Messages in this thread | | | Date | Wed, 2 Dec 2015 12:54:15 -0800 | From | Brian Norris <> | Subject | Re: [PATCH] mtd: brcmnand: Workaround false ECC uncorrectable errors |
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Hi,
On Wed, Dec 02, 2015 at 09:44:04PM +0100, Jonas Gorski wrote: > 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
Hamming only protects 1 bitflip. The '15' is the value used by the controller to represent Hamming (i.e., there is no BCH-15).
> 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.
BTW, I think Kamal had code to handle protecting bitflips in erased pages code in the Broadcom STB Linux BSP. Perhaps he can port that to upstream with nand_check_erased_ecc_chunk()? IIUC, that would probably handle your case too, Simon, although it wouldn't be optimal for an all-0xff check (i.e., bitflip_threshold == 0).
If that's really an issue (i.e., we have an implementation + data), I'm sure we could add optimization to nand_check_erased_ecc_chunk() to support the bitflip_threshold == 0 case.
Brian
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