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Subject[PATCH] mtd: spi-nor: clear Extended Address Reg on switch to 3-byte addressing.

According to section
8.2.7 Write Extended Address Register (C5h)

of the Winbond W25Q256FV data sheet (256M-BIT SPI flash)

The Extended Address Register is only effective when the device is
in the 3-Byte Address Mode. When the device operates in the 4-Byte
Address Mode (ADS=1), any command with address input of A31-A24
will replace the Extended Address Register values. It is
recommended to check and update the Extended Address Register if
necessary when the device is switched from 4-Byte to 3-Byte Address
Mode.

This patch adds code to implement that recommendation. Without this,
my GNUBEE-PC1 will not successfully reboot, as the Extended Address
Register is left with a value of '1'. When the SOC attempts to read
(in 3-byte address mode) the boot loader, it reads from the wrong
location.

Signed-off-by: NeilBrown <neil@brown.name>
---
drivers/mtd/spi-nor/spi-nor.c | 10 ++++++++++
include/linux/mtd/spi-nor.h | 2 ++
2 files changed, 12 insertions(+)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index d445a4d3b770..c303bf0d2982 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -269,6 +269,7 @@ static inline int set_4byte(struct spi_nor *nor, const struct flash_info *info,
int status;
bool need_wren = false;
u8 cmd;
+ u8 val;

switch (JEDEC_MFR(info)) {
case SNOR_MFR_MICRON:
@@ -283,6 +284,15 @@ static inline int set_4byte(struct spi_nor *nor, const struct flash_info *info,
status = nor->write_reg(nor, cmd, NULL, 0);
if (need_wren)
write_disable(nor);
+ if (!status && !enable &&
+ nor->read_reg(nor, SPINOR_OP_RDXA, &val, 1) == 0 &&
+ val != 0) {
+ /* need to reset the Extended Address Register */
+ write_enable(nor);
+ val = 0;
+ nor->write_reg(nor, SPINOR_OP_WRXA, &val, 1);
+ write_disable(nor);
+ }

return status;
default:
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index de36969eb359..42954419cfdf 100644
--- a/include/linux/mtd/spi-nor.h
+++ b/include/linux/mtd/spi-nor.h
@@ -62,6 +62,8 @@
#define SPINOR_OP_RDCR 0x35 /* Read configuration register */
#define SPINOR_OP_RDFSR 0x70 /* Read flag status register */
#define SPINOR_OP_CLFSR 0x50 /* Clear flag status register */
+#define SPINOR_OP_RDXA 0xc8 /* Read Extended Address Register */
+#define SPINOR_OP_WRXA 0xc5 /* Write Extended Address Register */

/* 4-byte address opcodes - used on Spansion and some Macronix flashes. */
#define SPINOR_OP_READ_4B 0x13 /* Read data bytes (low frequency) */
--
2.14.0.rc0.dirty
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