[PATCH v3 1/3] nand: omap2: Add support for flash-based bad block table

[Ezequiel Garcia]

On 18 September 2014 06:59, Brian Norris <computersforpeace at gmail.com> wrote:
> On Thu, Sep 11, 2014 at 12:02:08PM -0300, 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.
>>
>> 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.
>> ""
>>
>> Signed-off-by: Ezequiel Garcia <ezequiel at vanguardiasur.com.ar>
>
> Pushed this one to l2-mtd.git. Thanks!
>
> But I do have one question below, and I have comments for patch 2.
>
>> ---
>>  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;
>
> Can you remind me: why do you use SKIP_BBTSCAN? Doesn't that mean you're
> skipping all boot-time scanning for bad blocks, and resorting to
> on-demand scanning (chip->block_bad()) every time you need to check for
> bad blocks?
>

Honestly, I have *no* idea, I just retained the previous flag, so to
keep the exact same behavior.

Roger, any ideas? If I have to guess, I'd say this is an attempt to
save some boot time.
-- 
Ezequiel García, VanguardiaSur
www.vanguardiasur.com.ar