const unsigned char *data, unsigned int len,
+                                uint32_t *ecc)
+{
+       int i;
+       const uint32_t *p;
+       const int l = BCH_ECC_WORDS(bch)-1;
+
+       while (len--) {
+               p = bch->mod8_tab + (l+1)*(((ecc[0] >> 24)^(*data++)) & 0xff);
+
+               for (i = 0; i < l; i++)
+                       ecc[i] = ((ecc[i] << 8)|(ecc[i+1] >> 24))^(*p++);
+
+               ecc[l] = (ecc[l] << 8)^(*p);
+       }
+}
+
+/*
+ * convert ecc bytes to aligned, zero-padded 32-bit ecc words
+ */
+static void load_ecc8(struct bch_control *bch, uint32_t *dst,
+                     const uint8_t *src)
+{
+       uint8_t pad[4] = {0, 0, 0, 0};
+       unsigned int i, nwords = BCH_ECC_WORDS(bch)-1;
+
+       for (i = 0; i < nwords; i++, src += 4)
+               dst[i] = (src[0] << 24)|(src[1] << 16)|(src[2] << 8)|src[3];
+
+       memcpy(pad, src, BCH_ECC_BYTES(bch)-4*nwords);
+       dst[nwords] = (pad[0] << 24)|(pad[1] << 16)|(pad[2] << 8)|pad[3];
+}
+
+/*
+ * convert 32-bit ecc words to ecc bytes
+ */
+static void store_ecc8(struct bch_control *bch, uint8_t *dst,
+                      const uint32_t *src)
+{
+       uint8_t pad[4];
+       unsigned int i, nwords = BCH_ECC_WORDS(bch)-1;
+
+       for (i = 0; i < nwords; i++) {
+               *dst++ = (src[i] >> 24);
+               *dst++ = (src[i] >> 16) & 0xff;
+               *dst++ = (src[i] >>  8) & 0xff;
+               *dst++ = (src[i] >>  0) & 0xff;
+       }
+       pad[0] = (src[nwords] >> 24);
+       pad[1] = (src[nwords] >> 16) & 0xff;
+       pad[2] = (src[nwords] >>  8) & 0xff;
+       pad[3] = (src[nwords] >>  0) & 0xff;
+       memcpy(dst, pad, BCH_ECC_BYTES(bch)-4*nwords);
+}
+
+/**
+ * encode_bch - calculate BCH ecc parity of data
+ * @bch:   BCH control structure
+ * @data:  data to encode
+ * @len:   data length in bytes
+ * @ecc:   ecc parity data, must be initialized by caller
+ *
+ * The @ecc parity array is used both as input and output parameter, in order to
+ * allow incremental computations. It should be of the size indicated by member
+ * @ecc_bytes of @bch, and should be initialized to 0 before the first call.
+ *
+ * The exact number of computed ecc parity bits is given by member @ecc_bits of
+ * @bch; it may be less than m*t for large values of t.
+ */
+void encode_bch(struct bch_control *bch, const uint8_t *data,
+               unsigned int len, uint8_t *ecc)
+{
+       const unsigned int l = BCH_ECC_WORDS(bch)-1;
+       unsigned int i, mlen;
+       unsigned long m;
+       uint32_t w, r[l+1];
+       const uint32_t * const tab0 = bch->mod8_tab;
+       const uint32_t * const tab1 = tab0 + 256*(l+1);
+       const uint32_t * const tab2 = tab1 + 256*(l+1);
+       const uint32_t * const tab3 = tab2 + 256*(l+1);
+       const uint32_t *pdata, *p0, *p1, *p2, *p3;
+
+       if (ecc) {
+               /* load ecc parity bytes into internal 32-bit buffer */
+               load_ecc8(bch, bch->ecc_buf, ecc);
+       } else {
+               memset(bch->ecc_buf, 0, sizeof(r));
+       }
+
+       /* process first unaligned data bytes */
+       m = ((unsigned long)data) & 3;
+       if (m) {
+               mlen = (len < (4-m)) ? len : 4-m;
+               encode_bch_unaligned(bch, data, mlen, bch->ecc_buf);
+               data += mlen;
+               len  -= mlen;
+       }
+
+       /* process 32-bit aligned data words */
+       pdata = (uint32_t *)data;
+       mlen  = len/4;
+       data += 4*mlen;
+       len  -= 4*mlen;
+       memcpy(r, bch->ecc_buf, sizeof(r));
+
+       /*
+        * split each 32-bit word into 4 polynomials of weight 8 as follows:
+        *
+        * 31 ...24  23 ...16  15 ... 8  7 ... 0
+        * xxxxxxxx  yyyyyyyy  zzzzzzzz  tttttttt
+        *                               tttttttt  mod g = r0 (precomputed)
+        *                     zzzzzzzz  00000000  mod g = r1 (precomputed)
+        *           yyyyyyyy  00000000  00000000  mod g = r2 (precomputed)
+        * xxxxxxxx  00000000  00000000  00000000  mod g = r3 (precomputed)
+        * xxxxxxxx  yyyyyyyy  zzzzzzzz  tttttttt  mod g = r0^r1^r2^r3
+        */
+       while (mlen--) {
+               /* input data is read in big-endian format */
+               w = r[0]^cpu_to_be32(*pdata++);
+               p0 = tab0 + (l+1)*((w >>  0) & 0xff);
+               p1 = tab1 + (l+1)*((w >>  8) & 0xff);
+               p2 = tab2 + (l+1)*((w >> 16) & 0xff);
+               p3 = tab3 + (l+1)*((w >> 24) & 0xff);
+
+               for (i = 0; i < l; i++)
+                       r[i] = r[i+1]^p0[i]^p1[i]^p2[i]^p3[i];
+
+               r[l] = p0[l]^p1[l]^p2[l]^p3[l];
+       }
+       memcpy(bch->ecc_buf, r, sizeof(r));
+
+       /* process last unaligned bytes */
+       if (len)
+               encode_bch_unaligned(bch, data, len, bch->ecc_buf);
+
+       /* store ecc parity bytes into original parity buffer */
+       if (ecc)
+               store_ecc8(bch, ecc, bch->ecc_buf);
+}
+
+static inline int modulo(struct bch_control *bch, unsigned int v)
+{
+       const unsigned int n = GF_N(bch);
+       while (v >= n) {
+               v -= n;
+               v = (v & n) + (v >> GF_M(bch));
+       }
+       return v;
+}
+
+/*
+ * shorter and faster modulo function, only works when v < 2N.
