Hi Boris,
2017-03-31 1:30 GMT+09:00 Boris Brezillon <boris.brezil...@free-electrons.com>: > On Thu, 30 Mar 2017 17:15:03 +0900 > Masahiro Yamada <yamada.masah...@socionext.com> wrote: > >> Recent versions of this IP support automatic erased page detection. >> If an erased page is detected on reads, the controller does not set >> INTR__ECC_UNCOR_ERR, but INTR__ERASED_PAGE. If this feature is >> supported, the driver can use this information instead of calling >> nand_check_erased_ecc_chunk(). >> >> The detection of erased page is based on the number of zeros in the >> page; if the number of zeros is less than the value in the field >> ERASED_THRESHOLD, the page is assumed as erased. >> >> Set the ERASED_THRESHOLD to (chip->ecc.strength + 1). This is the >> worst case where all the bitflips come from the same ECC sector. >> This field is Reserved for older IP versions, so this commit has >> no impact on them. > > Do you have a way to know the actual number of bitflips in an erased > ECC block? There is no way to the actual number of bitflips except that the driver parses the whole buffer counting bitflips. > BTW, is the threshold a per-page information or a per ECC > block information. Per-page. Honestly, this hardware feature is not nice because per-chunk threshold makes sense . > If you can't know the real number of bitflips I don't think it's safe > to set the threshold to chip->ecc.strength + 1. Right. > You can still use the feature to detect erased pages without any > bitflips (set ERASED_THRESHOLD to 1), which should be the case most of > the time, but for cases where you have bitflips I'd recommend using > nand_check_erased_ecc_chunk() if you can't know the actual number of > bitflips in the page. > You are right. Probably, this feature can work safely only when ERASED_THRESHOLD == 1. I decided to drop this patch from v4 for now, but I will consider it. -- Best Regards Masahiro Yamada
