On 04/08/2018 09:04 AM, NeilBrown wrote:
> 
> 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 <n...@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 &&

I think this should be made winbond-specific, macronix flashes do not
suffer from this I think. Otherwise looks good.

> +                 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) */
> 


-- 
Best regards,
Marek Vasut

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