+ */
+static inline int mod_s(struct bch_control *bch, unsigned int v)
+{
+       const unsigned int n = GF_N(bch);
+       return (v < n) ? v : v-n;
+}
+
+static inline int deg(unsigned int poly)
+{
+       /* polynomial degree is the most-significant bit index */
+       return fls(poly)-1;
+}
+
+static inline int parity(unsigned int x)
+{
+       /*
+        * public domain code snippet, lifted from
+        * http://www-graphics.stanford.edu/~seander/bithacks.html
+        */
+       x ^= x >> 1;
+       x ^= x >> 2;
+       x = (x & 0x11111111U) * 0x11111111U;
+       return (x >> 28) & 1;
+}
+
+/* Galois field basic operations: multiply, divide, inverse, etc. */
+
+static inline unsigned int gf_mul(struct bch_control *bch, unsigned int a,
+                                 unsigned int b)
+{
+       return (a && b) ? bch->a_pow_tab[mod_s(bch, bch->a_log_tab[a]+
+                                              bch->a_log_tab[b])] : 0;
+}
+
+static inline unsigned int gf_sqr(struct bch_control *bch, unsigned int a)
+{
+       return a ? bch->a_pow_tab[mod_s(bch, 2*bch->a_log_tab[a])] : 0;
+}
+
+static inline unsigned int gf_div(struct bch_control *bch, unsigned int a,
+                                 unsigned int b)
+{
+       return a ? bch->a_pow_tab[mod_s(bch, bch->a_log_tab[a]+
+                                       GF_N(bch)-bch->a_log_tab[b])] : 0;
+}
+
+static inline unsigned int gf_inv(struct bch_control *bch, unsigned int a)
+{
+       return bch->a_pow_tab[GF_N(bch)-bch->a_log_tab[a]];
+}
+
+static inline unsigned int a_pow(struct bch_control *bch, int i)
+{
+       return bch->a_pow_tab[modulo(bch, i)];
+}
+
+static inline int a_log(struct bch_control *bch, unsigned int x)
+{
+       return bch->a_log_tab[x];
+}
+
+static inline int a_ilog(struct bch_control *bch, unsigned int x)
+{
+       return mod_s(bch, GF_N(bch)-bch->a_log_tab[x]);
+}
+
+/*
+ * compute 2t syndromes of ecc polynomial, i.e. ecc(a^j) for j=1..2t
+ */
+static void compute_syndromes(struct bch_control *bch, uint32_t *ecc,
+                             unsigned int *syn)
+{
+       int i, j, s;
+       unsigned int m;
+       uint32_t poly;
+       const int t = GF_T(bch);
+
+       s = bch->ecc_bits;
+
+       /* make sure extra bits in last ecc word are cleared */
+       m = ((unsigned int)s) & 31;
+       if (m)
+               ecc[s/32] &= ~((1u << (32-m))-1);
+       memset(syn, 0, 2*t*sizeof(*syn));
+
+       /* compute v(a^j) for j=1 .. 2t-1 */
+       do {
+               poly = *ecc++;
+               s -= 32;
+               while (poly) {
+                       i = deg(poly);
+                       for (j = 0; j < 2*t; j += 2)
+                               syn[j] ^= a_pow(bch, (j+1)*(i+s));
+
+                       poly ^= (1 << i);
+               }
+       } while (s > 0);
+
+       /* v(a^(2j)) = v(a^j)^2 */
+       for (j = 0; j < t; j++)
+               syn[2*j+1] = gf_sqr(bch, syn[j]);
+}
+
+static void gf_poly_copy(struct gf_poly *dst, struct gf_poly *src)
+{
+       memcpy(dst, src, GF_POLY_SZ(src->deg));
+}
+
+static int compute_error_locator_polynomial(struct bch_control *bch,
+                                           const unsigned int *syn)
+{
+       const unsigned int t = GF_T(bch);
+       const unsigned int n = GF_N(bch);
+       unsigned int i, j, tmp, l, pd = 1, d = syn[0];
+       struct gf_poly *elp = bch->elp;
+       struct gf_poly *pelp = bch->poly_2t[0];
+       struct gf_poly *elp_copy = bch->poly_2t[1];
+       int k, pp = -1;
+
+       memset(pelp, 0, GF_POLY_SZ(2*t));
+       memset(elp, 0, GF_POLY_SZ(2*t));
+
+       pelp->deg = 0;
+       pelp->c[0] = 1;
+       elp->deg = 0;
+       elp->c[0] = 1;
+
+       /* use simplified binary Berlekamp-Massey algorithm */
+       for (i = 0; (i < t) && (elp->deg <= t); i++) {
+               if (d) {
+                       k = 2*i-pp;
+                       gf_poly_copy(elp_copy, elp);
+                       /* e[i+1](X) = e[i](X)+di*dp^-1*X^2(i-p)*e[p](X) */
+                       tmp = a_log(bch, d)+n-a_log(bch, pd);
+                       for (j = 0; j <= pelp->deg; j++) {
+                               if (pelp->c[j]) {
+                                       l = a_log(bch, pelp->c[j]);
+                                       elp->c[j+k] ^= a_pow(bch, tmp+l);
+                               }
+                       }
+                       /* compute l[i+1] = max(l[i]->c[l[p]+2*(i-p]) */
+                       tmp = pelp->deg+k;
+                       if (tmp > elp->deg) {
+                               elp->deg = tmp;
+                               gf_poly_copy(pelp, elp_copy);
+                               pd = d;
+                               pp = 2*i;
+                       }
+               }
+               /* di+1 = S(2i+3)+elp[i+1].1*S(2i+2)+...+elp[i+1].lS(2i+3-l) */
+               if (i < t-1) {
+                       d = syn[2*i+2];
+                       for (j = 1; j <= elp->deg; j++)
+                               d ^= gf_mul(bch, elp->c[j], syn[2*i+2-j]);
+               }
+       }
+       dbg("elp=%s\n", gf_poly_str(elp));
+       return (elp->deg > t) ? -1 : (int)elp->deg;
+}
+
+/*
+ * solve a m x m linear system in GF(2) with an expected number of solutions,
+ * and return the number of found solutions
+ */
+static int solve_linear_system(struct bch_control *bch, unsigned int *rows,
+                              unsigned int *sol, int nsol)
+{
+       const int m = GF_M(bch);
+       unsigned int tmp, mask;
+       int rem, c, r, p, k, param[m];
+
+       k = 0;
+       mask = 1 << m;
+
+       /* Gaussian elimination */
+       for (c = 0; c < m; c++) {
