[PATCH 2/2] imx-bbu-nand-fcb: add support for imx6ul

[Jan Remmet <j.remmet@phytec.de>]

imx6ul secure the fcb with bch 40. The imx-kobs tool use a own modified
bch lib. They reverse the bit order of the data and the ecc.
To use the bch lib in barebox the bytes in the data buffers must be
reversed.
The data layout on nand is bit aligned. But with 40 bits this is not an
issue for imx6ul now.

Signed-off-by: Jan Remmet <j.remmet@phytec.de>
---
 common/Kconfig            |   1 +
 common/imx-bbu-nand-fcb.c | 145 +++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 143 insertions(+), 3 deletions(-)

diff --git a/common/Kconfig b/common/Kconfig
index ed472a0..a10caf6 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -101,6 +101,7 @@ config BAREBOX_UPDATE_IMX_NAND_FCB
 	depends on BAREBOX_UPDATE
 	depends on MTD_WRITE
 	depends on NAND_MXS
+	select BCH if ARCH_IMX6
 	default y
 
 config UBIFORMAT
diff --git a/common/imx-bbu-nand-fcb.c b/common/imx-bbu-nand-fcb.c
index 34a5f83..5d3d3f7 100644
--- a/common/imx-bbu-nand-fcb.c
+++ b/common/imx-bbu-nand-fcb.c
@@ -33,9 +33,12 @@
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/nand.h>
 #include <linux/stat.h>
+#include <linux/bch.h>
+#include <linux/bitops.h>
 #include <io.h>
 #include <crc.h>
 #include <mach/generic.h>
+#include <mach/imx6.h>
 #include <mtd/mtd-peb.h>
 
 struct dbbt_block {
@@ -129,6 +132,132 @@ static uint8_t calculate_parity_13_8(uint8_t d)
 	return p;
 }
 
