lib/bch: Allow easy bit swapping

It seems that several hardware ECC engine use a swapped representation
of bytes compared to software. This might having to do with how the
ECC engine is wired to the NAND controller or the order the bits are
passed to the hardware BCH logic.

This means that when the software BCH engine is working in conjunction
with data generated with hardware, sometimes we might need to swap the
bits inside bytes, eg:

    0x0A = b0000_1010 -> b0101_0000 = 0x50

Make it possible by adding a boolean to the BCH initialization routine.

Regarding the implementation itself, this is a rather simple approach
that can probably be enhanced in the future by preparing the
->a_{mod,pow}_tab tables with the swapping in mind.

Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200519074549.23673-3-miquel.raynal@bootlin.com

diff --git a/drivers/mtd/devices/docg3.c b/drivers/mtd/devices/docg3.c
index 799df8d03357359c74296352470f39a72cc68c15..a030792115bc2e9bfd14ac48ab76b76e997b3de7 100644 (file)
--- a/drivers/mtd/devices/docg3.c
+++ b/drivers/mtd/devices/docg3.c
@@ -1985,7 +1985,7 @@ static int __init docg3_probe(struct platform_device *pdev)
        cascade->base = base;
        mutex_init(&cascade->lock);
        cascade->bch = bch_init(DOC_ECC_BCH_M, DOC_ECC_BCH_T,
-                               DOC_ECC_BCH_PRIMPOLY);
+                               DOC_ECC_BCH_PRIMPOLY, false);
        if (!cascade->bch)
                return ret;
 

diff --git a/drivers/mtd/nand/raw/nand_bch.c b/drivers/mtd/nand/raw/nand_bch.c
index d95fcc7358e9711b401504d73402481a71a70341..d5af8c5fd02f7ecb13bb536e8f7b6a991e534444 100644 (file)
--- a/drivers/mtd/nand/raw/nand_bch.c
+++ b/drivers/mtd/nand/raw/nand_bch.c
@@ -130,7 +130,7 @@ struct nand_bch_control *nand_bch_init(struct mtd_info *mtd)
        if (!nbc)
                goto fail;
 
-       nbc->bch = bch_init(m, t, 0);
+       nbc->bch = bch_init(m, t, 0, false);
        if (!nbc->bch)
                goto fail;
 

diff --git a/include/linux/bch.h b/include/linux/bch.h
index 9c35e7cd5890993a4c923296ce69b41531586da6..85fdce83d4e213e9c6b20af6641ae788fa089a82 100644 (file)
--- a/include/linux/bch.h
+++ b/include/linux/bch.h
@@ -33,6 +33,7 @@
  * @cache:      log-based polynomial representation buffer
  * @elp:        error locator polynomial
  * @poly_2t:    temporary polynomials of degree 2t
+ * @swap_bits:  swap bits within data and syndrome bytes
  */
 struct bch_control {
        unsigned int    m;
@@ -51,9 +52,11 @@ struct bch_control {
        int            *cache;
        struct gf_poly *elp;
        struct gf_poly *poly_2t[4];
+       bool            swap_bits;
 };
 
-struct bch_control *bch_init(int m, int t, unsigned int prim_poly);
+struct bch_control *bch_init(int m, int t, unsigned int prim_poly,
+                            bool swap_bits);
 
 void bch_free(struct bch_control *bch);
 

diff --git a/lib/bch.c b/lib/bch.c
index 1091841ac7160f204185fe966de1310ef0a2b32b..7c031ee8b93b2515612ed1e2aafb2a905c57bc50 100644 (file)
--- a/lib/bch.c
+++ b/lib/bch.c
@@ -114,6 +114,49 @@ struct gf_poly_deg1 {
        unsigned int   c[2];
 };
 
+static u8 swap_bits_table[] = {
+       0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
+       0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
+       0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
+       0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
+       0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
+       0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
+       0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
+       0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
+       0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
+       0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
+       0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
+       0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
+       0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
+       0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
+       0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
+       0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
+       0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
+       0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
+       0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
+       0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
+       0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
+       0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
+       0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
+       0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
+       0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
+       0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
+       0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
+       0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
+       0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
+       0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
+       0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
+       0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
+};
+
+static u8 swap_bits(struct bch_control *bch, u8 in)
+{
+       if (!bch->swap_bits)
+               return in;
+
+       return swap_bits_table[in];
+}
+
 /*
  * same as bch_encode(), but process input data one byte at a time
  */
@@ -126,7 +169,9 @@ static void bch_encode_unaligned(struct bch_control *bch,
        const int l = BCH_ECC_WORDS(bch)-1;
 