+               rem = 0;
+               p = c-k;
+               /* find suitable row for elimination */
+               for (r = p; r < m; r++) {
+                       if (rows[r] & mask) {
+                               if (r != p) {
+                                       tmp = rows[r];
+                                       rows[r] = rows[p];
+                                       rows[p] = tmp;
+                               }
+                               rem = r+1;
+                               break;
+                       }
+               }
+               if (rem) {
+                       /* perform elimination on remaining rows */
+                       tmp = rows[p];
+                       for (r = rem; r < m; r++) {
+                               if (rows[r] & mask)
+                                       rows[r] ^= tmp;
+                       }
+               } else {
+                       /* elimination not needed, store defective row index */
+                       param[k++] = c;
+               }
+               mask >>= 1;
+       }
+       /* rewrite system, inserting fake parameter rows */
+       if (k > 0) {
+               p = k;
+               for (r = m-1; r >= 0; r--) {
+                       if ((r > m-1-k) && rows[r])
+                               /* system has no solution */
+                               return 0;
+
+                       rows[r] = (p && (r == param[p-1])) ?
+                               p--, 1u << (m-r) : rows[r-p];
+               }
+       }
+
+       if (nsol != (1 << k))
+               /* unexpected number of solutions */
+               return 0;
+
+       for (p = 0; p < nsol; p++) {
+               /* set parameters for p-th solution */
+               for (c = 0; c < k; c++)
+                       rows[param[c]] = (rows[param[c]] & ~1)|((p >> c) & 1);
+
+               /* compute unique solution */
+               tmp = 0;
+               for (r = m-1; r >= 0; r--) {
+                       mask = rows[r] & (tmp|1);
+                       tmp |= parity(mask) << (m-r);
+               }
+               sol[p] = tmp >> 1;
+       }
+       return nsol;
+}
+
+/*
+ * this function builds and solves a linear system for finding roots of a degree
+ * 4 affine monic polynomial X^4+aX^2+bX+c over GF(2^m).
+ */
+static int find_affine4_roots(struct bch_control *bch, unsigned int a,
+                             unsigned int b, unsigned int c,
+                             unsigned int *roots)
+{
+       int i, j, k;
+       const int m = GF_M(bch);
+       unsigned int mask = 0xff, t, rows[16] = {0,};
+
+       j = a_log(bch, b);
+       k = a_log(bch, a);
+       rows[0] = c;
+
+       /* buid linear system to solve X^4+aX^2+bX+c = 0 */
+       for (i = 0; i < m; i++) {
+               rows[i+1] = bch->a_pow_tab[4*i]^
+                       (a ? bch->a_pow_tab[mod_s(bch, k)] : 0)^
+                       (b ? bch->a_pow_tab[mod_s(bch, j)] : 0);
+               j++;
+               k += 2;
+       }
+       /*
+        * transpose 16x16 matrix before passing it to linear solver
+        * warning: this code assumes m < 16
+        */
+       for (j = 8; j != 0; j >>= 1, mask ^= (mask << j)) {
+               for (k = 0; k < 16; k = (k+j+1) & ~j) {
+                       t = ((rows[k] >> j)^rows[k+j]) & mask;
+                       rows[k] ^= (t << j);
+                       rows[k+j] ^= t;
+               }
+       }
+       return solve_linear_system(bch, rows, roots, 4);
+}
+
+/*
+ * compute root r of a degree 1 polynomial over GF(2^m) (returned as log(1/r))
+ */
+static int find_poly_deg1_roots(struct bch_control *bch, struct gf_poly *poly,
+                               unsigned int *roots)
+{
+       int n = 0;
+
+       if (poly->c[0])
+               /* poly[X] = bX+c with c!=0, root=c/b */
+               roots[n++] = mod_s(bch, GF_N(bch)-bch->a_log_tab[poly->c[0]]+
+                                  bch->a_log_tab[poly->c[1]]);
+       return n;
+}
+
+/*
+ * compute roots of a degree 2 polynomial over GF(2^m)
+ */
+static int find_poly_deg2_roots(struct bch_control *bch, struct gf_poly *poly,
+                               unsigned int *roots)
+{
+       int n = 0, i, l0, l1, l2;
+       unsigned int u, v, r;
+
+       if (poly->c[0] && poly->c[1]) {
+
+               l0 = bch->a_log_tab[poly->c[0]];
+               l1 = bch->a_log_tab[poly->c[1]];
+               l2 = bch->a_log_tab[poly->c[2]];
+
+               /* using z=a/bX, transform aX^2+bX+c into z^2+z+u (u=ac/b^2) */
+               u = a_pow(bch, l0+l2+2*(GF_N(bch)-l1));
+               /*
+                * let u = sum(li.a^i) i=0..m-1; then compute r = sum(li.xi):
+                * r^2+r = sum(li.(xi^2+xi)) = sum(li.(a^i+Tr(a^i).a^k)) =
+                * u + sum(li.Tr(a^i).a^k) = u+a^k.Tr(sum(li.a^i)) = u+a^k.Tr(u)
+                * i.e. r and r+1 are roots iff Tr(u)=0
+                */
+               r = 0;
+               v = u;
+               while (v) {
+                       i = deg(v);
+                       r ^= bch->xi_tab[i];
+                       v ^= (1 << i);
+               }
+               /* verify root */
+               if ((gf_sqr(bch, r)^r) == u) {
+                       /* reverse z=a/bX transformation and compute log(1/r) */
+                       roots[n++] = modulo(bch, 2*GF_N(bch)-l1-
+                                           bch->a_log_tab[r]+l2);
+                       roots[n++] = modulo(bch, 2*GF_N(bch)-l1-
+                                           bch->a_log_tab[r^1]+l2);
+               }
+       }
+       return n;
+}
+
+/*
