[U-Boot-Users] RFC: flattened device tree command
Jerry Van Baren
gerald.vanbaren at smiths-aerospace.com
Wed Nov 29 15:01:49 CET 2006
Wolfgang, Grant, and gentle readers,
A while back I submitted a patch for a new command "oftdump".
While it was good in principle, it probably is premature and short
sighted in implementation.
The command was hacked on top of ft_dump_blob() (common/ft_build.c) and
required some changes to the same. Grant objected to the changes as
suboptimal - I contend they are locally optimal, but that ft_build.c is
The linux kernel has its own library functions for
handling flat device trees. In addition, David Gibson has proposed
another library (advertised as easier to use):
My RFC has two parts:
1) Peoples' opinion of the relative merits of the current u-boot support
library vs. the kernel's library vs. David Gibson's library. My limited
experience with ft_build.c is that it is suboptimal. I don't have any
experience with the linux or David's libraries to form an opinion of them.
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
Related to the above discussion, the current ft_build.c/"bootm" code
takes the blob and augments it with board configuration and env stuff as
part of the "bootm" command. The implementation is suboptimal
(ft_build.c again) in that it is only done as a last thing before
"bootm" transfers to linux, making it (almost) impossible to dump and
definitely impossible to interactively poke around in the resulting fdt.
I would like to see this integrated done better in u-boot rather than
simply pasted onto the fdt at the last moment before jumping into linux.
So, in conclusion,
1) I'm not sure if this is truly a RFC or just a brain dump of my
current thoughts. Either way, advice is welcome.
2) Wolfgang: Please don't apply my "oftdump" command patch yet.
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