mtd: nand: add support for Micron on-die ECC

Now that the core NAND subsystem has support for on-die ECC, this commit
brings the necessary code to support on-die ECC on Micron NANDs.

In micron_nand_init(), we detect if the Micron NAND chip supports on-die
ECC mode, by checking a number of conditions:

 - It must be an ONFI NAND
 - It must be a SLC NAND

 - Enabling *and* disabling on-die ECC must work

 - The on-die ECC must be correcting 4 bits per 512 bytes of data. Some
   Micron NAND chips have an on-die ECC able to correct 8 bits per 512
   bytes of data, but they work slightly differently and therefore we
   don't support them in this patch.

Then, if the on-die ECC cannot be disabled (some Micron NAND have on-die
ECC forcefully enabled), we bail out, as we don't support such
NANDs. Indeed, the implementation of raw_read()/raw_write() make the
assumption that on-die ECC can be disabled. Support for Micron NANDs
with on-die ECC forcefully enabled can easily be added, but in the
absence of such HW for testing, we preferred to simply bail out.

If the on-die ECC is supported, and requested in the Device Tree, then
it is indeed enabled, by using custom implementations of the
->read_page(), ->read_page_raw(), ->write_page() and ->write_page_raw()
operation to properly handle the on-die ECC.

In the non-raw functions, we need to enable the internal ECC engine
before issuing the NAND_CMD_READ0 or NAND_CMD_SEQIN commands, which is
why we set the NAND_ECC_CUSTOM_PAGE_ACCESS option at initialization
time (it asks the NAND core to let the NAND driver issue those
commands).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

diff --git a/drivers/mtd/nand/nand_micron.c b/drivers/mtd/nand/nand_micron.c
index 8770110692519636caca8d501388a74d70642739..9993f8ead1e2f4ab26d41e21416befd3054d8d89 100644 (file)
--- a/drivers/mtd/nand/nand_micron.c
+++ b/drivers/mtd/nand/nand_micron.c
@@ -17,6 +17,12 @@
 
 #include <linux/mtd/nand.h>
 
+/*
+ * Special Micron status bit that indicates when the block has been
+ * corrected by on-die ECC and should be rewritten
+ */
+#define NAND_STATUS_WRITE_RECOMMENDED  BIT(3)
+
 struct nand_onfi_vendor_micron {
        u8 two_plane_read;
        u8 read_cache;
@@ -66,9 +72,191 @@ static int micron_nand_onfi_init(struct nand_chip *chip)
        return 0;
 }
 