+ * compute roots of a degree 3 polynomial over GF(2^m)
+ */
+static int find_poly_deg3_roots(struct bch_control *bch, struct gf_poly *poly,
+                               unsigned int *roots)
+{
+       int i, n = 0;
+       unsigned int a, b, c, a2, b2, c2, e3, tmp[4];
+
+       if (poly->c[0]) {
+               /* transform polynomial into monic X^3 + a2X^2 + b2X + c2 */
+               e3 = poly->c[3];
+               c2 = gf_div(bch, poly->c[0], e3);
+               b2 = gf_div(bch, poly->c[1], e3);
+               a2 = gf_div(bch, poly->c[2], e3);
+
+               /* (X+a2)(X^3+a2X^2+b2X+c2) = X^4+aX^2+bX+c (affine) */
+               c = gf_mul(bch, a2, c2);           /* c = a2c2      */
+               b = gf_mul(bch, a2, b2)^c2;        /* b = a2b2 + c2 */
+               a = gf_sqr(bch, a2)^b2;            /* a = a2^2 + b2 */
+
+               /* find the 4 roots of this affine polynomial */
+               if (find_affine4_roots(bch, a, b, c, tmp) == 4) {
+                       /* remove a2 from final list of roots */
+                       for (i = 0; i < 4; i++) {
+                               if (tmp[i] != a2)
+                                       roots[n++] = a_ilog(bch, tmp[i]);
+                       }
+               }
+       }
+       return n;
+}
+
+/*
+ * compute roots of a degree 4 polynomial over GF(2^m)
+ */
+static int find_poly_deg4_roots(struct bch_control *bch, struct gf_poly *poly,
+                               unsigned int *roots)
+{
+       int i, l, n = 0;
+       unsigned int a, b, c, d, e = 0, f, a2, b2, c2, e4;
+
+       if (poly->c[0] == 0)
+               return 0;
+
+       /* transform polynomial into monic X^4 + aX^3 + bX^2 + cX + d */
+       e4 = poly->c[4];
+       d = gf_div(bch, poly->c[0], e4);
+       c = gf_div(bch, poly->c[1], e4);
+       b = gf_div(bch, poly->c[2], e4);
+       a = gf_div(bch, poly->c[3], e4);
+
+       /* use Y=1/X transformation to get an affine polynomial */
+       if (a) {
+               /* first, eliminate cX by using z=X+e with ae^2+c=0 */
+               if (c) {
+                       /* compute e such that e^2 = c/a */
+                       f = gf_div(bch, c, a);
+                       l = a_log(bch, f);
+                       l += (l & 1) ? GF_N(bch) : 0;
+                       e = a_pow(bch, l/2);
+                       /*
+                        * use transformation z=X+e:
+                        * z^4+e^4 + a(z^3+ez^2+e^2z+e^3) + b(z^2+e^2) +cz+ce+d
+                        * z^4 + az^3 + (ae+b)z^2 + (ae^2+c)z+e^4+be^2+ae^3+ce+d
+                        * z^4 + az^3 + (ae+b)z^2 + e^4+be^2+d
+                        * z^4 + az^3 +     b'z^2 + d'
+                        */
+                       d = a_pow(bch, 2*l)^gf_mul(bch, b, f)^d;
+                       b = gf_mul(bch, a, e)^b;
+               }
+               /* now, use Y=1/X to get Y^4 + b/dY^2 + a/dY + 1/d */
+               if (d == 0)
+                       /* assume all roots have multiplicity 1 */
+                       return 0;
+
+               c2 = gf_inv(bch, d);
+               b2 = gf_div(bch, a, d);
+               a2 = gf_div(bch, b, d);
+       } else {
+               /* polynomial is already affine */
+               c2 = d;
+               b2 = c;
+               a2 = b;
+       }
+       /* find the 4 roots of this affine polynomial */
+       if (find_affine4_roots(bch, a2, b2, c2, roots) == 4) {
+               for (i = 0; i < 4; i++) {
+                       /* post-process roots (reverse transformations) */
+                       f = a ? gf_inv(bch, roots[i]) : roots[i];
+                       roots[i] = a_ilog(bch, f^e);
+               }
+               n = 4;
+       }
+       return n;
+}
+
+/*
+ * build monic, log-based representation of a polynomial
+ */
+static void gf_poly_logrep(struct bch_control *bch,
+                          const struct gf_poly *a, int *rep)
+{
+       int i, d = a->deg, l = GF_N(bch)-a_log(bch, a->c[a->deg]);
+
+       /* represent 0 values with -1; warning, rep[d] is not set to 1 */
+       for (i = 0; i < d; i++)
+               rep[i] = a->c[i] ? mod_s(bch, a_log(bch, a->c[i])+l) : -1;
+}
+
+/*
+ * compute polynomial Euclidean division remainder in GF(2^m)[X]
+ */
+static void gf_poly_mod(struct bch_control *bch, struct gf_poly *a,
+                       const struct gf_poly *b, int *rep)
+{
+       int la, p, m;
+       unsigned int i, j, *c = a->c;
+       const unsigned int d = b->deg;
+
+       if (a->deg < d)
+               return;
+
+       /* reuse or compute log representation of denominator */
+       if (!rep) {
+               rep = bch->cache;
+               gf_poly_logrep(bch, b, rep);
+       }
+
+       for (j = a->deg; j >= d; j--) {
+               if (c[j]) {
+                       la = a_log(bch, c[j]);
+                       p = j-d;
+                       for (i = 0; i < d; i++, p++) {
+                               m = rep[i];
+                               if (m >= 0)
+                                       c[p] ^= bch->a_pow_tab[mod_s(bch,
+                                                                    m+la)];
+                       }
+               }
+       }
+       a->deg = d-1;
+       while (!c[a->deg] && a->deg)
+               a->deg--;
+}
+
+/*
+ * compute polynomial Euclidean division quotient in GF(2^m)[X]
+ */
+static void gf_poly_div(struct bch_control *bch, struct gf_poly *a,
+                       const struct gf_poly *b, struct gf_poly *q)
+{
+       if (a->deg >= b->deg) {
+               q->deg = a->deg-b->deg;
+               /* compute a mod b (modifies a) */
