Regarding UBI fastmap data CRC failure

[Richard Weinberger]

Ronak Desai,

Am 21.03.2017 um 17:31 schrieb Ronak Desai:
> On Mon, Mar 20, 2017 at 5:56 PM, Richard Weinberger
> <richard.weinberger at gmail.com> wrote:
>> On Mon, Mar 20, 2017 at 10:47 PM, Ronak Desai
>> <ronak.desai at rockwellcollins.com> wrote:
>>> Hi All,
>>>
>>> In one of the products with MLC NAND flash, we are using UBI
>>> filesystem with kernel 3.12.
>>
>> MLC NAND is currently not supported.
> 
> First of all, thanks for your response and your truly amazing
> contribution in UBI.

Thanks. :-)

> I know that UBIFS requires a whole lot of changes to handle "program
> disturb", "read distrurb" and "paired pages" problem on MLC NANDs.
> But, apart from this, we have makesure that we use 256 wear-leveling
> threshold.

How do you handle paired pages?
A powercut can still damage UBI and UBIFS.

[...]

> That is true that our kernel is old but at this point and time it's
> not a viable options for us to upgrade the kernel version. And agree
> with your point about MLC but in months of use, we have seen this
> continuous fastmap failure issue only once and apart from that UBIFS
> works without any other issues.
> 
> I see your changes on base fastmap implementation, which I am planning
> to backport but it will be really difficult to backport the whole UBI
> subsystem. So, if you can point to specific patches/changes to avoid
> "fastmap data CRC failure" issue then it will be a great help.

I fear it is not that easy. Fastmap saw many fixes and improvements
other the time. The first version was rather buggy.
And we made a stupid mistake at the beginning, we did not mark fixes
for stable processing since Fastmap was considered
as experimental. That's why you can't just backport all patches that
have a stable tag.
On the other hand, backporting the whole UBI subsystem is not that
complicated. It has very few dependencies.
U-Boot folks do this on a regular basis.

HTH,
//richard