[PATCH v6 2/6] mtd: nand: vf610_nfc: add hardware BCH-ECC support

Stefan Agner
2015-06-18T22:58:35Z

This adds hardware ECC support using the BCH encoder in the NFC IP.
The ECC encoder supports up to 32-bit correction by using 60 error
correction bytes. There is no sub-page ECC step, ECC is calculated
always accross the whole page (up to 2k pages). Raw writes writes
are possible through the common nand_write_page_raw implementation,
however raw reads are not possible since the hardware ECC mode need
to be enabled at command time.

Signed-off-by: Bill Pringlemeir <bpringlemeir@nbsps.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>
---
drivers/mtd/nand/Kconfig | 6 +-
drivers/mtd/nand/vf610_nfc.c | 201 ++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 204 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
index 9ceac79..944e588 100644
--- a/drivers/mtd/nand/Kconfig
+++ b/drivers/mtd/nand/Kconfig
@@ -472,8 +472,10 @@ config MTD_NAND_VF610_NFC
help
Enables support for NAND Flash Controller on some Freescale
processors like the VF610, MPC5125, MCF54418 or Kinetis K70.
- The driver supports a maximum 2k page size. The driver
- currently does not support hardware ECC.
+ The driver supports a maximum 2k page size. With 2k pages and
+ 64 bytes or more of OOB, hardware ECC with up to 32-bit error
+ correction is supported. Hardware ECC is only enabled through
+ device tree.

config MTD_NAND_MXC
tristate "MXC NAND support"
diff --git a/drivers/mtd/nand/vf610_nfc.c b/drivers/mtd/nand/vf610_nfc.c
index 0da500e..4d795a5 100644
--- a/drivers/mtd/nand/vf610_nfc.c
+++ b/drivers/mtd/nand/vf610_nfc.c
@@ -19,6 +19,8 @@
* - Untested on MPC5125 and M54418.
* - DMA not used.
* - 2K pages or less.
+ * - Only 2K page w. 64+ OOB and hardware ECC.
+ * - Raw page reads not implemented when using ECC.
*/

#include <linux/module.h>
@@ -72,6 +74,8 @@

/* NFC ECC mode define */
#define ECC_BYPASS 0
+#define ECC_45_BYTE 6
+#define ECC_60_BYTE 7

/*** Register Mask and bit definitions */

@@ -104,6 +108,8 @@
#define STATUS_BYTE1_MASK 0x000000FF

/* NFC_FLASH_CONFIG Field */
+#define CONFIG_ECC_SRAM_ADDR_MASK 0x7FC00000
+#define CONFIG_ECC_SRAM_ADDR_SHIFT 22
#define CONFIG_ECC_SRAM_REQ_BIT (1<<21)
#define CONFIG_DMA_REQ_BIT (1<<20)
#define CONFIG_ECC_MODE_MASK 0x000E0000
@@ -122,6 +128,21 @@
#define CMD_DONE_CLEAR_BIT (1<<18)
#define IDLE_CLEAR_BIT (1<<17)

+/* ECC status placed at end of buffers. */
+#define ECC_SRAM_ADDR ((PAGE_2K + 256 - 8) >> 3)
+#define ECC_STATUS_MASK 0x80
+#define ECC_ERR_COUNT 0x3F
+
+/*
+ * ECC status is stored at NFC_CFG[ECCADD] +4 for little-endian
+ * and +7 for big-endian SoCs.
+ */
+#ifdef __LITTLE_ENDIAN
+#define ECC_OFFSET 4
+#else
+#define ECC_OFFSET 7
+#endif
+
struct vf610_nfc {
struct mtd_info mtd;
struct nand_chip chip;
@@ -136,10 +157,40 @@ struct vf610_nfc {
#define ALT_BUF_STAT 2
#define ALT_BUF_ONFI 3
struct clk *clk;
+ bool use_hw_ecc;
+ u32 ecc_mode;
};

#define mtd_to_nfc(_mtd) container_of(_mtd, struct vf610_nfc, mtd)

+static struct nand_ecclayout vf610_nfc_ecc45 = {
+ .eccbytes = 45,
+ .eccpos = {19, 20, 21, 22, 23,
+ 24, 25, 26, 27, 28, 29, 30, 31,
+ 32, 33, 34, 35, 36, 37, 38, 39,
+ 40, 41, 42, 43, 44, 45, 46, 47,
+ 48, 49, 50, 51, 52, 53, 54, 55,
+ 56, 57, 58, 59, 60, 61, 62, 63},
+ .oobfree = {
+ {.offset = 2,
+ .length = 17} }
+};
+
+static struct nand_ecclayout vf610_nfc_ecc60 = {
+ .eccbytes = 60,
+ .eccpos = { 4, 5, 6, 7, 8, 9, 10, 11,
+ 12, 13, 14, 15, 16, 17, 18, 19,
+ 20, 21, 22, 23, 24, 25, 26, 27,
+ 28, 29, 30, 31, 32, 33, 34, 35,
+ 36, 37, 38, 39, 40, 41, 42, 43,
+ 44, 45, 46, 47, 48, 49, 50, 51,
+ 52, 53, 54, 55, 56, 57, 58, 59,
+ 60, 61, 62, 63 },
+ .oobfree = {
+ {.offset = 2,
+ .length = 2} }
+};
+
static inline u32 vf610_nfc_read(struct vf610_nfc *nfc, uint reg)
{
return readl(nfc->regs + reg);
@@ -281,6 +332,13 @@ static void vf610_nfc_addr_cycle(struct vf610_nfc *nfc, int column, int page)
ROW_ADDR_SHIFT, page);
}