+               gf_poly_mod(bch, a, b, NULL);
+               /* quotient is stored in upper part of polynomial a */
+               memcpy(q->c, &a->c[b->deg], (1+q->deg)*sizeof(unsigned int));
+       } else {
+               q->deg = 0;
+               q->c[0] = 0;
+       }
+}
+
+/*
+ * compute polynomial GCD (Greatest Common Divisor) in GF(2^m)[X]
+ */
+static struct gf_poly *gf_poly_gcd(struct bch_control *bch, struct gf_poly *a,
+                                  struct gf_poly *b)
+{
+       struct gf_poly *tmp;
+
+       dbg("gcd(%s,%s)=", gf_poly_str(a), gf_poly_str(b));
+
+       if (a->deg < b->deg) {
+               tmp = b;
+               b = a;
+               a = tmp;
+       }
+
+       while (b->deg > 0) {
+               gf_poly_mod(bch, a, b, NULL);
+               tmp = b;
+               b = a;
+               a = tmp;
+       }
+
+       dbg("%s\n", gf_poly_str(a));
+
+       return a;
+}
+
+/*
+ * Given a polynomial f and an integer k, compute Tr(a^kX) mod f
+ * This is used in Berlekamp Trace algorithm for splitting polynomials
+ */
+static void compute_trace_bk_mod(struct bch_control *bch, int k,
+                                const struct gf_poly *f, struct gf_poly *z,
+                                struct gf_poly *out)
+{
+       const int m = GF_M(bch);
+       int i, j;
+
+       /* z contains z^2j mod f */
+       z->deg = 1;
+       z->c[0] = 0;
+       z->c[1] = bch->a_pow_tab[k];
+
+       out->deg = 0;
+       memset(out, 0, GF_POLY_SZ(f->deg));
+
+       /* compute f log representation only once */
+       gf_poly_logrep(bch, f, bch->cache);
+
+       for (i = 0; i < m; i++) {
+               /* add a^(k*2^i)(z^(2^i) mod f) and compute (z^(2^i) mod f)^2 */
+               for (j = z->deg; j >= 0; j--) {
+                       out->c[j] ^= z->c[j];
+                       z->c[2*j] = gf_sqr(bch, z->c[j]);
+                       z->c[2*j+1] = 0;
+               }
+               if (z->deg > out->deg)
+                       out->deg = z->deg;
+
+               if (i < m-1) {
+                       z->deg *= 2;
+                       /* z^(2(i+1)) mod f = (z^(2^i) mod f)^2 mod f */
+                       gf_poly_mod(bch, z, f, bch->cache);
+               }
+       }
+       while (!out->c[out->deg] && out->deg)
+               out->deg--;
+
+       dbg("Tr(a^%d.X) mod f = %s\n", k, gf_poly_str(out));
+}
+
+/*
+ * factor a polynomial using Berlekamp Trace algorithm (BTA)
+ */
+static void factor_polynomial(struct bch_control *bch, int k, struct gf_poly *f,
+                             struct gf_poly **g, struct gf_poly **h)
+{
+       struct gf_poly *f2 = bch->poly_2t[0];
+       struct gf_poly *q  = bch->poly_2t[1];
+       struct gf_poly *tk = bch->poly_2t[2];
+       struct gf_poly *z  = bch->poly_2t[3];
+       struct gf_poly *gcd;
+
+       dbg("factoring %s...\n", gf_poly_str(f));
+
+       *g = f;
+       *h = NULL;
+
+       /* tk = Tr(a^k.X) mod f */
+       compute_trace_bk_mod(bch, k, f, z, tk);
+
+       if (tk->deg > 0) {
+               /* compute g = gcd(f, tk) (destructive operation) */
+               gf_poly_copy(f2, f);
+               gcd = gf_poly_gcd(bch, f2, tk);
+               if (gcd->deg < f->deg) {
+                       /* compute h=f/gcd(f,tk); this will modify f and q */
+                       gf_poly_div(bch, f, gcd, q);
+                       /* store g and h in-place (clobbering f) */
+                       *h = &((struct gf_poly_deg1 *)f)[gcd->deg].poly;
+                       gf_poly_copy(*g, gcd);
+                       gf_poly_copy(*h, q);
+               }
+       }
+}
+
+/*
+ * find roots of a polynomial, using BTZ algorithm; see the beginning of this
+ * file for details
+ */
+static int find_poly_roots(struct bch_control *bch, unsigned int k,
+                          struct gf_poly *poly, unsigned int *roots)
+{
+       int cnt;
+       struct gf_poly *f1, *f2;
+
+       switch (poly->deg) {
+               /* handle low degree polynomials with ad hoc techniques */
+       case 1:
+               cnt = find_poly_deg1_roots(bch, poly, roots);
+               break;
+       case 2:
+               cnt = find_poly_deg2_roots(bch, poly, roots);
+               break;
+       case 3:
+               cnt = find_poly_deg3_roots(bch, poly, roots);
+               break;
+       case 4:
+               cnt = find_poly_deg4_roots(bch, poly, roots);
+               break;
+       default:
+               /* factor polynomial using Berlekamp Trace Algorithm (BTA) */
+               cnt = 0;
+               if (poly->deg && (k <= GF_M(bch))) {
+                       factor_polynomial(bch, k, poly, &f1, &f2);
+                       if (f1)
+                               cnt += find_poly_roots(bch, k+1, f1, roots);
+                       if (f2)
+                               cnt += find_poly_roots(bch, k+1, f2, roots+cnt);
+               }
+               break;
+       }
+       return cnt;
+}
+
+#if defined(USE_CHIEN_SEARCH)
+/*
+ * exhaustive root search (Chien) implementation - not used, included only for
+ * reference/comparison tests
+ */
+static int chien_search(struct bch_control *bch, unsigned int len,
+                       struct gf_poly *p, unsigned int *roots)
+{
+       int m;
+       unsigned int i, j, syn, syn0, count = 0;
+       const unsigned int k = 8*len+bch->ecc_bits;
+
+       /* use a log-based representation of polynomial */
+       gf_poly_logrep(bch, p, bch->cache);
+       bch->cache[p->deg] = 0;
+       syn0 = gf_div(bch, p->c[0], p->c[p->deg]);
+
+       for (i = GF_N(bch)-k+1; i <= GF_N(bch); i++) {
+               /* compute elp(a^i) */
