[U-Boot-Users] Ideas on U-Boot configuration with FDT

Wolfgang Grandegger wg at grandegger.com
Fri May 18 16:44:02 CEST 2007

Timur Tabi wrote:
> Wolfgang Grandegger wrote:
>>      CPU:  MPC5200 v1.0, Core v1.1 at 396 MHz
>>            Bus 132 MHz, IPB 66 MHz, PCI 33 MHz
>>      FDT:  FDT_ERR_BADMAGIC (or OK, or version number?)
>>     At this level also the compatibility of the FDT tree could be checked
>>     using fdt_boardcheck().
> I think fdt_checkboard() (or boardcheck) should be run from inside the 
> fdt_open_into() command.  This takes advantage of the existing mechanism 
> of fdt_open_into() to return an error.  It also allows for a device tree 
> to be opened after U-Boot has booted.

But it's too late for initial initialization (before RAM is available). 
Using the FDT directly from ROM is not recommended because access might 
be slow, but we likely need it for early initialization.

>> - After relocation, the blob is copied into memory via fdt_open_into()
>>    to a defined place and "fdt" is updated accordingly. 
> So we'll need to have CFG_FDT_ADDR_FLASH and CFG_FDT_ADDR_RAM.


>> Not sure, what
>>    location in RAM to use, but it should fit into the existing scheme.
>>    Any recommendations?
>> - When U-Boot is up, "fdt" points to a valid FDT, e.g. "fdt addr" is not
>>    necessary.
> I think this feature needs to be optional.  That is, if CFG_FDT_ADDR_xxx 
> are defined, then we can enable this feature.  Otherwise, fdt_addr will 
> still be necessary.  Remember, we'll still need to support architectures 
> that don't have device trees.

Exactly, that's also what I meant.


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