[PATCH v3 2/8] lib/bch: Allow easy bit swapping

[Miquel Raynal <miquel.raynal@xxxxxxxxxxx>]

From: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>

It seems that several hardware ECC engine use a swapped representation
of bytes compared to software. It means that when the software BCH
engine is working in conjunction with data generated with hardware, we
must swap the bits inside bytes, eg:

    0x0A = b0000_1010 -> b0101_0000 = 0x50

Make it possible just by flipping a boolean in the BCH control
structure.

Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
Cc: Ivan Djelic <ivan.djelic@xxxxxxxxxx>
---
 include/linux/bch.h |  1 +
 lib/bch.c           | 84 ++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 72 insertions(+), 13 deletions(-)

diff --git a/include/linux/bch.h b/include/linux/bch.h
index 9c35e7cd5890..c42f50cacfdc 100644
--- a/include/linux/bch.h
+++ b/include/linux/bch.h
@@ -51,6 +51,7 @@ 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);
diff --git a/lib/bch.c b/lib/bch.c
index 1091841ac716..81bf8b426eea 100644
--- 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 +291,12 @@ 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++);
+		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 +1104,9 @@ 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;
-- 
2.20.1


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