[PATCH v2 1/2] spi-nor: add support for ISSI's block unlocking scheme

[Palmer Dabbelt <palmer@sifive.com>]

From: "Wesley W. Terpstra" <wesley@sifive.com>

ISSI uses a non-standard scheme to control block protection, with bit 5
of the status registerr controlling an additional block protection bit.
This patch disables all the block protection bits whenever an ISSI chip
is seen.

We might also want to trigger an error when writing SR_TB to these
chips, as it aliases with this extra protection bit in the status
register.  It looks like that's always conditional on SNOR_F_HAS_SR_TB,
so at least what's there is safe.

Signed-off-by: Wesley W. Terpstra <wesley@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
---
 drivers/mtd/spi-nor/spi-nor.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
 include/linux/mtd/spi-nor.h   |  2 ++
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index d9c368c44194..aab93463a5e7 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1515,6 +1515,44 @@ static int macronix_quad_enable(struct spi_nor *nor)
 	return 0;
 }
 
+/**
+ * issi_unlock() - clear BP[0123] write-protection.
+ * @nor:	pointer to a 'struct spi_nor'
+ *
+ * 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)
+{
+	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)) {
+		return 0;
+	} else {
+		dev_err(nor->dev, "ISSI Block Protection Bits not cleared\n");
+		return -EINVAL;
+	}
+}
+
 /*
  * Write status Register and configuration register with 2 bytes
  * The first byte will be written to the status register, while the
@@ -2747,6 +2785,9 @@ static int spi_nor_init(struct spi_nor *nor)
 		spi_nor_wait_till_ready(nor);
 	}
 
+	if (JEDEC_MFR(nor->info) == SNOR_MFR_ISSI)
+		issi_unlock(nor);
+
 	if (nor->quad_enable) {
 		err = nor->quad_enable(nor);
 		if (err) {
@@ -2926,7 +2967,7 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 	if (ret)
 		return ret;
 
-	if (nor->addr_width) {
+	if (nor->addr_width && JEDEC_MFR(info) != SNOR_MFR_ISSI) {
 		/* already configured from SFDP */
 	} else if (info->addr_width) {
 		nor->addr_width = info->addr_width;
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index e60da0d34cc1..da422a37d383 100644
--- a/include/linux/mtd/spi-nor.h
+++ b/include/linux/mtd/spi-nor.h
@@ -23,6 +23,7 @@
 #define SNOR_MFR_ATMEL		CFI_MFR_ATMEL
 #define SNOR_MFR_GIGADEVICE	0xc8
 #define SNOR_MFR_INTEL		CFI_MFR_INTEL
+#define SNOR_MFR_ISSI		0x9d
 #define SNOR_MFR_MICRON		CFI_MFR_ST /* ST Micro <--> Micron */
 #define SNOR_MFR_MACRONIX	CFI_MFR_MACRONIX
 #define SNOR_MFR_SPANSION	CFI_MFR_AMD
@@ -121,6 +122,7 @@
 #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 (on ISSI chips) */
 #define SR_TB			BIT(5)	/* Top/Bottom protect */
 #define SR_SRWD			BIT(7)	/* SR write protect */
 /* Spansion/Cypress specific status bits */
-- 
2.16.4