Request review of device tree documentation

[Grant Likely]

On Sat, Jun 12, 2010 at 4:52 PM, Benjamin Herrenschmidt
<benh at kernel.crashing.org> wrote:
> On Sat, 2010-06-12 at 06:30 -1000, Mitch Bradley wrote:
>
>> I'm certainly going to try keeping OFW alive.  On the x86 OLPC machines,
>> the ability to
>> dive into OFW via a SysRq key combo was very helpful for debugging some
>> difficult
>> problems.  The team has asked me to support the feature on ARM.
>
> Oh well, if you can and can convince the ARM kernel folks to do the
> necessary changes ... :-)

What is needed to keep OFW alive?  I've got no problem with doing so
if it isn't invasive, and as long as the same boot entry interface can
be used.

> One thing tho, you will only benefit from the whole infrastructure we
> have created accross platforms in linux if the device-tree is "sucked"
> into linux at boot. IE. Linux will not do constant accesses to OF for
> the DT. Even sparc converted to that now.
>
> That means that if your device-tree has a dynamic nature, we'll need to
> come up with a way to inform the kernel of changes in it so it can
> update it's copy accordingly.

What is the use-case for having a dynamic device tree?  I can see
keeping OFW alive being useful for some debug facilities, but once the
kernel has started, I'm really not interested in relying on firmware
to manage the hardware.  (but then again it's no secret that I'm
suspicious of anything that depends on runtime interaction with
firmware).

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.