Re: [PATCH 10/17] bootwrapper: Add dt_set_mac_addresses().

[Jon Loeliger <jdl@freescale.com>]

On Wed, 2007-03-21 at 19:06, David Gibson wrote:

> I mean, does the u-boot source tree have its own copies of the dts
> files which are built into a dtb during the u-boot build process?

There are not DTS files in U-Boot anymore.  They are all
currently in the arch/powerpc/boot/dts directory, or some
other private home directory. :-)


>   Or
> do you take the dts from the kernel tree and make the dtb from that

yes.

> when you build a dtb aware u-boot for a particular machine?

Do it whenever you want.  But it has to be downloaded
to RAM or found in flash on the board by U-Boot by the
time you want to do the hand-off to Linux.  That is,
there is no need to "combine" it with U-Boot to make
it "dtb aware".  U-Boot is still built independently of
any DT[SB] file entirely.


> > Ok, I understand now, but I don't know what value it has.  I don't see 
> > the difference, from the DTS point-of-view, between
> > 
> > 	local-mac-address = [ 00 00 00 00 00 00 ]
> > and
> > 	local-mac-address = [ ? ? ? ? ? ? ];
> 
> In terms of the generated dtb output there is no difference.  Well,
> probably.  It would It's
> purely syntactic sugar / internal documentation.

Right.  It is more like "make it clear to the DTS file
reader that these fields are intended to be filled in by
the bootloader".


> Well, no.  You wanted to get rid of the property from the dts, I
> didn't.  What I'm suggesting here is an idea to addresses at least one
> possible objection to having the properties in the dts: the fact that
> with actual values there it looks like the tree is complete and it
> might not be obvious that a bootloader *must* tweak values to produce
> a working tree.

(nit) But let's not forget that there are cases where we _do_ want
the DTS to be complete too.

> I think it's useful to document in the dts that certain properties are
> expected to be there, even if their actual values have to be
> determined during boot.  This syntax allows a dts to show to someone
> reading it that a property is expected, and what its expected size is,
> but that the value must be filled in later.  It's for the benefit of
> people reading the dts, not programs.

Exactly.

jdl