+               for (j = 1, syn = syn0; j <= p->deg; j++) {
+                       m = bch->cache[j];
+                       if (m >= 0)
+                               syn ^= a_pow(bch, m+j*i);
+               }
+               if (syn == 0) {
+                       roots[count++] = GF_N(bch)-i;
+                       if (count == p->deg)
+                               break;
+               }
+       }
+       return (count == p->deg) ? count : 0;
+}
+#define find_poly_roots(_p, _k, _elp, _loc) chien_search(_p, len, _elp, _loc)
+#endif /* USE_CHIEN_SEARCH */
+
+/**
+ * decode_bch - decode received codeword and find bit error locations
+ * @bch:      BCH control structure
+ * @data:     received data, ignored if @calc_ecc is provided
+ * @len:      data length in bytes, must always be provided
+ * @recv_ecc: received ecc, if NULL then assume it was XORed in @calc_ecc
+ * @calc_ecc: calculated ecc, if NULL then calc_ecc is computed from @data
+ * @syn:      hw computed syndrome data (if NULL, syndrome is calculated)
+ * @errloc:   output array of error locations
+ *
+ * Returns:
+ *  The number of errors found, or -EBADMSG if decoding failed, or -EINVAL if
+ *  invalid parameters were provided
+ *
+ * Depending on the available hw BCH support and the need to compute @calc_ecc
+ * separately (using encode_bch()), this function should be called with one of
+ * the following parameter configurations -
+ *
+ * by providing @data and @recv_ecc only:
+ *   decode_bch(@bch, @data, @len, @recv_ecc, NULL, NULL, @errloc)
+ *
+ * by providing @recv_ecc and @calc_ecc:
+ *   decode_bch(@bch, NULL, @len, @recv_ecc, @calc_ecc, NULL, @errloc)
+ *
+ * by providing ecc = recv_ecc XOR calc_ecc:
+ *   decode_bch(@bch, NULL, @len, NULL, ecc, NULL, @errloc)
+ *
+ * by providing syndrome results @syn:
+ *   decode_bch(@bch, NULL, @len, NULL, NULL, @syn, @errloc)
+ *
+ * Once decode_bch() has successfully returned with a positive value, error
+ * locations returned in array @errloc should be interpreted as follows -
+ *
+ * if (errloc[n] >= 8*len), then n-th error is located in ecc (no need for
+ * data correction)
+ *
+ * if (errloc[n] < 8*len), then n-th error is located in data and can be
+ * corrected with statement data[errloc[n]/8] ^= 1 << (errloc[n] % 8);
+ *
+ * Note that this function does not perform any data correction by itself, it
+ * merely indicates error locations.
+ */
+int decode_bch(struct bch_control *bch, const uint8_t *data, unsigned int len,
+              const uint8_t *recv_ecc, const uint8_t *calc_ecc,
+              const unsigned int *syn, unsigned int *errloc)
+{
+       const unsigned int ecc_words = BCH_ECC_WORDS(bch);
+       unsigned int nbits;
+       int i, err, nroots;
+       uint32_t sum;
+
+       /* sanity check: make sure data length can be handled */
+       if (8*len > (bch->n-bch->ecc_bits))
+               return -EINVAL;
+
+       /* if caller does not provide syndromes, compute them */
+       if (!syn) {
+               if (!calc_ecc) {
+                       /* compute received data ecc into an internal buffer */
+                       if (!data || !recv_ecc)
+                               return -EINVAL;
+                       encode_bch(bch, data, len, NULL);
+               } else {
+                       /* load provided calculated ecc */
+                       load_ecc8(bch, bch->ecc_buf, calc_ecc);
+               }
+               /* load received ecc or assume it was XORed in calc_ecc */
+               if (recv_ecc) {
+                       load_ecc8(bch, bch->ecc_buf2, recv_ecc);
+                       /* XOR received and calculated ecc */
+                       for (i = 0, sum = 0; i < (int)ecc_words; i++) {
+                               bch->ecc_buf[i] ^= bch->ecc_buf2[i];
+                               sum |= bch->ecc_buf[i];
+                       }
+                       if (!sum)
+                               /* no error found */
+                               return 0;
+               }
+               compute_syndromes(bch, bch->ecc_buf, bch->syn);
+               syn = bch->syn;
+       }
+
+       err = compute_error_locator_polynomial(bch, syn);
+       if (err > 0) {
+               nroots = find_poly_roots(bch, 1, bch->elp, errloc);
+               if (err != nroots)
+                       err = -1;
+       }
+       if (err > 0) {
+               /* post-process raw error locations for easier correction */
+               nbits = (len*8)+bch->ecc_bits;
+               for (i = 0; i < err; i++) {
+                       if (errloc[i] >= nbits) {
+                               err = -1;
+                               break;
+                       }
+                       errloc[i] = nbits-1-errloc[i];
+                       errloc[i] = (errloc[i] & ~7)|(7-(errloc[i] & 7));
+               }
+       }
+       return (err >= 0) ? err : -EBADMSG;
+}
+
+/*
+ * generate Galois field lookup tables
+ */
+static int build_gf_tables(struct bch_control *bch, unsigned int poly)
+{
+       unsigned int i, x = 1;
+       const unsigned int k = 1 << deg(poly);
+
+       /* primitive polynomial must be of degree m */
+       if (k != (1u << GF_M(bch)))
+               return -1;
+
+       for (i = 0; i < GF_N(bch); i++) {
+               bch->a_pow_tab[i] = x;
+               bch->a_log_tab[x] = i;
+               if (i && (x == 1))
+                       /* polynomial is not primitive (a^i=1 with 0<i<2^m-1) */
+                       return -1;
+               x <<= 1;
+               if (x & k)
+                       x ^= poly;
+       }
+       bch->a_pow_tab[GF_N(bch)] = 1;
+       bch->a_log_tab[0] = 0;