+static uint8_t reverse_bit(uint8_t b)
+{
+	b = (b & 0xf0) >> 4 | (b & 0x0f) << 4;
+	b = (b & 0xcc) >> 2 | (b & 0x33) << 2;
+	b = (b & 0xaa) >> 1 | (b & 0x55) << 1;
+
+	return b;
+}
+
+static void encode_bch_ecc(void *buf, struct fcb_block *fcb, int eccbits)
+{
+	int i, j, m = 13;
+	int blocksize = 128;
+	int numblocks = 8;
+	int ecc_buf_size = (m * eccbits + 7) / 8;
+	struct bch_control *bch = init_bch(m, eccbits, 0);
+	uint8_t *ecc_buf = xmalloc(ecc_buf_size);
+	uint8_t *tmp_buf = xzalloc(blocksize * numblocks);
+	uint8_t *psrc, *pdst;
+
+	/*
+	 * The blocks here are bit aligned. If eccbits is a multiple of 8,
+	 * we just can copy bytes. Otherwiese we must move the blocks to
+	 * the next free bit position.
+	 */
+	BUG_ON(eccbits % 8);
+
+	memcpy(tmp_buf, fcb, sizeof(*fcb));
+
+	for (i = 0; i < numblocks; i++) {
+		memset(ecc_buf, 0, ecc_buf_size);
+		psrc = tmp_buf + i * blocksize;
+		pdst = buf + i * (blocksize + ecc_buf_size);
+
+		/* copy data byte aligned to destination buf */
+		memcpy(pdst, psrc, blocksize);
+
+		/*
+		 * imx-kobs use a modified encode_bch which reverse the
+		 * bit order of the data before calculating bch.
+		 * Do this in the buffer and use the bch lib here.
+		 */
+		for (j = 0; j < blocksize; j++)
+			psrc[j] = reverse_bit(psrc[j]);
+
+		encode_bch(bch, psrc, blocksize, ecc_buf);
+
+		/* reverse ecc bit */
+		for (j = 0; j < ecc_buf_size; j++)
+			ecc_buf[j] = reverse_bit(ecc_buf[j]);
+
+		/* Here eccbuf is byte aligned and we can just copy it */
+		memcpy(pdst + blocksize, ecc_buf, ecc_buf_size);
+	}
+
+	free(ecc_buf);
+	free(tmp_buf);
+	free_bch(bch);
+}
+
+struct fcb_block *read_fcb_bch(void *rawpage, int eccbits)
+{
+	int i, j, ret, errbit, m = 13;
+	int blocksize = 128;
+	int numblocks = 8;
+	int ecc_buf_size = (m * eccbits + 7) / 8;
+	struct bch_control *bch = init_bch(m, eccbits, 0);
+	uint8_t *fcb = xmalloc(numblocks * blocksize);
+	uint8_t *ecc_buf = xmalloc(ecc_buf_size);
+	uint8_t *data_buf = xmalloc(blocksize);
+	unsigned int *errloc = xmalloc(eccbits * sizeof(*errloc));
+	uint8_t *psrc, *pdst;
+
+	/* see encode_bch_ecc */
+	BUG_ON(eccbits % 8);
+
+	for (i = 0; i < numblocks; i++) {
+		psrc = rawpage + 32 + i * (blocksize + ecc_buf_size);
+		pdst = fcb + i * blocksize;
+
+		/* reverse data bit */
+		for (j = 0; j < blocksize; j++)
+			data_buf[j] = reverse_bit(psrc[j]);
+
+		/* reverse ecc bit */
+		for (j = 0; j < ecc_buf_size; j++)
+			ecc_buf[j] = reverse_bit(psrc[j + blocksize]);
+
+		ret = decode_bch(bch, data_buf, blocksize, ecc_buf,
+				 NULL, NULL, errloc);
+
+		if (ret < 0) {
+			pr_err("Uncorrectable error at block %d\n", i);
+			free(fcb);
+			fcb = ERR_PTR(ret);
+			goto out;
+		}
+		if (ret > 0)
+			pr_info("Found %d correctable errors in block %d\n",
+				ret, i);
+
+		for (j = 0; j < ret; j++) {
+			/*
+			 * calculate the reverse position
+			 * pos - (pos % 8) -> byte offset
+			 * 7 - (pos % 8) -> reverse bit position
+			 */
+			errbit = errloc[j] - 2 * (errloc[j] % 8) + 7;
+			pr_debug("Found error: bit %d in block %d\n",
+				 errbit, i);
+			if (errbit < blocksize * 8)
+				change_bit(errbit, psrc);
+			/* else error in ecc, ignore it */
+		}
+		memcpy(pdst, psrc, blocksize);
+	}
+
+out:
+	free(data_buf);
+	free(ecc_buf);
+	free(errloc);
+	free_bch(bch);
+
+	return (struct fcb_block *)fcb;
+}
+
 static void encode_hamming_13_8(void *_src, void *_ecc, size_t size)
 {
 	int i;
@@ -312,7 +441,11 @@ static int read_fcb(struct mtd_info *mtd, int num, struct fcb_block **retfcb)
 		goto err;
 	}
 
-	fcb = read_fcb_hamming_13_8(rawpage);
+	if (cpu_is_mx6ul())
+		fcb = read_fcb_bch(rawpage, 40);
+	else
+		fcb = read_fcb_hamming_13_8(rawpage);
+
 	if (IS_ERR(fcb)) {
 		pr_err("Cannot read fcb\n");
 		ret = PTR_ERR(fcb);
@@ -766,8 +899,14 @@ static int imx_bbu_write_fcbs_dbbts(struct mtd_info *mtd, struct fcb_block *fcb)
 
 	fcb_raw_page = xzalloc(mtd->writesize + mtd->oobsize);
 
-	memcpy(fcb_raw_page + 12, fcb, sizeof(struct fcb_block));
-	encode_hamming_13_8(fcb_raw_page + 12, fcb_raw_page + 12 + 512, 512);
+	if (cpu_is_mx6ul()) {
+		/* 40 bit BCH, for i.MX6UL */
+		encode_bch_ecc(fcb_raw_page + 32, fcb, 40);
+	} else {
+		memcpy(fcb_raw_page + 12, fcb, sizeof(struct fcb_block));
+		encode_hamming_13_8(fcb_raw_page + 12,
+				    fcb_raw_page + 12 + 512, 512);
+	}
 
 	dbbt = dbbt_data_create(mtd);
 
-- 
2.7.4


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