[PATCH v6 2/3] mtd: spi-nor: add support to unlock flash device

[Sagar Shrikant Kadam]

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].
Add identifier within flash info structure to indicate that a particular
flash device has the fourth block protect bit (SPI_NOR_HAS_BP3).
Increase size of flash_info flags from u16 to u32 to accommodate
SPI_NOR_HAS_BP3.

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@xxxxxxxxxx>
and/or Palmer Dabbelt <palmer@xxxxxxxxxx>.
https://github.com/riscv/riscv-linux/commit/c94e267766d62bc9a669611c3d0c8ed5ea26569b

spell correction: "Configuration" in spansion_quad_enable function
description.

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@xxxxxxxxxx>
---
 drivers/mtd/spi-nor/spi-nor.c | 66 ++++++++++++++++++++++++++++++++++++++++---
 include/linux/mtd/spi-nor.h   |  1 +
 2 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index c816f0c..d165fcd 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -250,7 +250,7 @@ struct flash_info {
 	u16		page_size;
 	u16		addr_width;
 
-	u16		flags;
+	u32		flags;
 #define SECT_4K			BIT(0)	/* SPINOR_OP_BE_4K works uniformly */
 #define SPI_NOR_NO_ERASE	BIT(1)	/* No erase command needed */
 #define SST_WRITE		BIT(2)	/* use SST byte programming */
@@ -279,6 +279,13 @@ struct flash_info {
 #define SPI_NOR_SKIP_SFDP	BIT(13)	/* Skip parsing of SFDP tables */
 #define USE_CLSR		BIT(14)	/* use CLSR command */
 #define SPI_NOR_OCTAL_READ	BIT(15)	/* Flash supports Octal Read */
+#define SPI_NOR_HAS_BP3		BIT(16)	/*
+					 * Flash SR has block protect bits
+					 * for lock/unlock purpose, few support
+					 * BP0-BP2 while few support BP0-BP3.
+					 * This flag identifies devices that
+					 * support BP3 bit.
+					 */
 
 	/* Part specific fixup hooks. */
 	const struct spi_nor_fixups *fixups;
@@ -1461,7 +1468,50 @@ static int macronix_quad_enable(struct spi_nor *nor)
 }
 
 /**
- * spansion_quad_enable() - set QE bit in Configuraiton Register.
+ * 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 protect bits cleared SR: 0x%x\n",
+			 ret);
+		ret = 0;
+	} else {
+		dev_err(nor->dev, "ISSI block protect bits not cleared\n");
+		ret = -EINVAL;
+	}
+	return ret;
+}
+
+/**
+ * spansion_quad_enable() - set QE bit in Configuration Register.
  * @nor:	pointer to a 'struct spi_nor'
  *
  * Set the Quad Enable (QE) bit in the Configuration Register.
@@ -1834,9 +1884,10 @@ static int sr2_bit7_quad_enable(struct spi_nor *nor)
 			SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ) },
 	{ "is25wp128",  INFO(0x9d7018, 0, 64 * 1024, 256,
 			SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ) },
-	{ "is25wp256", INFO(0x9d7019, 0, 64 * 1024, 1024,
+	{ "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 | SPI_NOR_HAS_TB |
+			SPI_NOR_HAS_BP3)
 	},
 
 	/* Macronix */
@@ -4080,6 +4131,13 @@ 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 &&
+	    info->flags & SPI_NOR_HAS_BP3) {
+		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..256a8b6 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 */
 #define SR_TB			BIT(5)	/* Top/Bottom protect */
 #define SR_SRWD			BIT(7)	/* SR write protect */
 /* Spansion/Cypress specific status bits */
-- 
1.9.1