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SubjectRe: [PATCH v4] mtd: spi-nor: clear Winbond Extended Address Reg on switch to 3-byte addressing.
On Sat, 21 Apr 2018 08:54:40 +1000
NeilBrown <neil@brown.name> wrote:

> Winbond spi-nor flash 32MB and larger have an 'Extended Address
> Register' as one option for addressing beyond 16MB (Macronix
> has the same concept, Spansion has EXTADD bits in the Bank Address
> Register).
>
> 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.
>
> So the documentation suggests clearing the EAR after switching to
> 3-byte mode. Experimentation shows that the EAR is *always* one after
> the switch to 3-byte mode, so clearing the EAR is mandatory at
> shutdown for a subsequent 3-byte-addressed reboot to work.
>
> Note that some SOCs (e.g. MT7621) do not assert a reset line at normal
> reboot, so we cannot rely on hardware reset. The MT7621 does assert a
> reset line at watchdog-reset.
>
> Acked-by: Marek Vasut <marek.vasut@gmail.com>
> Signed-off-by: NeilBrown <neil@brown.name>

Applied to spi-nor/next.

Thanks,

Boris

> ---
>
> Changes since v3:
> Removed Fixes/stable tags. Added Acked-by from Marek.
> Changes sinc3 v2:
> Fixed comment style.
>
>
> drivers/mtd/spi-nor/spi-nor.c | 14 ++++++++++++++
> include/linux/mtd/spi-nor.h | 2 ++
> 2 files changed, 16 insertions(+)
>
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 5bfa36e95f35..42ae9a1529bb 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -284,6 +284,20 @@ static inline int set_4byte(struct spi_nor *nor, const struct flash_info *info,
> if (need_wren)
> write_disable(nor);
>
> + if (!status && !enable &&
> + JEDEC_MFR(info) == SNOR_MFR_WINBOND) {
> + /*
> + * On Winbond W25Q256FV, leaving 4byte mode causes
> + * the Extended Address Register to be set to 1, so all
> + * 3-byte-address reads come from the second 16M.
> + * We must clear the register to enable normal behavior.
> + */
> + write_enable(nor);
> + nor->cmd_buf[0] = 0;
> + nor->write_reg(nor, SPINOR_OP_WREAR, nor->cmd_buf, 1);
> + write_disable(nor);
> + }
> +
> return status;
> default:
> /* Spansion style */
> diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
> index de36969eb359..e60da0d34cc1 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_RDEAR 0xc8 /* Read Extended Address Register */
> +#define SPINOR_OP_WREAR 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) */

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