[PATCH v3] mtd/nand: don't use {read,write}_buf for 8-bit transfers

[Brian Norris]

+ Pekon, Ezequiel

Can one of you see how this patch works with your BeagleBones w/ x16
NAND?

Also, do you think on of you could take a look at killing the
nand_chip.read_word() callback, as Artem was originally requesting with
this patch? It only has one user (for bad block checking in
nand_block_bad(), which is currently only used when there is no BBT at
all), and it looks like it could be replaced with a call to
read_buf(mtd, buf, 2).

Hi Uwe,

On Tue, Nov 26, 2013 at 10:15:15PM +0100, Uwe Kleine-König wrote:
> According to the Open NAND Flash Interface Specification (ONFI) Revision
> 3.1 "Parameters are always transferred on the lower 8-bits of the data
> bus." for the Get Features and Set Features commands.
> 
> So using read_buf and write_buf is wrong for 16-bit wide nand chips as
> they use I/O[15:0]. The Get Features command is easily fixed using 4
> times the read_byte callback. For Set Features implement a new
> overwritable callback "write_byte". Still I expect the default to work
> just fine for all controllers and making it overwriteable was just done
> for symmetry.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
> ---
>  drivers/mtd/nand/nand_base.c | 61 +++++++++++++++++++++++++++++++++++++++++---
>  include/linux/mtd/nand.h     |  3 +++
>  2 files changed, 60 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index bd39f7b..27d755b 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
...
> @@ -2706,7 +2751,7 @@ static int nand_block_markbad(struct mtd_info *mtd, loff_t ofs)
>  }
>  
>  /**
> - * nand_onfi_set_features- [REPLACEABLE] set features for ONFI nand
> + * nand_onfi_set_features - [REPLACEABLE] set features for ONFI nand

This change is unrelated. (Yes, the whitespace should be fixed, but
probably not in this patch.)

>   * @mtd: MTD device structure
>   * @chip: nand chip info structure
>   * @addr: feature address.
...
> @@ -2731,7 +2779,7 @@ static int nand_onfi_set_features(struct mtd_info *mtd, struct nand_chip *chip,
>  }
>  
>  /**
> - * nand_onfi_get_features- [REPLACEABLE] get features for ONFI nand
> + * nand_onfi_get_features - [REPLACEABLE] get features for ONFI nand

Ditto.

>   * @mtd: MTD device structure
>   * @chip: nand chip info structure
>   * @addr: feature address.
...
> @@ -2812,6 +2863,8 @@ static void nand_set_defaults(struct nand_chip *chip, int busw)
>  		chip->block_markbad = nand_default_block_markbad;
>  	if (!chip->write_buf || chip->write_buf == nand_write_buf)
>  		chip->write_buf = busw ? nand_write_buf16 : nand_write_buf;
> +	if (!chip->write_byte)

This check should be:

	if (!chip->write_byte || chip->write_byte == nand_write_byte)

in order to match the rest of the functions, so they can be reset if the
buswidth is detected to be x16, and we re-call nand_set_defaults()
(e.g., when using NAND_BUSWIDTH_AUTO). See the comment:

  /* If called twice, pointers that depend on busw may need to be reset */

I know it's kind of ugly, but that's what we have for now.

> +		chip->write_byte = busw ? nand_write_byte16 : nand_write_byte;
>  	if (!chip->read_buf || chip->read_buf == nand_read_buf)
>  		chip->read_buf = busw ? nand_read_buf16 : nand_read_buf;
>  	if (!chip->scan_bbt)

Brian