[PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[Tony Lindgren]

* Grazvydas Ignotas <notasas at gmail.com> [140806 15:57]:
> On Wed, Aug 6, 2014 at 11:02 AM, Roger Quadros <rogerq at ti.com> wrote:
> > Hi Gražvydas,
> >
> > On 08/05/2014 07:15 PM, Grazvydas Ignotas wrote:
> >> On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq at ti.com> wrote:
> >>> For v3.12 and prior, 1-bit Hamming code ECC via software was the
> >>> default choice. Commit c66d039197e4 in v3.13 changed the behaviour
> >>> to use 1-bit Hamming code via Hardware using a different ECC layout
> >>> i.e. (ROM code layout) than what is used by software ECC.
> >>>
> >>> This ECC layout change causes NAND filesystems created in v3.12
> >>> and prior to be unusable in v3.13 and later. So revert back to
> >>> using software ECC by default if an ECC scheme is not explicitely
> >>> specified.
> >>>
> >>> This defect can be observed on the following boards during legacy boot
> >>>
> >>> -omap3beagle
> >>> -omap3touchbook
> >>> -overo
> >>> -am3517crane
> >>> -devkit8000
> >>> -ldp
> >>> -3430sdp
> >>
> >> omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
> >> booting mainline (I think it was 3.14) with rootfs on NAND, and while
> >> it did boot and reached a shell, there were lots of ubifs errors, fs
> >> got corrupted and I lost all my data. I used to be able to boot
> >> mainline this way fine sometime ~3.8 release. It's interesting that
> >> 3.14 was able to read the data, even with wrong ecc setup.
> >
> > This is due to another bug introduced in 3.7 by commit 65b97cf6b8deca3ad7a3e00e8316bb89617190fb.
> > Because of that bug (i.e. inverted CS_MASK in omap_calculate_ecc), omap_calculate_ecc() always fails with -EINVAL and calculated ECC bytes are always 0. I'll be sending a patch to fix that as well. But that will only affect the cases where OMAP_ECC_HAM1_CODE_HW is used which happened for pandora from 3.13 onwards.
> >
> >>
> >> Do you think it's safe again to boot ubifs created on 3.2 after
> >> applying this series?
> >>
> >
> > Yes. If you boot pandora using legacy boot (non DT method), it passes 0 for .ecc_opt in pandora_nand_data. This used to mean OMAP_ECC_HAMMING_CODE_DEFAULT which is software ecc. i.e. NAND_ECC_SOFT with default ECC layout. Until the above mentioned commits changed the meaning. We now call that option OMAP_ECC_HAM1_CODE_SW.
> >
> > Please let me know if it works for you. Thanks.
> 
> Yes it does, thank you.
> Tested-by: Grazvydas Ignotas <notasas at gmail.com>

OK thanks applying the whole series into omap-for-v3.17/fixes.

Tony