Allow dtc to decompile device tre blobs in hexdump format

[David Gibson]

On Sun, Apr 04, 2010 at 12:30:15AM -0600, Grant Likely wrote:
> On Sat, Apr 3, 2010 at 10:22 PM, David Gibson
> <david at gibson.dropbear.id.au> wrote:
> > When debugging handoffs between different boot stages which use
> > flattened device trees to communicate, it's often useful to dump the
> > device tree blob being passed and use dtc to decompile it to something
> > readable.  However, with some debugging tools it's possible to perform
> > a hex memory dump of the device tree, but it's awkward or impossible
> > to directly dump the memory as a binary blob.
> >
> > Obviously, it's quite straightforward to write a script or program to
> > convert the hex dump back to binary, but I'm not aware of a standard
> > tool to do so.
> >
> > This patch, therefore, adds a "hex" input format to dtc which allows
> > it to directly (or almost so) parse and decompile a device tree blob
> > supplied as a hex dump.  The input dtc expects in this mode must have
> > no addresses or other extraneous text which could contain valid hex
> > digits, however it will silently ignore any whitespace, punctuation,
> > or other non-hex-digit formatting in the dump.  The dump must also
> > either be either byte-by-byte, or display each hex number as
> > big-endian (so "od -t x1" will produce suitable output on any system,
> > but "od -t x2" will produce suitable output only when run on a
> > big-endian system).
> >
> > Thus, if addresses and any header/footer are removed (usually easy to
> > do in an editor), dtc will accept quite a wide range of likely hex
> > dump formats.
> 
> Does it really make sense to build marshaling tools into dtc itself?

Well.. is it essential that dtc do this?  Clearly not.  Is it a
sufficient convenience that it's worth it?  Maybe.

> I think it would make more sense to keep transformation tools
> independent.  ie. what if I have srecord format?  or intel hex?  

If they're a) sufficiently widely used, b) not to hard to implement
and c) there aren't widely used existing conversion tools then I would
have no problem with adding support for such formats to.

> A
> trivial python or perl script would do the job for raw hex.

I've written that trivial python or perl script too darn many times,
and I'm sick of it.  I can't be the only one.

>  The
> ascii2binary tool should also work.  Also, objcopy handles
> srecord/ihex conversion beautifully.

Ah, I wasn't previously aware of ascii2binary.  If it's flexible
enough, that might well undermine the justification for this patch.

> I don't think it makes sense to be teaching dtc different
> representations of the same dtb format.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson