Re: NAND review

[Gary Thomas <gary at mlbassoc dot com>]

Ross Younger wrote:
> Gary Thomas wrote:
>> I don't know what/where you were looking to come to these conclusions :-(
>> Linux MTD has had the ability to use the RedBoot FIS directory for many (7+) years.
> 
> At the moment, as I understand things, FIS implies io/flash, which pretty
> much implies NOR. I don't have any plans to implement FIS on top of NAND;
> people who do use NAND will generally be using a filesystem, so "obviously"
> the right place to put static config data is on that filesystem? (Chicken,
> meet egg?)

I implemented FIS on NAND on the MOAB board in 2002 - it has been in the eCos tree
since then.  This also supported Linux 2.4 in the same time frame (the company
that made the MOAB is out of that business, so that port has fallen by the
wayside, but it has been done before, for a long time)

And yes, that support was built on top of io/flash - not perfect and I'm
not saying that the current discussion is out of line, but [IMO] proper
partition support using RedBoot FIS on NAND is not a new idea.

As for what to do if the block(s) containing the FIS directory are bad - this
is a day-one problem for all such systems.  That's why your EXTn file system
writes out many "super blocks" so there is a fall back, etc.  If there is a
bad blocks replacement algorithm, use that (Linux MTD has pretty strong ideas
about this for NAND which I suggest you follow), otherwise find another way
to deal with such failures.

> Now, if we were to need to write a primary bootloader - say, if a
> OneNAND-based SOC came into the frame and we wanted to run RedBoot on it -
> then we might very well find ourselves needing something along these lines.
> A very very simple filesystem, combined perhaps with the ability to store a
> little config data and/or partition table layout, for which it might be
> worth considering reusing some or all of the FIS code? With that in mind, I
> suppose that defining a scheme for a partition table and very simple FS for
> NAND would be a worthwhile exercise, which could then of course be
> contribbed to Linux. Comments?

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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