RE: [RFC] spi-nor: fix cross die reads on Micron multi-die devices
From: Bean Huo 霍斌斌 (beanhuo)
Date: Tue Jan 19 2016 - 21:47:32 EST
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