[RFC 3/3] powerpc: Add DTS file for the Motorola PrPMC2800 platform

[Mark A. Greer]

On Thu, Mar 29, 2007 at 02:48:47AM +0200, Segher Boessenkool wrote:
> > That does seem like a lot.  The only thing that should need
> > virtual-reg properties is serial ports.  In fact, specifically, only
> > serial ports that the zImage is actually expected to use.
> >
> > In fact, with Scott's addition of xlate_reg() to the bootwrapper,
> > virtual-reg should only be needed on systems that enter the zImage
> > with MMU on.
> 
> Even then, you can just query the MMU structures to
> find out the currently set up translations for that
> physical address.  Way more robust.

Yes, that is the most robust but its also more complicated.
A higher authority will have to make that call.  In the meantime,
a patch would be useful to see just what it would take.

> The only valid reason to use "virtual-reg" is as a
> hack to map some device to get some debug output out.

Not true, its for more than just output.
See my response to David's email.

> If for normal usage you can't be bothered to parse
> the current translations, you probably shouldn't be
> doing anything as "advanced" as device I/O either --
> just boot the kernel and let it handle it ;-)

Well, the overall idea is that we remove boot/init related code from the
kernel and leave it to the firmware or the bootwrapper (if the firmware
doesn't provide the required functionality).  For example, the VPD code
in .../boot/prpmc2800.c in my patches.  Also, at one time there was code
to get the MAC addr from i2c prom and stick it in the dt.  I can see
that being fairly common for non-OF/uboot platforms.

> That said, I sure hope the kernel isn't using this
> property as well...

It certainly shouldn't be.  Its a bootwrapper-only hack.

Mark