[PATCH v4 2/3] mtd: spi-nor: add support to unlock flash device.

[Sagar Shrikant Kadam <sagar.kadam@sifive.com>]

Nor device (is25wp256 mounted on HiFive unleashed Rev A00 board) from ISSI
have memory blocks guarded by block protection bits BP[0,1,2,3].

Clearing block protection bits,unlocks the flash memory regions
The unlock scheme is registered during nor scans.

Based on code developed by Wesley Terpstra <wesley@sifive.com>
and/or Palmer Dabbelt <palmer@sifive.com>.
https://github.com/riscv/riscv-linux/commit/c94e267766d62bc9a669611c3d0c8ed5ea26569b

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@sifive.com>
---
 drivers/mtd/spi-nor/spi-nor.c | 51 ++++++++++++++++++++++++++++++++++++++++++-
 include/linux/mtd/spi-nor.h   |  1 +
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index c5408ed..3942b26 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1461,6 +1461,49 @@ static int macronix_quad_enable(struct spi_nor *nor)
 }
 
 /**
+ * issi_unlock() - clear BP[0123] write-protection.
+ * @nor: pointer to a 'struct spi_nor'.
+ * @ofs: offset from which to unlock memory.
+ * @len: number of bytes to unlock.
+ *
+ * Bits [2345] of the Status Register are BP[0123].
+ * ISSI chips use a different block protection scheme than other chips.
+ * Just disable the write-protect unilaterally.
+ *
+ * Return: 0 on success, -errno otherwise.
+ */
+static int issi_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)
+{
+	int ret, val;
+	u8 mask = SR_BP0 | SR_BP1 | SR_BP2 | SR_BP3;
+
+	val = read_sr(nor);
+	if (val < 0)
+		return val;
+	if (!(val & mask))
+		return 0;
+
+	write_enable(nor);
+
+	write_sr(nor, val & ~mask);
+
+	ret = spi_nor_wait_till_ready(nor);
+	if (ret)
+		return ret;
+
+	ret = read_sr(nor);
+	if (ret > 0 && !(ret & mask)) {
+		dev_info(nor->dev,
+			"ISSI Block Protection Bits cleared SR=0x%x", ret);
+		ret = 0;
+	} else {
+		dev_err(nor->dev, "ISSI Block Protection Bits not cleared\n");
+		ret = -EINVAL;
+	}
+	return ret;
+}
+
+/**
  * spansion_quad_enable() - set QE bit in Configuraiton Register.
  * @nor:	pointer to a 'struct spi_nor'
  *
@@ -1836,7 +1879,7 @@ static int sr2_bit7_quad_enable(struct spi_nor *nor)
 			SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ) },
 	{ "is25wp256", INFO(0x9d7019, 0, 64 * 1024, 1024,
 			SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ |
-			SPI_NOR_4B_OPCODES)
+			SPI_NOR_4B_OPCODES | SPI_NOR_HAS_LOCK)
 	},
 
 	/* Macronix */
@@ -4078,6 +4121,12 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 		nor->flash_is_locked = stm_is_locked;
 	}
 
+	/* NOR protection support for ISSI chips */
+	if (JEDEC_MFR(info) == SNOR_MFR_ISSI ||
+	    info->flags & SPI_NOR_HAS_LOCK) {
+		nor->flash_unlock = issi_unlock;
+
+	}
 	if (nor->flash_lock && nor->flash_unlock && nor->flash_is_locked) {
 		mtd->_lock = spi_nor_lock;
 		mtd->_unlock = spi_nor_unlock;
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index ff13297..9a7d719 100644
--- a/include/linux/mtd/spi-nor.h
+++ b/include/linux/mtd/spi-nor.h
@@ -127,6 +127,7 @@
 #define SR_BP0			BIT(2)	/* Block protect 0 */
 #define SR_BP1			BIT(3)	/* Block protect 1 */
 #define SR_BP2			BIT(4)	/* Block protect 2 */
+#define SR_BP3			BIT(5)	/* Block protect 3 for ISSI device*/
 #define SR_TB			BIT(5)	/* Top/Bottom protect */
 #define SR_SRWD			BIT(7)	/* SR write protect */
 /* Spansion/Cypress specific status bits */
-- 
1.9.1


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