Re: acpivga(4) v. MI display controls

[Martin Husemann <martin%duskware.de@localhost>]

On Sat, Oct 16, 2010 at 11:28:33AM +0300, Jukka Ruohonen wrote:
> I do not know OF well, but my impression is that it is much, much less
> invasive than what we have nowadays on x86 where close interaction between
> the firmware and drivers are expected.

Indeed. Quentin once tried to explain to me why autoconfig is so much harder
with ACPI than with OF, but I failed to get the big picture.

The main difference that I understood seems to be what you call virtual
and natural device trees: in OF world we guide the whole autoconfig tree
along the OF device tree, with differences close to the leafs (i.e. the
scsibus der Mouse mentioned). At every point during autoconfig we can
make sure to have enough OF information already available during the
device_register() call. The only problem we ran into so far, IIRC, is the
id of FC disks for boot device detection, but we worked around that pretty
easily.

I don't think the auto-config time and in/out distinction you draw
realy is that relevant. With OF we still can call firmware methods any
time later, and we could take callbacks (though I don't think there are
any relevant). ACPI seems to do more in that area, but I fail to see the
fundamental problem, assuming you manage to get ACPI device tree traversal
and autoconfig tree building "synchronized" somehow (i.e. have all needed
ACPI information available for device_register()).

Martin