[PATCHv3][ 1/2] mtd: nand: mxc_nand: Enforce a minimum mtd_info writesize default value.

[Brian Norris]

On Mon, Jan 06, 2014 at 05:02:36PM +0100, Denis Carikli wrote:
> The linux/mtd/mtd.h header has a comment in the
>   mtd_info struct definition that says that
>   having a writesize of 0 is illegal.
> 
> When nand_flash_detect_onfi is called (in the case
>   of an ONFI flash), it will call the function
>   pointed by read_buf in order to get some parameters
>   of the flash chip, including its writesize.

Note that (for fixing buswidth issues when using x16 vs. x8)
nand_flash_detect_onfi() no longer uses read_buf(). So this shouldn't
actually be an issue any more, I don't think. But we still might want to
set some value, due to the strange implementation of read_buf() in this
driver.

> Before decoding the writesize value that was retrived
>   with that read, the mxc_nand's mtd_info struct had
>   a writesize set to zero.
> 
> Cc: David Woodhouse <dwmw2 at infradead.org>
> Cc: linux-mtd at lists.infradead.org
> Cc: Sascha Hauer <s.hauer at pengutronix.de>
> Cc: Eric Bénard <eric at eukrea.com>
> Signed-off-by: Denis Carikli <denis at eukrea.com>
> ---
> ChangeLog v2->v3:
> New patch in this serie.
> ---
>  drivers/mtd/nand/mxc_nand.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/mtd/nand/mxc_nand.c b/drivers/mtd/nand/mxc_nand.c
> index 567a5e5..d4d8d66 100644
> --- a/drivers/mtd/nand/mxc_nand.c
> +++ b/drivers/mtd/nand/mxc_nand.c
> @@ -1415,6 +1415,9 @@ static int mxcnd_probe(struct platform_device *pdev)
>  	mtd->dev.parent = &pdev->dev;
>  	mtd->name = DRIVER_NAME;
>  
> +	/* Enforce a minimum writesize */
> +	mtd->writesize = 512;
> +

Is this "initial" writesize just needed for the bounds checking in
read_buf() (and write_buf())? Then wouldn't it make sense to match the
buffer size allocated initially? See:

	/* allocate a temporary buffer for the nand_scan_ident() */
	host->data_buf = devm_kzalloc(&pdev->dev, PAGE_SIZE, GFP_KERNEL);

Also, I don't think you actually need the bounds checks in
read_buf()/write_buf(), although I guess there's no real harm...

>  	/* 50 us command delay time */
>  	this->chip_delay = 5;
>  

Brian