[coreboot] Boot flow flexibility changes

[Aaron Durbin]

Hi Folks,

I just wanted to point out to people that I posted changes to make the
boot flow more flexible:

http://review.coreboot.org/3131
http://review.coreboot.org/3132
http://review.coreboot.org/3133
http://review.coreboot.org/3134
http://review.coreboot.org/3135
http://review.coreboot.org/3136
http://review.coreboot.org/3137
http://review.coreboot.org/3138
http://review.coreboot.org/3139

The reason for these changes stems from dependency requirements on
newer machines that don't closely follow the device tree and pci
device ordering. However, there are other benefits such as dynamically
deciding to perform something at a given time during the boot sequence
as well as not introducing board-specific calls throughout the common
code. The patches provide usage examples by some of the core pieces of
code.

There is something else I've been thinking about and working on is the
ability to schedule work based on time. Ron had introduced a
microsecond global timer. There is also a desire on my part to utilize
this concept so that the boot flow isn't busy waiting on something
that takes a long time. I have the timer scheduler written, but it
requires global time source. On x86 this is quite complicated in that
there appears to be quite a few (> 3?) implementations of the udelay()
function. The timer scheduler would integrate into the boot state
machine above by running the timers between states. Additionally, the
concept of blocking state entry when  timers are queued. That concept
would provide a sequence point for not proceeding further than
necessary until all work is drained.

I wanted to get people's thoughts on these concepts. I think I can
push off the introduction of the timer scheduler by just delaying work
using the boot state machine. However, I'm not sure what other
people's needs are.

Thanks.

-Aaron