[coreboot] [PATCH]Disable failover in K8 based boards

Myles Watson mylesgw at gmail.com
Wed Aug 12 23:38:38 CEST 2009

> fallback/normal was a fine solution for pre-CBFS images. I'm not
> convinced it still is.
In that case what you're proposing is moving to fallback-only.  That's one
more step, right?

> A safe update method is the main use case for fallback/normal I've heard
> about so far.
Another use case is hardware (an FPGA in my case) that might be
misconfigured.  If it is, the boot fails several times and uses the

It seems like both Ron and Stefan thought the dual image solution was
necessary at one point.  I don't remember their rationale.

> With CBFS, updating an image is harder than before. pre-CBFS, you could
> simply dd(1) the old and the new image in some ways and get a new image
> with a new normal image and an old fallback image. With CBFS, you don't
> have such a clean alignment of the data inside the image, so you'll have
> to extract the pieces and add them to the other image.
That's fine as long as cbfstool works.

> The other thing fallback/normal is used for is CMOS-aware code with
> recovery if CMOS is invalid. But it's flawed as it is: When the "normal
> image" bit is set correctly, and everything else is wrong, normal is
> run, and probably hangs (it did for me).
Then if you reboot enough times it goes to fallback as long as the failover
code isn't broken.

> What _should_ happen (in my
> opinion) is that we use the CMOS checksum, and have the same code use a
> static field (somewhere in ROM) as a backup if the CMOS values can't be
> trusted.
> That could work by extending the cmos.layout file with defaults that are
> written to some static C array, which is linked in. get_option (I think
> that's what the CMOS access code is called) switches between CMOS and
> this table based on the CMOS checksum. This is more stable than the
> current approach and gets rid of a second binary 
This seems orthogonal to me, but it seems like a good idea.

> (probably with
> different behaviour beyond the config values!)
By design, right?
> What other use cases for fallback/normal are there that must be
> accounted for?
I don't know.  Fallback only is definitely simpler.

> > In general removing features is easier than adding them.  Will this make
> it
> > easier to add it later?
> >
> The change can be reverted with little effort: set
> CONFIG_HAVE_FAILOVER_BOOT to 1, add failover to the Config-abuild.lb
> again, and it works as it does now. I didn't remove the #ifs for
> FAILOVER etc. to easily figure out what parts of the code are "early
> setup" and what's later code, so we can reuse it, should we want to.
No problem.  I think this is the right time to have this discussion.


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