[PATCH v4 1/2] mtd: spi-nor: sst: Fix write enable before AAI sequence

[Hendrik Donner]

Hello,

On 3/11/26 11:30, Sanjaikumar V S wrote:
> From: Sanjaikumar V S <sanjaikumar.vs at dicortech.com>
> 
> When writing to SST flash starting at an odd address, a single byte is
> first programmed using the byte program (BP) command. After this
> operation completes, the flash hardware automatically clears the Write
> Enable Latch (WEL) bit.
> 
> If an AAI (Auto Address Increment) word program sequence follows, it
> requires WEL to be set. Without re-enabling writes, the AAI sequence
> fails.
> 
> Add spi_nor_write_enable() after the odd-address byte program when more
> data needs to be written. Use a local boolean for clarity.
> 
> Fixes: b199489d37b2 ("mtd: spi-nor: add the framework for SPI NOR")
> Cc: stable at vger.kernel.org
> Signed-off-by: Sanjaikumar V S <sanjaikumar.vs at dicortech.com>
> ---
>   drivers/mtd/spi-nor/sst.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/sst.c b/drivers/mtd/spi-nor/sst.c
> index 175211fe6a5e..db02c14ba16f 100644
> --- a/drivers/mtd/spi-nor/sst.c
> +++ b/drivers/mtd/spi-nor/sst.c
> @@ -203,6 +203,8 @@ static int sst_nor_write(struct mtd_info *mtd, loff_t to, size_t len,
>   
>   	/* Start write from odd address. */
>   	if (to % 2) {
> +		bool needs_write_enable = (len > 1);
> +
>   		/* write one byte. */
>   		ret = sst_nor_write_data(nor, to, 1, buf);
>   		if (ret < 0)
> @@ -210,6 +212,17 @@ static int sst_nor_write(struct mtd_info *mtd, loff_t to, size_t len,
>   
>   		to++;
>   		actual++;
> +
> +		/*
> +		 * Byte program clears the write enable latch. If more
> +		 * data needs to be written using the AAI sequence,
> +		 * re-enable writes.
> +		 */
> +		if (needs_write_enable) {
> +			ret = spi_nor_write_enable(nor);
> +			if (ret)
> +				goto out;
> +		}
>   	}
>   
>   	/* Write out most of the data here. */

found a board with

   spi-nor spi0.0: sst25vf032b (4096 Kbytes)

for testing. Tests are on top of

   94645aa41bf9e (mtd/spi-nor/next)

This should be done according to the datasheet and fixes that only 1
byte is written on writes to a an odd address and following AAI writes
fail, resulting in something looking like this:

ffa9 ffff ffff ffff ffff ffff ffff ffff

when

24a9 91b3 7cb6 f01c 2994 c368 fdad d3a2

was supposed to be written.

Tested-by: Hendrik Donner <hd at os-cillation.de>
Reviewed-by: Hendrik Donner <hd at os-cillation.de>

Regards,
Hendrik