RE: [RFC] spi-nor: fix cross die reads on Micron multi-die devices

[Bean Huo 霍斌斌 (beanhuo)]

Hi, Adam
This is true, but this only exist in Micron 65nm spi nor N25Q.
For our 45nm spi nor MT25Q , MT25TL and MT25Q, does exist this question.
So I think, can you differentiate between these in your patch?

> From: Adam Somerville <adamsomerville@xxxxxxxxx>
> 
> So as far as I can see there is a bug in the spi-nor driver when issuing die
> boundary crossing reads on Micron multi-die devices.
> Micron N25Q512A, N25Q00AA and probably any other Micron multi-die
> devices do not support a single read request that crosses a die boundary.
> 
> The current behaviour is that the address on the device wraps back to the
> start of the first die, with any data returned beyond the boundary being from
> the start of the first die.
> 
> To reproduce run:
> (assuming mtd0 is at offset 0 and spans across die boundary)
> 
> mtd_debug read /dev/mtd0 0x1FFFFF0 32 bad
> 
> and compare to:
> 
> mtd_debug read /dev/mtd0 0x1FFFFF0 16 good1 mtd_debug read /dev/mtd0
> 0x2000000 16 good2
> 
> Instead we should split the read request in to 1 read per die.
> 
> Tested on Cyclone 5 SOC with cadence-qspi connected to Micron n25q512ax3
> 
> Signed-off-by: Adam Somerville <adamsomerville@xxxxxxxxx>
> ---
>  drivers/mtd/spi-nor/spi-nor.c |   21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index ed0c19c..68dc20e 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -903,10 +903,19 @@ static const struct flash_info
> *spi_nor_read_id(struct spi_nor *nor)
>  	return ERR_PTR(-ENODEV);
>  }
> 
> +/*
> + * Micron multi-die devices do not support cross die boundary
> + * reads. Split the read request in to 1 read per die  */ #define
> +MIN_READ_BOUNDARY 0x2000000
> +#define DIST_TO_BOUNDARY(x)	\
> +		(MIN_READ_BOUNDARY - ((u32)x & (MIN_READ_BOUNDARY - 1)))
> +
>  static int spi_nor_read(struct mtd_info *mtd, loff_t from, size_t len,
>  			size_t *retlen, u_char *buf)
>  {
>  	struct spi_nor *nor = mtd_to_spi_nor(mtd);
> +	size_t read_len;
>  	int ret;
> 
>  	dev_dbg(nor->dev, "from 0x%08x, len %zd\n", (u32)from, len); @@
> -915,7 +924,17 @@ static int spi_nor_read(struct mtd_info *mtd, loff_t from,
> size_t len,
>  	if (ret)
>  		return ret;
> 
> -	ret = nor->read(nor, from, len, retlen, buf);
> +	do {
> +		read_len = min(len, DIST_TO_BOUNDARY(from));
> +
> +		ret = nor->read(nor, from, read_len, retlen, buf);
> +		if (ret)
> +			break;
> +
> +		from += read_len;
> +		buf += read_len;
> +		len -= read_len;
> +	} while (len > 0);
> 
>  	spi_nor_unlock_and_unprep(nor, SPI_NOR_OPS_READ);
>  	return ret;
> --
> 1.7.9.5