+static inline void vf610_nfc_ecc_mode(struct vf610_nfc *nfc, int ecc_mode)
+{
+ vf610_nfc_set_field(nfc, NFC_FLASH_CONFIG,
+ CONFIG_ECC_MODE_MASK,
+ CONFIG_ECC_MODE_SHIFT, ecc_mode);
+}
+
static inline void vf610_nfc_transfer_size(struct vf610_nfc *nfc, int size)
{
vf610_nfc_write(nfc, NFC_SECTOR_SIZE, size);
@@ -299,13 +357,20 @@ static void vf610_nfc_command(struct mtd_info *mtd, unsigned command,
case NAND_CMD_SEQIN:
/* Use valid column/page from preread... */
vf610_nfc_addr_cycle(nfc, column, page);
+ nfc->buf_offset = 0;
+
/*
* SEQIN => data => PAGEPROG sequence is done by the controller
* hence we do not need to issue the command here...
*/
return;
case NAND_CMD_PAGEPROG:
- page_sz += mtd->writesize + mtd->oobsize;
+ page_sz += nfc->page_sz;
+ if (nfc->use_hw_ecc)
+ vf610_nfc_ecc_mode(nfc, nfc->ecc_mode);
+ else
+ vf610_nfc_ecc_mode(nfc, ECC_BYPASS);
+
vf610_nfc_transfer_size(nfc, page_sz);
vf610_nfc_send_commands(nfc, NAND_CMD_SEQIN,
command, PROGRAM_PAGE_CMD_CODE);
@@ -323,11 +388,13 @@ static void vf610_nfc_command(struct mtd_info *mtd, unsigned command,
vf610_nfc_send_commands(nfc, NAND_CMD_READ0,
NAND_CMD_READSTART, READ_PAGE_CMD_CODE);
vf610_nfc_addr_cycle(nfc, column, page);
+ vf610_nfc_ecc_mode(nfc, ECC_BYPASS);
break;

case NAND_CMD_READ0:
page_sz += mtd->writesize + mtd->oobsize;
vf610_nfc_transfer_size(nfc, page_sz);
+ vf610_nfc_ecc_mode(nfc, nfc->ecc_mode);
vf610_nfc_send_commands(nfc, NAND_CMD_READ0,
NAND_CMD_READSTART, READ_PAGE_CMD_CODE);
vf610_nfc_addr_cycle(nfc, column, page);
@@ -339,6 +406,7 @@ static void vf610_nfc_command(struct mtd_info *mtd, unsigned command,
vf610_nfc_send_command(nfc, command, READ_ONFI_PARAM_CMD_CODE);
vf610_nfc_set_field(nfc, NFC_ROW_ADDR, ROW_ADDR_MASK,
ROW_ADDR_SHIFT, column);
+ vf610_nfc_ecc_mode(nfc, ECC_BYPASS);
break;

case NAND_CMD_ERASE1:
@@ -367,6 +435,9 @@ static void vf610_nfc_command(struct mtd_info *mtd, unsigned command,
}

vf610_nfc_done(nfc);
+
+ nfc->use_hw_ecc = false;
+ nfc->page_sz = 0;
}

static void vf610_nfc_read_buf(struct mtd_info *mtd, u_char *buf, int len)
@@ -392,6 +463,7 @@ static void vf610_nfc_write_buf(struct mtd_info *mtd, const uint8_t *buf,
l = min_t(uint, len, mtd->writesize + mtd->oobsize - c);
vf610_nfc_memcpy(nfc->regs + NFC_MAIN_AREA(0) + c, buf, l);

+ nfc->page_sz += l;
nfc->buf_offset += l;
}

@@ -459,6 +531,84 @@ static void vf610_nfc_select_chip(struct mtd_info *mtd, int chip)
#endif
}

