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SubjectRe: fsl_ifc_nand: are blank pages protected by ECC?
On Wed, 19 Apr 2017 14:13:32 +0200
Pavel Machek <pavel@ucw.cz> wrote:

> Hi!
>
> We have some problems with fsl_ifc_nand ... in the old kernels, but
> this one does not seem to be fixed in v4.11, either.
>
> UBIFS complains:
>
> UBIFS error (pid 931): ubifs_scan: corrupt empty space at LEB 282:252630
> UBIFS error (pid 931): ubifs_scanned_corruption: corruption at LEB 282:252630
> UBIFS error (pid 931): ubifs_scanned_corruption: first 1322 bytes from LEB 282:252630
> UBIFS error (pid 931): ubifs_scan: LEB 282 scanning failed
>
> Possible explanation is here:
>
> https://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/t/289605
>
> # I see on the forum that this issue has been raised before - my
> # understanding is that the omap2 nand driver does not perform ECC
> # detection/correction on empty pages so when UBIFS checks the empty
> # space data and doesn't read all 0xFF then it fails and mounts
> # read-only. I didn't find any good solution - only a workaround to
> # remove the UBIFS check..
>
> So I checked fsl_ifc_nand.c in v4.11-rc, and yes, it seems to have the
> same problem:
>
> if (errors == 15) {
> /*
> * Uncorrectable error.
> * OK only if the whole page is blank.
> *
> * We disable ECCER reporting due to...
> * erratum IFC-A002770 -- so report it now if we
> * see an uncorrectable error in ECCSTAT.
> */
> if (!is_blank(mtd, bufnum))
> ctrl->nand_stat |=
> IFC_NAND_EVTER_STAT_ECCER;
> break;
> }
>
> is_blank() checks for all 0xff's, so single-bit 0xfe in the data will
> result in_blank() == 0 and uncorrectable error being signaled.
>
> Should the driver be modified somehow?

Yep, nand_check_erased_ecc_chunk() [1] is here to help you check this
case, unfortunately, it's not directly applicable here, because this
function takes regular pointers and not __iomem ones. You'll either
have to copy the data in an intermediate buffer before calling
nand_check_erased_ecc_chunk(), or cast the SRAM region to a void
pointer (which is usually not a good idea). The last option would be to
open code nand_check_erased_ecc_chunk(), but I'd really like to avoid
that (for maintainability concerns).

[1]http://lxr.free-electrons.com/source/drivers/mtd/nand/nand_base.c#L1414

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