[coreboot] PC Engines APU2 support

[Gerd Hoffmann]

  Hi,

> > It seams the SeaBIOS prefer to use/promote sgabios instead of building it's own
> > serial input solution.
> > 
> > http://www.seabios.org/pipermail/seabios/2016-May/010677.html

> End users seems to have problems with sgabios and that's why I was asked
> to remove sgabios support. It looks like using Google sgabios is design
> decision,

You are talking about seabios?

No, it's not really a design decision.  It's just that sgabios works
good enough for most cases and thus there is little motivation to do the
work needed to fully replace sgabios.

So, feel free to submit patches.  The implementation must have
reasonable quality though.  It doesn't make sense to merge something
which is worse than sgabios.  See Kevin's note on vt100 sequence parsing
in the patch review linked above (scroll to the end).

Given that the sgabios input code isn't that great either it shouldn't
be difficult match it in quality.

<quote sgabios.S>
/*
 * multibyteinput
 *
 * When an escape key is detected, the input routines will attempt to
 * capture as many characters as arrive up until a timeout, or six,
 * whichever is less.
 *
</quote>

The approach chosen by sgabios works fine as long as you type slowly.
But if you hold down keys so autorepeat kicks in sgabios can't grok it
any more.  Try moving around the cursor quickly in the grub editor for
example.

I can imagine rewriting the whole thing in C for seabios is easier than
fixing the sgabios assembler code ...

cheers,
  Gerd