Re: [PATCH 0/8] Generic serial earlycon

[Arnd Bergmann <arnd@arndb.de>]

On Sunday 23 March 2014, Rob Herring wrote:
> IIRC, the unflattening cannot be done before memblock is up which is
> in arm_memblock_init. I believe that will get done earlier similar to
> PPC with Laura's meminfo removal series. However, in interest of
> getting output enabled as early as possible, the earliest point is
> always going to be with a flat tree. So I think we do want to be able
> to parse the flat tree for this. There's code in u-boot to do the
> address translation on FDT we can steal. Really, i'd like to put that
> code in libfdt, but there's a licensing problem with the u-boot code
> being GPL and libfdt being BSD.

I suppose it depends on what the goal is. If you are trying to get as
close as possible to the debug_ll functionality without losing the
ability to turn it on unconditionally, I agree that it needs to be done
on the flat tree.

However, the goal that interests me more at the moment is to have
reliable debug output done in a simple way earlier than what we have
today with the normal console support. For this, it seems a better
tradeoff to initialize the early console slightly later. This
can actually be done independent of the the command line option,
I don't see any downsides from having a compile-time option that
would initialize the early console from setup_arch (after
unflatten_device_tree) whenever there is a linux,stdout-path
property that points to a usable device.

	Arnd