        while (len--) {
-               p = bch->mod8_tab + (l+1)*(((ecc[0] >> 24)^(*data++)) & 0xff);
+               u8 tmp = swap_bits(bch, *data++);
+
+               p = bch->mod8_tab + (l+1)*(((ecc[0] >> 24)^(tmp)) & 0xff);
 
                for (i = 0; i < l; i++)
                        ecc[i] = ((ecc[i] << 8)|(ecc[i+1] >> 24))^(*p++);
@@ -145,10 +190,16 @@ static void load_ecc8(struct bch_control *bch, uint32_t *dst,
        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];
+               dst[i] = ((u32)swap_bits(bch, src[0]) << 24) |
+                       ((u32)swap_bits(bch, src[1]) << 16) |
+                       ((u32)swap_bits(bch, src[2]) << 8) |
+                       swap_bits(bch, src[3]);
 
        memcpy(pad, src, BCH_ECC_BYTES(bch)-4*nwords);
-       dst[nwords] = (pad[0] << 24)|(pad[1] << 16)|(pad[2] << 8)|pad[3];
+       dst[nwords] = ((u32)swap_bits(bch, pad[0]) << 24) |
+               ((u32)swap_bits(bch, pad[1]) << 16) |
+               ((u32)swap_bits(bch, pad[2]) << 8) |
+               swap_bits(bch, pad[3]);
 }
 
 /*
@@ -161,15 +212,15 @@ static void store_ecc8(struct bch_control *bch, uint8_t *dst,
        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;
+               *dst++ = swap_bits(bch, src[i] >> 24);
+               *dst++ = swap_bits(bch, src[i] >> 16);
+               *dst++ = swap_bits(bch, src[i] >> 8);
+               *dst++ = swap_bits(bch, src[i]);
        }
-       pad[0] = (src[nwords] >> 24);
-       pad[1] = (src[nwords] >> 16) & 0xff;
-       pad[2] = (src[nwords] >>  8) & 0xff;
-       pad[3] = (src[nwords] >>  0) & 0xff;
+       pad[0] = swap_bits(bch, src[nwords] >> 24);
+       pad[1] = swap_bits(bch, src[nwords] >> 16);
+       pad[2] = swap_bits(bch, src[nwords] >> 8);
+       pad[3] = swap_bits(bch, src[nwords]);
        memcpy(dst, pad, BCH_ECC_BYTES(bch)-4*nwords);
 }
 
@@ -240,7 +291,13 @@ void bch_encode(struct bch_control *bch, const uint8_t *data,
         */
        while (mlen--) {
                /* input data is read in big-endian format */
-               w = r[0]^cpu_to_be32(*pdata++);
+               w = cpu_to_be32(*pdata++);
+               if (bch->swap_bits)
+                       w = (u32)swap_bits(bch, w) |
+                           ((u32)swap_bits(bch, w >> 8) << 8) |
+                           ((u32)swap_bits(bch, w >> 16) << 16) |
+                           ((u32)swap_bits(bch, w >> 24) << 24);
+               w ^= r[0];
                p0 = tab0 + (l+1)*((w >>  0) & 0xff);
                p1 = tab1 + (l+1)*((w >>  8) & 0xff);
                p2 = tab2 + (l+1)*((w >> 16) & 0xff);
@@ -1048,7 +1105,9 @@ int bch_decode(struct bch_control *bch, const uint8_t *data, unsigned int len,
                                break;
                        }
                        errloc[i] = nbits-1-errloc[i];
-                       errloc[i] = (errloc[i] & ~7)|(7-(errloc[i] & 7));
+                       if (!bch->swap_bits)
+                               errloc[i] = (errloc[i] & ~7) |
+                                           (7-(errloc[i] & 7));
                }
        }
        return (err >= 0) ? err : -EBADMSG;
@@ -1240,6 +1299,7 @@ finish:
  * @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)
+ * @swap_bits:  swap bits within data and syndrome bytes
  *
  * Returns:
  *  a newly allocated BCH control structure if successful, NULL otherwise
@@ -1256,7 +1316,8 @@ finish:
  * BCH control structure, ecc length in bytes is given by member @ecc_bytes of
  * the structure.
  */
-struct bch_control *bch_init(int m, int t, unsigned int prim_poly)
+struct bch_control *bch_init(int m, int t, unsigned int prim_poly,
+                            bool swap_bits)
 {
        int err = 0;
        unsigned int i, words;
@@ -1321,6 +1382,7 @@ struct bch_control *bch_init(int m, int t, unsigned int prim_poly)
        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);
+       bch->swap_bits = swap_bits;
 
        for (i = 0; i < ARRAY_SIZE(bch->poly_2t); i++)
                bch->poly_2t[i] = bch_alloc(GF_POLY_SZ(2*t), &err);