s3c244x hardware ecc / backup kernel and rootfs direction

Andy Green andy at openmoko.com
Wed Aug 13 19:22:41 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:

| However, I think we should do ECC error correction also in the
| kboot loader, because NAND performance is only guaranteed for
| correctable errors (i.e., single-bits), but not for the raw
| memory. (I guess this makes you like NAND yet a little less ? ;-)

I knew about the general ECC crap already and already adjusted my love
of raw NAND accordingly.

| By the way, for "kboot" userspace, it's interesting to follow what
| the PS3 Linux project is doing since they've been using kboot for
| a while. It turns out that they've abandoned kboot and now have
| something called petitboot:

I referred to this as "kboot" for want of a better name.  Rather than
buy into any meaning from that, to me, this is simply the "minimal shim
to run Linux".

| http://ozlabs.org/~jk/projects/petitboot/

| Given that the shell features of kboot wouldn't be terribly useful
| in everyday use on our devices anyway (Petitboot has a shell

What shell features?  Shell features in bootloader are evil.

| escape, so no functinality is lost), I think we should try to make
| Petitboot work as our main "kboot" interface. (That is, in
| non-fastpath mode.)

Having been through rootfs creation with DM2, I think the winning way to
make this secondary rootfs is from the pieces we build be main rootfs
from.  That's the only way we deal with a single, living, unitary system
whether backup or main rootfs.  Put another way, the backup rootfs
uplevels with the packages from the main rootfs without us having to
deal with it.

So rather than introduce a new project / empire / *boot, I think we
should re-use our existing Linux packages to form the backup rootfs as a
not-a special-case-at-all but a restricted packageset backup filesystem
in NAND.

- -Andy
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