[PATCHv4 5/5] mtd: gpmi: prevent creating a new BBT when blockmark swapping is disabled

[Brian Norris]

Hi Lothar,

On Thu, Jun 12, 2014 at 03:20:45PM +0200, Lothar Waßmann wrote:
> Without blockmark swapping, there is no use in creating a BBT from
> scratch, so use a BBT descriptor with NAND_BBT_CREATE unset in this
> case.

I'm curious: what is your plan if there is no BBT available on your
device, or if it ever gets corrupted? IIUC, nand_bbt will just assume
you have no bad blocks, and it will never write a bad block table to
flash. This also means no subsequent discoverable bad blocks can be
recorded across power cycles, I believe.

Maybe you don't want to specify your own nand_bbt_descr's at all, but
you just need to set:

	chip->bbt_options |= NAND_BBT_CREATE_EMPTY | NAND_BBT_NO_OOB;

(Note: there's a little bit of fuzziness about NAND_BBT_* flags, where
some are targeted for the nand_chip::bbt_options field, and others
belong in struct nand_bbt_descr::options.)

But if for some reason we need to keep this patch, a comment below:

> Signed-off-by: Lothar Waßmann <LW at KARO-electronics.de>
> ---
>  drivers/mtd/nand/gpmi-nand/gpmi-nand.c |   28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> index 37537b4..fc710d7 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> @@ -43,6 +43,29 @@ static struct nand_bbt_descr gpmi_bbt_descr = {
>  	.pattern	= scan_ff_pattern
>  };
>  
> +static uint8_t bbt_pattern[] = {'B', 'b', 't', '0' };
> +static uint8_t mirror_pattern[] = {'1', 't', 'b', 'B' };
> +
> +static struct nand_bbt_descr bbt_main_no_oob_descr = {
> +	.options = NAND_BBT_LASTBLOCK | NAND_BBT_WRITE |
> +	NAND_BBT_2BIT | NAND_BBT_VERSION | NAND_BBT_PERCHIP |
> +	NAND_BBT_NO_OOB,

Please indent the above two lines a bit, preferably matching the
indentation of NAND_BBT_LASTBLOCK. It should be clear that this is a
continuation of the '.options' initialization.

> +	.len = 4,
> +	.veroffs = 4,
> +	.maxblocks = NAND_BBT_SCAN_MAXBLOCKS,
> +	.pattern = bbt_pattern,
> +};
> +
> +static struct nand_bbt_descr bbt_mirror_no_oob_descr = {
> +	.options = NAND_BBT_LASTBLOCK | NAND_BBT_WRITE |
> +	NAND_BBT_2BIT | NAND_BBT_VERSION | NAND_BBT_PERCHIP |
> +	NAND_BBT_NO_OOB,

Same here.

> +	.len = 4,
> +	.veroffs = 4,
> +	.maxblocks = NAND_BBT_SCAN_MAXBLOCKS,
> +	.pattern = mirror_pattern,
> +};
> +
>  /*
>   * We may change the layout if we can get the ECC info from the datasheet,
>   * else we will use all the (page + OOB).
> @@ -1728,8 +1751,11 @@ static int gpmi_nand_init(struct gpmi_nand_data *this)
>  			chip->bbt_options |= NAND_BBT_NO_OOB_BBM;
>  
>  		if (of_property_read_bool(this->dev->of_node,
> -						"fsl,no-blockmark-swap"))
> +						"fsl,no-blockmark-swap")) {
>  			this->swap_block_mark = false;
> +			chip->bbt_td = &bbt_main_no_oob_descr;
> +			chip->bbt_md = &bbt_mirror_no_oob_descr;

My initial recommendation for this patch and the previous patch means
that you could just drop both patches and replace them with the
following:

			/* Comment here to explain why... */
			chip->bbt_options |= NAND_BBT_CREATE_EMPTY |
					     NAND_BBT_NO_OOB |
					     NAND_BBT_NO_OOB_BBM;
> +		}
>  	}
>  	dev_dbg(this->dev, "Blockmark swapping %sabled\n",
>  		this->swap_block_mark ? "en" : "dis");

Brian