On 08/07/2014 01:55 AM, Grazvydas Ignotas wrote: > On Wed, Aug 6, 2014 at 11:02 AM, Roger Quadros <rogerq@xxxxxx> 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@xxxxxx> 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@xxxxxxxxx> > > Found something new in dmesg though: > [ 1.542755] nand: device found, Manufacturer ID: 0x2c, Chip ID: 0xbc > [ 1.549621] nand: Micron MT29F4G16ABBDA3W > [ 1.553894] nand: 512MiB, SLC, page size: 2048, OOB size: 64 > [ 1.560058] nand: WARNING: omap2-nand.0: the ECC used on your > system is too weak compared to the one required by the NAND chip > > Do you think it's best to migrate to different ECC scheme? It would be > better to avoid that so that users can freely change kernels and the > bootloader wouldn't have to be changed.. > I'm not sure why these boards were using Software ECC scheme in the first place. So moving to a better ECC scheme should be considered with a warning that backward compatibility will be broken. There is a limitation with the OMAP3 ROM code loader. So if you want uniform ECC scheme for MLO, u-boot and kernel partitions then we are limited to Hamming code for SLC NAND with 512B, 2KB and 4KB pages. For MLC NAND, the ROM code uses a proprietary layout using checksum and BCH and I'm not very sure if this is compatible with the newer OMAP platforms and AM33xx platforms. For details see OMAP35x TRM. (spruf98y.pdf) http://www.ti.com/lit/ug/spruf98y/spruf98y.pdf sections 25.4.7.4.2 SLC NAND Read Sector Procedure 25.4.7.4.3 MLC NAND Read Sector Procedure cheers, -roger -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
