[PATCH] mtd: m25p80: Micron SPI uses Macronix-style 4-byte addressing

[Marek Vasut]

Dear Brian Norris,

> For SPI NOR flash that are larger than 128Mbit (16MiB), we need 4 bytes
> of address space to reach the entire flash; however, the original SPI
> flash protocol used only 3 bytes for the address. So far, the practice
> for handling this has been either to use new command opcodes that are
> defined to use 4 bytes for their address, or to use special
> mode-switching command to configure all traditionally-3-byte-address
> commands to take 4 bytes instead.
> 
> Macronix and Spansion developed two incompatible methods for
> entering/exiting "4-byte address mode." Micron flash uses the Macronix
> method (OPCODE_{EN4B,EX4B}), not the Spansion method.
> 
> This patch solves addressing issues on Micron n25q256a and provides the
> ability to support other future Micron SPI flash >16MiB.
> 
> Quoting a Micron representative:
> 
>   "Majority of our NOR that needs 4-byte addressing (256Mb or 32MB and
>    higher) enter and exit 4byte through B7h and E9h commands. The
>    N25Q256A7xxx and N25Q512A7xxx parts do not support 4-byte addressing
>    mode via B7h or E9h command."
> 
> They further clarified that those that don't support the enter/exit
> opcodes (B7h/E9h) are manufactured specifically to come up by default in
> 4-byte mode. We don't need to treat those parts any diffently, as they
> will discard the EN4B opcode as a no-op.
> 
> Signed-off-by: Brian Norris <computersforpeace at gmail.com>
> Cc: Vivien Didelot <vivien.didelot at savoirfairelinux.com>
> Cc: Marek Vasut <marex at denx.de>
> Cc: <stable at vger.kernel.org> # 3.10+
> ---
>  drivers/mtd/devices/m25p80.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> index b5190c4..a759c1f 100644
> --- a/drivers/mtd/devices/m25p80.c
> +++ b/drivers/mtd/devices/m25p80.c
> @@ -169,6 +169,7 @@ static inline int set_4byte(struct m25p *flash, u32
> jedec_id, int enable) {
>  	switch (JEDEC_MFR(jedec_id)) {
>  	case CFI_MFR_MACRONIX:
> +	case CFI_MFR_ST: /* Micron, actually */
>  	case 0xEF /* winbond */:
>  		flash->command[0] = enable ? OPCODE_EN4B : OPCODE_EX4B;
>  		return spi_write(flash->spi, flash->command, 1);

The situation with the 4b addressing is a horrible mess :(

Acked-by: Marek Vasut <marex at denx.de>

Best regards,
Marek Vasut