[PATCH 1/5] pxa3xx_nand: enable PXA3xx bad block management

[Haojian Zhuang]

On Sat, Sep 26, 2009 at 1:04 AM, Mok Keith <ek9852 at gmail.com> wrote:
> Hi,
>
> Any reason to limit the max slot to 40 (PXA_MAX_SLOT). It seems the
> bad block management scheme is not scalable and have a limitation of
> up to 256M bytes flash size only. (256M, 128kB per block = 2048 blocks
> = 40 bad blocks)

Each slot is one page. It's used to record the relocation information.
Each relocation
information is composed by two items. One is the bad block number, the other one
is relocated block number. Both of these two items cost 16 bits. For
the large block
flash, it can save 511 relocation information at most.

In the head of slot, a 16-bit magic number and 16-bit total number of
relocation items are
recorders.

When the slot is used, the next written will be moved to the next
slot. It's used to protect
relocation recorders. If one slot is broken, driver could load the previous one.

When all 40 slots are used, driver could erase the whole block and
write again. This feature
isn't enabled in the patch.
>
> Also for the calibration of the 2% bad block area, according to most
> NAND specifications (checked Samsung, Hynix, Micron), nand flash
> vendor guarantee no more than 20 bad block per 1024 blocks and this
> rule is apply linearly.
>
> Would it be better to use the following otherwise when nand size is
> greater than 256M the no of bad block entries is not matched to
> specification:
> instead of:
>> +    entries = (entries * 2) / 100;
>
> use:
> +    entries = (entries * 10) / 512;

Yes, this formula is better. I will use this. Maybe I can use this
formula whatever
the flash is beyond 256M or not.

>
> May I know what is the use of PXA_BEGIN_SLOT ?
I'm sorry that I removed usage of PXA_BEGIN_SLOT. But I didn't clear the macro
definition.
>
> Keith
>

Now the new patch is in below.