[U-Boot-Users] RFC: flattened device tree command

Grant Likely grant.likely at secretlab.ca
Wed Nov 29 17:03:09 CET 2006

On 11/29/06, Jerry Van Baren <gerald.vanbaren at smiths-aerospace.com> wrote:
> Ben Warren wrote:
> > Hi Jerry,
> >
> > On Wed, 2006-11-29 at 09:01 -0500, Jerry Van Baren wrote:
> >
> >> 2) I see more commands than just dumping the tree, allowing the user to
> >> manipulate the tree as well.  My current thoughts are to make a new
> >> command "fdt" (flattened device tree - the Open Firmware genesis appears
> >> to be depricated) with subcommands like the existing "mii" command.
> >>
> >> fdt read <node> - does what my "oftdump" command does
> >> fdt write <node> <value> - allow patching the fdt
> >>    * Writing could get pretty complex with creating nodes
> >>    * Initial implementation would be simply to change existing values
> >>
> >
> > A naive question, to be sure:  Do you really forsee wanting to change
> > the device tree from the U-boot prompt?  I can see value in dumping the
> > contents and having an API that board-level boot code can use to modify
> > the tree.  Maybe for initial board debugging it would be useful to try
> > things out quickly, but modifying the quite-readable .dts files and
> > recompiling doesn't take long either.
> >
> > Again, I don't mean to be critical - I'm just curious where you envision
> > this being used.
> >
> > regards,
> > Ben
> It goes with the classic unix/C philosophy of providing enough rope to
> shoot yourself in the foot. ;-)

this is supposed to be a mixed-metaphor free zone.  :-P

> Seriously, I don't have any concrete examples, but the current "bootm"
> command autogenerates values that are added to the tree, and also
> (optionally) adds the u-boot "env" values.  The env values can be
> changed via the env commands, but the autogenerated values currently cannot.

ie. change the enumeration of serial ports (via property values).  I
have client boards where this would be useful at run time.

> One autogenerated node is the "selected" node.  I would contend that
> this should _not_ be autogenerated.  (The copy of dtc that I am using
> complains because my .dtc file does not have a "selected" node.)  If you
> had multiple CPUs and wanted to boot from a different one, it would be
> really nice to be able to do that interactively or script it via hush.


Grant Likely, B.Sc. P.Eng.
Secret Lab Technologies Ltd.
grant.likely at secretlab.ca
(403) 399-0195

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