[PATCH v3] mtd: rawnand: Add support for Macronix NAND randomizer

[Mason Yang]

Macronix NANDs support randomizer operation for user data scrambled,
which can be enabled with a SET_FEATURE.

User data written to the NAND device without randomizer is still readable
after randomizer function enabled.
The penalty of randomizer are subpage accesses prohibited and more time
period is needed in program operation and entering deep power-down mode.
i.e., tPROG 300us to 340us(randomizer enabled)

For more high-reliability concern, if subpage write not available with
hardware ECC and then to enable randomizer is recommended by default.
Driver checks byte 167 of Vendor Blocks in ONFI parameter page table
to see if this high-reliability function is supported. By adding a new
specific DT property in children nodes to enable randomizer function.
i.e.,

	nand: nand-controller@unit-address {

		nand@0 {
			reg = <0>;
			mxic,enable-randomizer-otp;
		};
	};

--
changelog
v3:
To enable randomizer by specific DT property in children nodes,
mxic,enable-randomizer-otp;

v2:
To enable randomizer by checking chip options NAND_NO_SUBPAGE_WRITE

v1:
To enable randomizer by sys-fs

Signed-off-by: Mason Yang <masonccyang@xxxxxxxxxxx>
---
 drivers/mtd/nand/raw/nand_macronix.c | 64 ++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/drivers/mtd/nand/raw/nand_macronix.c b/drivers/mtd/nand/raw/nand_macronix.c
index 58511ae..d5df09a 100644
--- a/drivers/mtd/nand/raw/nand_macronix.c
+++ b/drivers/mtd/nand/raw/nand_macronix.c
@@ -11,6 +11,13 @@
 #define MACRONIX_READ_RETRY_BIT BIT(0)
 #define MACRONIX_NUM_READ_RETRY_MODES 6
 
+#define MACRONIX_RANDOMIZER_BIT BIT(1)
+#define ONFI_FEATURE_ADDR_MXIC_RANDOMIZER 0xB0
+#define MACRONIX_RANDOMIZER_ENPGM BIT(0)
+#define MACRONIX_RANDOMIZER_RANDEN BIT(1)
+#define MACRONIX_RANDOMIZER_RANDOPT BIT(2)
+#define MACRONIX_RANDOMIZER_MODE_EXIT ~MACRONIX_RANDOMIZER_ENPGM
+
 struct nand_onfi_vendor_macronix {
 	u8 reserved;
 	u8 reliability_func;
@@ -29,15 +36,72 @@ static int macronix_nand_setup_read_retry(struct nand_chip *chip, int mode)
 	return nand_set_features(chip, ONFI_FEATURE_ADDR_READ_RETRY, feature);
 }
 
+static void macronix_nand_randomizer_check_enable(struct nand_chip *chip)
+{
+	u8 feature[ONFI_SUBFEATURE_PARAM_LEN];
+	int ret;
+
+	ret = nand_get_features(chip, ONFI_FEATURE_ADDR_MXIC_RANDOMIZER,
+				feature);
+	if (feature[0]) {
+		pr_info("Macronix NAND randomizer enabled:0x%x\n", feature[0]);
+		return;
+	}
+
+	feature[0] = MACRONIX_RANDOMIZER_ENPGM | MACRONIX_RANDOMIZER_RANDEN |
+		     MACRONIX_RANDOMIZER_RANDOPT;
+	ret = nand_set_features(chip, ONFI_FEATURE_ADDR_MXIC_RANDOMIZER,
+				feature);
+	if (ret)
+		goto err;
+
+	feature[0] = 0x0;
+	ret = nand_prog_page_op(chip, 0, 0, feature, 1);
+	if (ret)
+		goto err;
+
+	ret = nand_get_features(chip, ONFI_FEATURE_ADDR_MXIC_RANDOMIZER,
+				feature);
+	if (ret)
+		goto err;
+
+	feature[0] &= MACRONIX_RANDOMIZER_MODE_EXIT;
+	ret = nand_set_features(chip, ONFI_FEATURE_ADDR_MXIC_RANDOMIZER,
+				feature);
+	if (ret)
+		goto err;
+
+	pr_info("Macronix NAND randomizer enable ok\n");
+	return;
+err:
+	pr_err("Macronix NAND randomizer enable failed\n");
+}
+
 static void macronix_nand_onfi_init(struct nand_chip *chip)
 {
 	struct nand_parameters *p = &chip->parameters;
 	struct nand_onfi_vendor_macronix *mxic;
+	struct device_node *dn = nand_get_flash_node(chip);
+	int rand_otp = 0;
 
 	if (!p->onfi)
 		return;
 
+	if (of_find_property(dn, "mxic,enable-randomizer-otp", NULL))
+		rand_otp = 1;
+
 	mxic = (struct nand_onfi_vendor_macronix *)p->onfi->vendor;
+	if (rand_otp && chip->options & NAND_NO_SUBPAGE_WRITE &&
+	    mxic->reliability_func & MACRONIX_RANDOMIZER_BIT) {
+		if (p->supports_set_get_features) {
+			bitmap_set(p->set_feature_list,
+				   ONFI_FEATURE_ADDR_MXIC_RANDOMIZER, 1);
+			bitmap_set(p->get_feature_list,
+				   ONFI_FEATURE_ADDR_MXIC_RANDOMIZER, 1);
+			macronix_nand_randomizer_check_enable(chip);
+		}
+	}
+
 	if ((mxic->reliability_func & MACRONIX_READ_RETRY_BIT) == 0)
 		return;
 
-- 
1.9.1