HW-ECC and erase detect [was: PATCH V2 fix mtd: gpmi: fix the bitflips for erased page]

[Huang Shijie]

On Fri, Jan 10, 2014 at 03:46:20PM -0500, Bill Pringlemeir wrote:
> I think 'fsmc_nand' will not detect the 'all ff data' and ECC failed
> condition?  Also, it seems that UBI will write mostly xFF pages when
> just an EC page/sub-page is marked, so these type of pages maybe fairly
> common in practice.
> 
> It certainly would be a nice feature for a hardware ECC which writes to
> the OOB data to have an 'erase detect' bit in the ECC status.  I looked
> at some other MTD devices and it didn't seem they had to handle this.
> Do some controller recognize an erased page and give an ECC status as
> ok?
In fact, the gpmi can supports this feature by set the HW_BCH_MODE:ERASE_THRESHOLD.
but Elie had proved it is a IC bug.

I have issued a request to the hardware guy, and hope they can fix it in the
future.

thanks
Huang Shijie