+/* Count the number of 0's in buff up to max_bits */
+static inline int count_written_bits(uint8_t *buff, int size, int max_bits)
+{
+ uint32_t *buff32 = (uint32_t *)buff;
+ int k, written_bits = 0;
+
+ for (k = 0; k < (size / 4); k++) {
+ written_bits += hweight32(~buff32[k]);
+ if (written_bits > max_bits)
+ break;
+ }
+
+ return written_bits;
+}
+
+static inline int vf610_nfc_correct_data(struct mtd_info *mtd, uint8_t *dat)
+{
+ struct vf610_nfc *nfc = mtd_to_nfc(mtd);
+ u8 ecc_status;
+ u8 ecc_count;
+ int flip;
+
+ ecc_status = __raw_readb(nfc->regs + ECC_SRAM_ADDR * 8 + ECC_OFFSET);
+ ecc_count = ecc_status & ECC_ERR_COUNT;
+ if (!(ecc_status & ECC_STATUS_MASK))
+ return ecc_count;
+
+ /*
+ * On an erased page, bit count should be zero or at least
+ * less then half of the ECC strength
+ */
+ flip = count_written_bits(dat, nfc->chip.ecc.size, ecc_count);
+
+ if (flip > ecc_count && flip > (nfc->chip.ecc.strength / 2))
+ return -1;
+
+ /* Erased page. */
+ memset(dat, 0xff, nfc->chip.ecc.size);
+ return 0;
+}
+
+static int vf610_nfc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
+ uint8_t *buf, int oob_required, int page)
+{
+ int eccsize = chip->ecc.size;
+ int stat;
+
+ vf610_nfc_read_buf(mtd, buf, eccsize);
+
+ if (oob_required)
+ vf610_nfc_read_buf(mtd, chip->oob_poi, mtd->oobsize);
+
+ stat = vf610_nfc_correct_data(mtd, buf);
+
+ if (stat < 0)
+ mtd->ecc_stats.failed++;
+ else
+ mtd->ecc_stats.corrected += stat;
+
+ return 0;
+}
+
+static int vf610_nfc_write_page(struct mtd_info *mtd, struct nand_chip *chip,
+ const uint8_t *buf, int oob_required)
+{
+ struct vf610_nfc *nfc = mtd_to_nfc(mtd);
+
+ vf610_nfc_write_buf(mtd, buf, mtd->writesize);
+ if (oob_required)
+ vf610_nfc_write_buf(mtd, chip->oob_poi, mtd->oobsize);
+
+ /* Always write whole page including OOB due to HW ECC */
+ nfc->use_hw_ecc = true;
+ nfc->page_sz = mtd->writesize + mtd->oobsize;
+
+ return 0;
+}
+
static const struct of_device_id vf610_nfc_dt_ids[] = {
{ .compatible = "fsl,vf610-nfc" },
{ /* sentinel */ }
@@ -483,6 +633,16 @@ static int vf610_nfc_init_controller(struct vf610_nfc *nfc)
vf610_nfc_set_field(nfc, NFC_FLASH_CONFIG, CONFIG_PAGE_CNT_MASK,
CONFIG_PAGE_CNT_SHIFT, 1);

+ if (nfc->chip.ecc.mode == NAND_ECC_HW) {
+ /* Set ECC_STATUS offset */
+ vf610_nfc_set_field(nfc, NFC_FLASH_CONFIG,
+ CONFIG_ECC_SRAM_ADDR_MASK,
+ CONFIG_ECC_SRAM_ADDR_SHIFT, ECC_SRAM_ADDR);
+
+ /* Enable ECC_STATUS */
+ vf610_nfc_set(nfc, NFC_FLASH_CONFIG, CONFIG_ECC_SRAM_REQ_BIT);
+ }
+
return 0;
}

@@ -565,6 +725,45 @@ static int vf610_nfc_probe(struct platform_device *pdev)
goto error;
}

+ if (chip->ecc.mode == NAND_ECC_HW) {
+ if (mtd->writesize != PAGE_2K && mtd->oobsize < 64) {
+ dev_err(nfc->dev, "Unsupported flash with hwecc\n");
+ err = -ENXIO;
+ goto error;
+ }
+
+ if (chip->ecc.size != mtd->writesize) {
+ dev_err(nfc->dev, "Step size needs to be page size\n");
+ err = -ENXIO;
+ goto error;
+ }
+
+ /* Only 64 byte ECC layouts known */
+ if (mtd->oobsize > 64)
+ mtd->oobsize = 64;
+
+ if (chip->ecc.strength == 32) {
+ nfc->ecc_mode = ECC_60_BYTE;
+ chip->ecc.bytes = 60;
+ chip->ecc.layout = &vf610_nfc_ecc60;
+ } else if (chip->ecc.strength == 24) {
+ nfc->ecc_mode = ECC_45_BYTE;
+ chip->ecc.bytes = 45;
+ chip->ecc.layout = &vf610_nfc_ecc45;
+ } else {
+ dev_err(nfc->dev, "Unsupported ECC strength\n");
+ err = -ENXIO;
+ goto error;
+ }
+
+ /* propagate ecc.layout to mtd_info */
+ mtd->ecclayout = chip->ecc.layout;
+ chip->ecc.read_page = vf610_nfc_read_page;
+ chip->ecc.write_page = vf610_nfc_write_page;
+
+ chip->ecc.size = PAGE_2K;
+ }
+
/* second phase scan */
if (nand_scan_tail(mtd)) {
err = -ENXIO;
--
2.4.2