+
+       return 0;
+}
+
+/*
+ * compute generator polynomial remainder tables for fast encoding
+ */
+static void build_mod8_tables(struct bch_control *bch, const uint32_t *g)
+{
+       int i, j, b, d;
+       uint32_t data, hi, lo, *tab;
+       const int l = BCH_ECC_WORDS(bch);
+       const int plen = DIV_ROUND_UP(bch->ecc_bits+1, 32);
+       const int ecclen = DIV_ROUND_UP(bch->ecc_bits, 32);
+
+       memset(bch->mod8_tab, 0, 4*256*l*sizeof(*bch->mod8_tab));
+
+       for (i = 0; i < 256; i++) {
+               /* p(X)=i is a small polynomial of weight <= 8 */
+               for (b = 0; b < 4; b++) {
+                       /* we want to compute (p(X).X^(8*b+deg(g))) mod g(X) */
+                       tab = bch->mod8_tab + (b*256+i)*l;
+                       data = i << (8*b);
+                       while (data) {
+                               d = deg(data);
+                               /* subtract X^d.g(X) from p(X).X^(8*b+deg(g)) */
+                               data ^= g[0] >> (31-d);
+                               for (j = 0; j < ecclen; j++) {
+                                       hi = (d < 31) ? g[j] << (d+1) : 0;
+                                       lo = (j+1 < plen) ?
+                                               g[j+1] >> (31-d) : 0;
+                                       tab[j] ^= hi|lo;
+                               }
+                       }
+               }
+       }
+}
+
+/*
+ * build a base for factoring degree 2 polynomials
+ */
+static int build_deg2_base(struct bch_control *bch)
+{
+       const int m = GF_M(bch);
+       int i, j, r;
+       unsigned int sum, x, y, remaining, ak = 0, xi[m];
+
+       /* find k s.t. Tr(a^k) = 1 and 0 <= k < m */
+       for (i = 0; i < m; i++) {
+               for (j = 0, sum = 0; j < m; j++)
+                       sum ^= a_pow(bch, i*(1 << j));
+
+               if (sum) {
+                       ak = bch->a_pow_tab[i];
+                       break;
+               }
+       }
+       /* find xi, i=0..m-1 such that xi^2+xi = a^i+Tr(a^i).a^k */
+       remaining = m;
+       memset(xi, 0, sizeof(xi));
+
+       for (x = 0; (x <= GF_N(bch)) && remaining; x++) {
+               y = gf_sqr(bch, x)^x;
+               for (i = 0; i < 2; i++) {
+                       r = a_log(bch, y);
+                       if (y && (r < m) && !xi[r]) {
+                               bch->xi_tab[r] = x;
+                               xi[r] = 1;
+                               remaining--;
+                               dbg("x%d = %x\n", r, x);
+                               break;
+                       }
+                       y ^= ak;
+               }
+       }
+       /* should not happen but check anyway */
+       return remaining ? -1 : 0;
+}
+
+static void *bch_alloc(size_t size, int *err)
+{
+       void *ptr;
+
+       ptr = kmalloc(size, GFP_KERNEL);
+       if (ptr == NULL)
+               *err = 1;
+       return ptr;
+}
+
+/*
+ * compute generator polynomial for given (m,t) parameters.
+ */
+static uint32_t *compute_generator_polynomial(struct bch_control *bch)
+{
+       const unsigned int m = GF_M(bch);
+       const unsigned int t = GF_T(bch);
+       int n, err = 0;
+       unsigned int i, j, nbits, r, word, *roots;
+       struct gf_poly *g;
+       uint32_t *genpoly;
+
+       g = bch_alloc(GF_POLY_SZ(m*t), &err);
+       roots = bch_alloc((bch->n+1)*sizeof(*roots), &err);
+       genpoly = bch_alloc(DIV_ROUND_UP(m*t+1, 32)*sizeof(*genpoly), &err);
+
+       if (err) {
+               kfree(genpoly);
+               genpoly = NULL;
+               goto finish;
+       }
+
+       /* enumerate all roots of g(X) */
+       memset(roots , 0, (bch->n+1)*sizeof(*roots));
+       for (i = 0; i < t; i++) {
+               for (j = 0, r = 2*i+1; j < m; j++) {
+                       roots[r] = 1;
+                       r = mod_s(bch, 2*r);
+               }
+       }
+       /* build generator polynomial g(X) */
+       g->deg = 0;
+       g->c[0] = 1;
+       for (i = 0; i < GF_N(bch); i++) {
+               if (roots[i]) {
+                       /* multiply g(X) by (X+root) */
+                       r = bch->a_pow_tab[i];
+                       g->c[g->deg+1] = 1;
+                       for (j = g->deg; j > 0; j--)
+                               g->c[j] = gf_mul(bch, g->c[j], r)^g->c[j-1];
+
+                       g->c[0] = gf_mul(bch, g->c[0], r);
+                       g->deg++;
+               }
+       }
+       /* store left-justified binary representation of g(X) */
+       n = g->deg+1;
+       i = 0;
+
+       while (n > 0) {
+               nbits = (n > 32) ? 32 : n;
+               for (j = 0, word = 0; j < nbits; j++) {
+                       if (g->c[n-1-j])
+                               word |= 1u << (31-j);
+               }
+               genpoly[i++] = word;
+               n -= nbits;
+       }
+       bch->ecc_bits = g->deg;
+
+finish:
+       kfree(g);
+       kfree(roots);
+
+       return genpoly;
+}
+
+/**
+ * init_bch - initialize a BCH encoder/decoder
+ * @m:          Galois field order, should be in the range 5-15
+ * @t:          maximum error correction capability, in bits
+ * @prim_poly:  user-provided primitive polynomial (or 0 to use default)
+ *
+ * Returns:
+ *  a newly allocated BCH control structure if successful, NULL otherwise
+ *
+ * This initialization can take some time, as lookup tables are built for fast
+ * encoding/decoding; make sure not to call this function from a time critical
+ * path. Usually, init_bch() should be called on module/driver init and
+ * free_bch() should be called to release memory on exit.
