[U-Boot-Users] U-Boot-NG ?

Wolfgang Denk
2007-07-04T19:36:55Z

Dear Robert,

in message <20070704184312.GI25364@pengutronix.de> you wrote:
>
> You have a better overview than I - can you estimate how many of the
> platforms u-boot supports are "embedded system like", i.e. SoC cpu,
> soldered RAM & NAND/NOR flash, vs. "PC like", i.e. you-need-to-initi-
> alize-the-north-and-southbridge-first-before-you-get-access-to-ttyS0?

In terms of board configurations most of them are "embedded" type. In
terms vof number of shipping systems the embedded ones outnumber the
others by a really, really huge factor.

> We agree on the fact that it is a pretty good feature to have early
> debugging, even before anything else works. It's just that, at the
> moment, it has the implication that the whole inner mechanics of u-boot
> cannot follow a simple device model, as proposed by our v2 code.

I wouldn't go as far as to say that. Maybe if the one-size-fits-all
approach does not work (at least not without hurting), then there is
still potential for a _compatible_ second approach? Who says the
"first step" *must* be as small as 4 kB, and *must* be in a
separately linked image, and *must* not link higher level functions
from the "real" U-Boot? Maybe both is possible, so everybody can
select the config he likes and be happy?

The thing is that there are many requirements which are pretty
complicated and sometimes contradicting:

- systems booting from NAND or dataflash etc. may require a very small
primary bootstrap loader
- systems with very limited resources may need a primary bootstrap
loader that unpacks the compressed U-Boot image
- dynamic switching of the console device may require early access to
the device tree
- allowing for a configurable console baudrate or for software-
adjustable CPU clock rates may require early access to the
environment
etc. etc.

What I would like to acchieve is an open discussion where none of
these requirements gets excluded just because it does not fit into
the currently preferred design model. Until a few days ago we had
only one code base to complain about. Now - thanks to Saschas
excellent work - we have two different implementations which we can
compare. This is an excellent chance to evaluate positions, to find
out what's good in one design or the other, and what should be
avoided.

If any feature is possible in the old design but leads to ugly code or
other issues, we should not simply drop it, but instead discuss how it
could be adapted for the other esign based on clean and beautiful (TM)
code.

> the next days and Sascha can show you some of the goodies. The longer
> one plays with the code, the more one gets the impression that it is
> simply plain elegant. It just makes POFF! and most of the spagetti code

I agree with that. And as far as I remember the previous discussion,
nobody ever raised any concerns or whatever.

> It would be a pita if the whole design wouldn't work just because of
> this early printk issue. So I hope we find a solution anybody can live
> with.

Agreed. The printf() thingy is just a problem that needs a solution,
it is not a killing point. It is not the only one - as mentioned
above, there are other things which I see difficult to implement in
the new code, not to mention the huge effort that will be needed just
to port a small fraction of the currently actively used boards. But it
wouldn't be software if all was easy and just working ;-)

> > Define "corner case".
>
> Use cases which obviously never happened here but seem to be common to
> you.

Please note that what you seem to consider corner cases are real
problems for some of our customers. And I have seen more than enough
casesmyself when a board stopped after printing "RAM: " (very often!)
or "Flash: " (still quie frequently). Please blieve me that I don't
want to discuss this to deat by raising artifical arguments. I am
serious.

Best regards,

Wolfgang Denk

--
DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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