+static int micron_nand_on_die_ooblayout_ecc(struct mtd_info *mtd, int section,
+                                           struct mtd_oob_region *oobregion)
+{
+       if (section >= 4)
+               return -ERANGE;
+
+       oobregion->offset = (section * 16) + 8;
+       oobregion->length = 8;
+
+       return 0;
+}
+
+static int micron_nand_on_die_ooblayout_free(struct mtd_info *mtd, int section,
+                                            struct mtd_oob_region *oobregion)
+{
+       if (section >= 4)
+               return -ERANGE;
+
+       oobregion->offset = (section * 16) + 2;
+       oobregion->length = 6;
+
+       return 0;
+}
+
+static const struct mtd_ooblayout_ops micron_nand_on_die_ooblayout_ops = {
+       .ecc = micron_nand_on_die_ooblayout_ecc,
+       .free = micron_nand_on_die_ooblayout_free,
+};
+
+static int micron_nand_on_die_ecc_setup(struct nand_chip *chip, bool enable)
+{
+       u8 feature[ONFI_SUBFEATURE_PARAM_LEN] = { 0, };
+
+       if (enable)
+               feature[0] |= ONFI_FEATURE_ON_DIE_ECC_EN;
+
+       return chip->onfi_set_features(nand_to_mtd(chip), chip,
+                                      ONFI_FEATURE_ON_DIE_ECC, feature);
+}
+
+static int
+micron_nand_read_page_on_die_ecc(struct mtd_info *mtd, struct nand_chip *chip,
+                                uint8_t *buf, int oob_required,
+                                int page)
+{
+       int status;
+       int max_bitflips = 0;
+
+       micron_nand_on_die_ecc_setup(chip, true);
+
+       chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
+       chip->cmdfunc(mtd, NAND_CMD_STATUS, -1, -1);
+       status = chip->read_byte(mtd);
+       if (status & NAND_STATUS_FAIL)
+               mtd->ecc_stats.failed++;
+       /*
+        * The internal ECC doesn't tell us the number of bitflips
+        * that have been corrected, but tells us if it recommends to
+        * rewrite the block. If it's the case, then we pretend we had
+        * a number of bitflips equal to the ECC strength, which will
+        * hint the NAND core to rewrite the block.
+        */
+       else if (status & NAND_STATUS_WRITE_RECOMMENDED)
+               max_bitflips = chip->ecc.strength;
+
+       chip->cmdfunc(mtd, NAND_CMD_READ0, -1, -1);
+
+       nand_read_page_raw(mtd, chip, buf, oob_required, page);
+
+       micron_nand_on_die_ecc_setup(chip, false);
+
+       return max_bitflips;
+}
+
+static int
+micron_nand_write_page_on_die_ecc(struct mtd_info *mtd, struct nand_chip *chip,
+                                 const uint8_t *buf, int oob_required,
+                                 int page)
+{
+       micron_nand_on_die_ecc_setup(chip, true);
+
+       chip->cmdfunc(mtd, NAND_CMD_SEQIN, 0x00, page);
+       nand_write_page_raw(mtd, chip, buf, oob_required, page);
+       chip->cmdfunc(mtd, NAND_CMD_PAGEPROG, -1, -1);
+
+       micron_nand_on_die_ecc_setup(chip, false);
+
+       return 0;
+}
+
+static int
+micron_nand_read_page_raw_on_die_ecc(struct mtd_info *mtd,
+                                    struct nand_chip *chip,
+                                    uint8_t *buf, int oob_required,
+                                    int page)
+{
+       chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
+       nand_read_page_raw(mtd, chip, buf, oob_required, page);
+
+       return 0;
+}
+
+static int
+micron_nand_write_page_raw_on_die_ecc(struct mtd_info *mtd,
+                                     struct nand_chip *chip,
+                                     const uint8_t *buf, int oob_required,
+                                     int page)
+{
+       chip->cmdfunc(mtd, NAND_CMD_SEQIN, 0x00, page);
+       nand_write_page_raw(mtd, chip, buf, oob_required, page);
+       chip->cmdfunc(mtd, NAND_CMD_PAGEPROG, -1, -1);
+
+       return 0;
+}
+
+enum {
+       /* The NAND flash doesn't support on-die ECC */
+       MICRON_ON_DIE_UNSUPPORTED,
+
+       /*
+        * The NAND flash supports on-die ECC and it can be
+        * enabled/disabled by a set features command.
+        */
+       MICRON_ON_DIE_SUPPORTED,
+
+       /*
+        * The NAND flash supports on-die ECC, and it cannot be
+        * disabled.
+        */
+       MICRON_ON_DIE_MANDATORY,
+};
+
+/*
+ * Try to detect if the NAND support on-die ECC. To do this, we enable
+ * the feature, and read back if it has been enabled as expected. We
+ * also check if it can be disabled, because some Micron NANDs do not
+ * allow disabling the on-die ECC and we don't support such NANDs for
+ * now.
+ *
+ * This function also has the side effect of disabling on-die ECC if
+ * it had been left enabled by the firmware/bootloader.
+ */
+static int micron_supports_on_die_ecc(struct nand_chip *chip)
+{
+       u8 feature[ONFI_SUBFEATURE_PARAM_LEN] = { 0, };
+       int ret;
+
+       if (chip->onfi_version == 0)
+               return MICRON_ON_DIE_UNSUPPORTED;
+
+       if (chip->bits_per_cell != 1)
+               return MICRON_ON_DIE_UNSUPPORTED;
+
+       ret = micron_nand_on_die_ecc_setup(chip, true);
+       if (ret)
+               return MICRON_ON_DIE_UNSUPPORTED;
+
+       chip->onfi_get_features(nand_to_mtd(chip), chip,
+                               ONFI_FEATURE_ON_DIE_ECC, feature);
+       if ((feature[0] & ONFI_FEATURE_ON_DIE_ECC_EN) == 0)
+               return MICRON_ON_DIE_UNSUPPORTED;
+
+       ret = micron_nand_on_die_ecc_setup(chip, false);
+       if (ret)
+               return MICRON_ON_DIE_UNSUPPORTED;
+
+       chip->onfi_get_features(nand_to_mtd(chip), chip,
+                               ONFI_FEATURE_ON_DIE_ECC, feature);
+       if (feature[0] & ONFI_FEATURE_ON_DIE_ECC_EN)
+               return MICRON_ON_DIE_MANDATORY;
+
+       /*
+        * Some Micron NANDs have an on-die ECC of 4/512, some other
+        * 8/512. We only support the former.
+        */
+       if (chip->onfi_params.ecc_bits != 4)
+               return MICRON_ON_DIE_UNSUPPORTED;
+
+       return MICRON_ON_DIE_SUPPORTED;
+}
+
 static int micron_nand_init(struct nand_chip *chip)
 {
        struct mtd_info *mtd = nand_to_mtd(chip);
+       int ondie;
        int ret;
 
