[U-Boot-Users] FDT intentions in u-boot

[Joakim Tjernlund]

On Wed, 2007-10-17 at 11:02 -0400, Jerry Van Baren wrote:
> Zach Sadecki wrote:
> > I have some confusion about FDT and what the intentions are for its
> > support and usage in u-boot.
> > 
> > From what I understand so far, u-boot only supports modifying a FDT
> > already loaded into memory.  Isn't this kind of an odd usage of a device
> > tree?  I thought a unique tree should be created for each hardware
> > implementation (a.k.a. system board) and therefore you shouldn't be
> > modifying it.  If changes are made a new device tree should be created.
> 
> You can only _modify_ a blob when it is in RAM.  You can store a blob in 
> ROM (flash) and copy it to RAM for modification.
> 
> If you don't need to modify the blob in order to boot linux, there is no 
> need (that I'm aware of) for loading/copying it to RAM.  *However* it is 
> unlikely that you (u-boot/linux) will be able to use an unmodified blob. 
>   For instance, the "chosen" node is (or should be?) generated by the 
> boot loader (u-boot) to let the kernel know about certain choices that 
> were made by the boot loader and/or the user.

OT, but I have always wondered how the chosen node is supposed to be
used. Would it be possible to specify which devices in the device tree
that should be used by the OS?
Supposed I got two boards that are identical, except one of them
does not have ethernet i/f. Would it be possible use the same device
tree for both boards, but tell OS that the ethernet i/f isn't present
on one of the boards?

I getting a bunch of boards thats are very similiar from the OS point of
view and I would like to just have one mega devtree and remove some
devices at runtime or change som properties.

 Jocke