[U-Boot] FDT retrived varaibles appear to have different properties fom other u-boot variables - and are corrupted on get, set, get sequence

[dh at synoia.com]

Cédric
I move the fdt to 0x100
fdt move ${fdt_addr}  100
fdt addr 100

then
fdt get value bootargs /chosen bootargs
printenv bootargs 
bootargs=........all the boot args.......but setenv abc $bootargs fails...as does printenv $bootargs

fdt set bootargs /chosen bootargsfdt get value bootargs /chosen bootargsbootargs=bootargs
The variable name bootargs replaces the values contained in the variable bootargs in the fdt.
Something is not right in the world of fdt code.
 Duncan Hare

714 931 7952

      From: Cédric Schieli <cschieli at gmail.com>
 To: dh at synoia.com 
 Sent: Sunday, November 13, 2016 2:21 AM
 Subject: Re: Fw: [U-Boot] Fw: FDT pointer value, passed by the PI firmware, is not set in u-boot
   
Hello Duncan,

2016-11-13 3:04 GMT+01:00 <dh at synoia.com>:

> If appending to "/chosen bootargs" (making it longer), does the fdt command
> automatically relocate the fdt, or does the u-boot script have to do that
> itself?
>
> The fdt doc at http://www.denx.de/wiki/view/ DULG/UBootCmdFDT
> Is quite unclear on how the fdt size is managed, especially when the fdt is
> located close to the end of memory.

I'm not an expert here, but looking at cmd/fdt.c I didn't find any kind of relocation code. So I guess the safe bet is to move the blob before making any (growing) change to the tree:

# load the blob from the firmware provided address (at the end of memory)
fdt addr ${fdt_addr}

# move the blob to the (previously) default location (0x100)
fdt move ${fdt_addr_r}

# make needed changes
setenv bootargs "......."

# boot from the new location
bootz ${kernel_addr_r} - ${fdt_addr_r}


Another solution is to force the firmware to load the blob at a fixed location (as before) by updating config.txt:
device_tree_address=0x100

Regards,
Cédric