+ *
+ * You may provide your own primitive polynomial of degree @m in argument
+ * @prim_poly, or let init_bch() use its default polynomial.
+ *
+ * Once init_bch() has successfully returned a pointer to a newly allocated
+ * BCH control structure, ecc length in bytes is given by member @ecc_bytes of
+ * the structure.
+ */
+struct bch_control *init_bch(int m, int t, unsigned int prim_poly)
+{
+       int err = 0;
+       unsigned int i, words;
+       uint32_t *genpoly;
+       struct bch_control *bch = NULL;
+
+       const int min_m = 5;
+       const int max_m = 15;
+
+       /* default primitive polynomials */
+       static const unsigned int prim_poly_tab[] = {
+               0x25, 0x43, 0x83, 0x11d, 0x211, 0x409, 0x805, 0x1053, 0x201b,
+               0x402b, 0x8003,
+       };
+
+#if defined(CONFIG_BCH_CONST_PARAMS)
+       if ((m != (CONFIG_BCH_CONST_M)) || (t != (CONFIG_BCH_CONST_T))) {
+               printk(KERN_ERR "bch encoder/decoder was configured to support "
+                      "parameters m=%d, t=%d only!\n",
+                      CONFIG_BCH_CONST_M, CONFIG_BCH_CONST_T);
+               goto fail;
+       }
+#endif
+       if ((m < min_m) || (m > max_m))
+               /*
+                * values of m greater than 15 are not currently supported;
+                * supporting m > 15 would require changing table base type
+                * (uint16_t) and a small patch in matrix transposition
+                */
+               goto fail;
+
+       /* sanity checks */
+       if ((t < 1) || (m*t >= ((1 << m)-1)))
+               /* invalid t value */
+               goto fail;
+
+       /* select a primitive polynomial for generating GF(2^m) */
+       if (prim_poly == 0)
+               prim_poly = prim_poly_tab[m-min_m];
+
+       bch = kzalloc(sizeof(*bch), GFP_KERNEL);
+       if (bch == NULL)
+               goto fail;
+
+       bch->m = m;
+       bch->t = t;
+       bch->n = (1 << m)-1;
+       words  = DIV_ROUND_UP(m*t, 32);
+       bch->ecc_bytes = DIV_ROUND_UP(m*t, 8);
+       bch->a_pow_tab = bch_alloc((1+bch->n)*sizeof(*bch->a_pow_tab), &err);
+       bch->a_log_tab = bch_alloc((1+bch->n)*sizeof(*bch->a_log_tab), &err);
+       bch->mod8_tab  = bch_alloc(words*1024*sizeof(*bch->mod8_tab), &err);
+       bch->ecc_buf   = bch_alloc(words*sizeof(*bch->ecc_buf), &err);
+       bch->ecc_buf2  = bch_alloc(words*sizeof(*bch->ecc_buf2), &err);
+       bch->xi_tab    = bch_alloc(m*sizeof(*bch->xi_tab), &err);
+       bch->syn       = bch_alloc(2*t*sizeof(*bch->syn), &err);
+       bch->cache     = bch_alloc(2*t*sizeof(*bch->cache), &err);
+       bch->elp       = bch_alloc((t+1)*sizeof(struct gf_poly_deg1), &err);
+
+       for (i = 0; i < ARRAY_SIZE(bch->poly_2t); i++)
+               bch->poly_2t[i] = bch_alloc(GF_POLY_SZ(2*t), &err);
+
+       if (err)
+               goto fail;
+
+       err = build_gf_tables(bch, prim_poly);
+       if (err)
+               goto fail;
+
+       /* use generator polynomial for computing encoding tables */
+       genpoly = compute_generator_polynomial(bch);
+       if (genpoly == NULL)
+               goto fail;
+
+       build_mod8_tables(bch, genpoly);
+       kfree(genpoly);
+
+       err = build_deg2_base(bch);
+       if (err)
+               goto fail;
+
+       return bch;
+
+fail:
+       free_bch(bch);
+       return NULL;
+}
+
+/**
+ *  free_bch - free the BCH control structure
+ *  @bch:    BCH control structure to release
+ */
+void free_bch(struct bch_control *bch)
+{
+       unsigned int i;
+
+       if (bch) {
+               kfree(bch->a_pow_tab);
+               kfree(bch->a_log_tab);
+               kfree(bch->mod8_tab);
+               kfree(bch->ecc_buf);
+               kfree(bch->ecc_buf2);
+               kfree(bch->xi_tab);
+               kfree(bch->syn);
+               kfree(bch->cache);
+               kfree(bch->elp);
+
+               for (i = 0; i < ARRAY_SIZE(bch->poly_2t); i++)
+                       kfree(bch->poly_2t[i]);
+
+               kfree(bch);
+       }
+}
--
1.7.4.1



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