        ret = micron_nand_onfi_init(chip);
@@ -78,6 +266,34 @@ static int micron_nand_init(struct nand_chip *chip)
        if (mtd->writesize == 2048)
                chip->bbt_options |= NAND_BBT_SCAN2NDPAGE;
 
+       ondie = micron_supports_on_die_ecc(chip);
+
+       if (ondie == MICRON_ON_DIE_MANDATORY) {
+               pr_err("On-die ECC forcefully enabled, not supported\n");
+               return -EINVAL;
+       }
+
+       if (chip->ecc.mode == NAND_ECC_ON_DIE) {
+               if (ondie == MICRON_ON_DIE_UNSUPPORTED) {
+                       pr_err("On-die ECC selected but not supported\n");
+                       return -EINVAL;
+               }
+
+               chip->ecc.options = NAND_ECC_CUSTOM_PAGE_ACCESS;
+               chip->ecc.bytes = 8;
+               chip->ecc.size = 512;
+               chip->ecc.strength = 4;
+               chip->ecc.algo = NAND_ECC_BCH;
+               chip->ecc.read_page = micron_nand_read_page_on_die_ecc;
+               chip->ecc.write_page = micron_nand_write_page_on_die_ecc;
+               chip->ecc.read_page_raw =
+                       micron_nand_read_page_raw_on_die_ecc;
+               chip->ecc.write_page_raw =
+                       micron_nand_write_page_raw_on_die_ecc;
+
+               mtd_set_ooblayout(mtd, &micron_nand_on_die_ooblayout_ops);
+       }
+
        return 0;
 }
 

diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 28f7dd9177e924ada131e4ad8ec1224fae3920f9..893d0ce08030dbe30457a808fba4262a3d0eba9b 100644 (file)
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -258,6 +258,8 @@ struct nand_chip;
 
 /* Vendor-specific feature address (Micron) */
 #define ONFI_FEATURE_ADDR_READ_RETRY   0x89
+#define ONFI_FEATURE_ON_DIE_ECC                0x90
+#define   ONFI_FEATURE_ON_DIE_ECC_EN   BIT(3)
 
 /* ONFI subfeature parameters length */
 #define ONFI_SUBFEATURE_PARAM_LEN      4