Messages in this thread | | | From | Jonas Gorski <> | Date | Wed, 2 Dec 2015 21:44:04 +0100 | Subject | Re: [PATCH] mtd: brcmnand: Workaround false ECC uncorrectable errors |
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On Wed, Dec 2, 2015 at 9:17 PM, Simon Arlott <simon@fire.lp0.eu> wrote: > On 01/12/15 10:41, Jonas Gorski wrote: >> On Sat, Nov 28, 2015 at 8:23 PM, Simon Arlott <simon@fire.lp0.eu> wrote: >>> + >>> + /* Go to start of buffer */ >>> + buf -= FC_WORDS; >>> + >>> + /* Erased if all data bytes are 0xFF */ >>> + buf_erased = memchr_inv(buf, 0xFF, FC_WORDS) == NULL; >>> + >>> + if (!buf_erased) >>> + goto out_free; >> >> We now have a function exactly for that use case in 4.4, >> nand_check_erased_buf [1], consider using that. This also has the >> benefit of treating bit flips as correctable as long as the ECC scheme >> is strong enough. > > I have no idea whether or not it's appropriate to specify > bitflips_threshold > 0 so it'd just be a more complex way to do > a memchr_inv() search for 0xFF.
The threshold would be the amount of bitflips the code can correct, so basically ecc.strength (at least that is my understanding).
> The code also has to check for the hamming code bytes being all 0x00, > because according to the comments [2], the controller also has > difficulty with the non-erased all-0xFFs scenario too.
According to brcmnand.c hamming can fix up to fifteen bitflips, but in the current code you would fail a hamming protected all-0xff-page for even a single bitflip in the data or in the ecc bytes, which means that all-0xff-pages wouldn't be protected at all.
Jonas
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