Re: [PATCH v2 1/3] nand: omap2: Add support for flash-based bad block table

[Roger Quadros <rogerq@ti.com>]

Ezequiel,

On 09/08/2014 02:27 PM, Ezequiel Garcia wrote:
> This commit adds a new platform-data boolean property that enables use
> of a flash-based bad block table. This can also be enabled by setting
> the 'nand-on-flash-bbt' devicetree property.

I'm not much aware of how on-flash-BBT works internally, but will it break things if
we keep on-flash-BBT "enabled" as the default option and add a DT property only to
explicitly disable the on-flash-BBT?

> 
> If the flash BBT is not enabled, the driver falls back to use OOB
> bad block markers only, as before. If the flash BBT is enabled the
> kernel will keep track of bad blocks using a BBT, in addition to
> the OOB markers.
> 
> As explained by Brian Norris the reasons for using a BBT are:
> 
> ""
> The primary reason would be that NAND datasheets specify it these days.
> A better argument is that nobody guarantees that you can write a
> bad block marker to a worn out block; you may just get program failures.
> 
> This has been acknowledged by several developers over the last several
> years.
> 
> Additionally, you get a boot-time performance improvement if you only
> have to read a few pages, instead of a page or two from every block on
> the flash.
> ""

cheers,
-roger

> 
> Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
> ---
>  arch/arm/mach-omap2/gpmc.c                   | 2 ++
>  drivers/mtd/nand/omap2.c                     | 6 +++++-
>  include/linux/platform_data/mtd-nand-omap2.h | 1 +
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-omap2/gpmc.c b/arch/arm/mach-omap2/gpmc.c
> index 2f97228..b55a225 100644
> --- a/arch/arm/mach-omap2/gpmc.c
> +++ b/arch/arm/mach-omap2/gpmc.c
> @@ -1440,6 +1440,8 @@ static int gpmc_probe_nand_child(struct platform_device *pdev,
>  				break;
>  			}
>  
> +	gpmc_nand_data->flash_bbt = of_get_nand_on_flash_bbt(child);
> +
>  	val = of_get_nand_bus_width(child);
>  	if (val == 16)
>  		gpmc_nand_data->devsize = NAND_BUSWIDTH_16;
> diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
> index 5967b38..e1a9b31 100644
> --- a/drivers/mtd/nand/omap2.c
> +++ b/drivers/mtd/nand/omap2.c
> @@ -1663,7 +1663,6 @@ static int omap_nand_probe(struct platform_device *pdev)
>  	mtd->owner		= THIS_MODULE;
>  	nand_chip		= &info->nand;
>  	nand_chip->ecc.priv	= NULL;
> -	nand_chip->options	|= NAND_SKIP_BBTSCAN;
>  
>  	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>  	nand_chip->IO_ADDR_R = devm_ioremap_resource(&pdev->dev, res);
> @@ -1692,6 +1691,11 @@ static int omap_nand_probe(struct platform_device *pdev)
>  		nand_chip->chip_delay = 50;
>  	}
>  
> +	if (pdata->flash_bbt)
> +		nand_chip->bbt_options |= NAND_BBT_USE_FLASH | NAND_BBT_NO_OOB;
> +	else
> +		nand_chip->options |= NAND_SKIP_BBTSCAN;
> +
>  	/* scan NAND device connected to chip controller */
>  	nand_chip->options |= pdata->devsize & NAND_BUSWIDTH_16;
>  	if (nand_scan_ident(mtd, 1, NULL)) {
> diff --git a/include/linux/platform_data/mtd-nand-omap2.h b/include/linux/platform_data/mtd-nand-omap2.h
> index 16ec262..090bbab 100644
> --- a/include/linux/platform_data/mtd-nand-omap2.h
> +++ b/include/linux/platform_data/mtd-nand-omap2.h
> @@ -71,6 +71,7 @@ struct omap_nand_platform_data {
>  	struct mtd_partition	*parts;
>  	int			nr_parts;
>  	bool			dev_ready;
> +	bool			flash_bbt;
>  	enum nand_io		xfer_type;
>  	int			devsize;
>  	enum omap_ecc           ecc_opt;
>