On 11/29/06, Jerry Van Baren gerald.vanbaren@smiths-aerospace.com wrote:
Ben Warren wrote:
Hi Jerry,
On Wed, 2006-11-29 at 09:01 -0500, Jerry Van Baren wrote:
- 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.
s/selected/chosen/