[U-Boot] [PATCH v2] common: fit: Allow U-Boot images to be booted

[Robert P. J. Day <rpjday@crashcourse.ca>]

On Wed, 20 Jul 2016, Mario Six wrote:

> On Wed, Jul 20, 2016 at 3:56 PM, Robert P. J. Day <rpjday@crashcourse.ca> wrote:

... snip ...

> >   not really, since i always thought that the difficulty in loading
> > and booting a second-stage u-boot was explained here:
> >
> > http://www.denx.de/wiki/view/DULG/CanUBootBeConfiguredSuchThatItCanBeStartedInRAM
> >
> > that is, loading the second image to a different address is simple;
> > the apparent difficulty is that the second-stage u-boot might not be
> > able to handle the early setup already done by the first stage.
> >
> >   so i'm still confused as to what is being proposed here, and how it
> > works.
> >
> > rday
> >
>
> Ah, alright. Look at the following quote from the page:
>
> "On machines with boot-ROM and U-Boot-SPL, you might have better luck."
>
> I'd venture that most SoCs these days have a boot-ROM; on these
> U-Boot, is not as sensitive to not finding a "virgin" system
> (because the boot-ROM does some initialization beforehand). The
> system I tested with is a Armada 38x, and we've also use a similar
> approach on a MPC85xx system (if you would like to dig that deep,
> the code is upstream: board/gdsys/p1022/controlcenterd*). The whole
> SPL concept would be a problem if the boot loader needed a virgin
> CPU (since, well, the SPL *is* a second U-Boot), so the restrictions
> mentioned in the page are not as relevant for modern SoCs.
>
> That's as far as my knowledge goes, if anyone wants to correct me,
> you're welcome to do so :-)

  ok, so it appears that wiki page is a little on the pessimistic
side, then. i was aware of the SPL, having worked with beaglebone
black for a while. i've never looked *closely* at how limited or
restrictive the SPL is, but i did know it had to do far less than the
full-featured u-boot. maybe it's time to look into that far more
closely to understand it better, and to appreciate what's possible.

  i can see this 2013 presentation, "TPL: SPL loading SPL (and, SPL as
just another U-Boot config", from scott wood of freescale. that looks
like it might be educational.

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
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