mtd: m25p80: Fix 4 byte addressing mode for Micron devices.

According to the datasheet for Micron n25q256a (N25Q256A13ESF40F) 4-byte
addressing mode should be entered as follows:

<quote>
To enter or exit the 4-byte address mode, the WRITE ENABLE command
must be executed to set the write enable latch bit to 1. (Note: The
WRITE ENABLE command must NOT be executed on the N25Q256A83ESF40x and
N25Q256A83E1240x devices.) S# must be driven LOW. The effect of the
command is immediate; after the command has been executed, the write
enable latch bit is cleared to 0.
</quote>

Micron's portable way to perform this for all types of Micron flash
is to first issue a write enable, then switch the addressing mode
followed by a write disable to avoid leaving the flash in a write-
able state.

Signed-off-by: Elie De Brauwer <eliedebrauwer@email.com>
[Brian: reworked a bit]
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
index 26b14f9fcac6d129c3a2bc5c7a9fa7baea234691..6bc9618af0942528d67e7846810adf7c2288b75a 100644 (file)
--- a/drivers/mtd/devices/m25p80.c
+++ b/drivers/mtd/devices/m25p80.c
@@ -168,12 +168,25 @@ static inline int write_disable(struct m25p *flash)
  */
 static inline int set_4byte(struct m25p *flash, u32 jedec_id, int enable)
 {
+       int status;
+       bool need_wren = false;
+
        switch (JEDEC_MFR(jedec_id)) {
-       case CFI_MFR_MACRONIX:
        case CFI_MFR_ST: /* Micron, actually */
+               /* Some Micron need WREN command; all will accept it */
+               need_wren = true;
+       case CFI_MFR_MACRONIX:
        case 0xEF /* winbond */:
+               if (need_wren)
+                       write_enable(flash);
+
                flash->command[0] = enable ? OPCODE_EN4B : OPCODE_EX4B;
-               return spi_write(flash->spi, flash->command, 1);
+               status = spi_write(flash->spi, flash->command, 1);
+
+               if (need_wren)
+                       write_disable(flash);
+
+               return status;
        default:
                /* Spansion style */
                flash->command[0] = OPCODE_BRWR;