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

[dh at synoia.com]

 Duncan Hare

714 931 7952

     
----- Forwarded Message -----
 From: "dh at synoia.com" <dh at synoia.com>
 To: "u-boot at lists.denx.de" <u-boot at lists.denx.de> 
Cc: Cédric Schieli <cschieli at gmail.com>
 Sent: Sunday, November 13, 2016 4:08 PM
 Subject: FDT retrived varaibles appear to have different properties fom other u-boot variables - and are corrupted on get, set, get sequence
   
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=8250.nr_uarts=1 dma.dmachans=........all the boot args....... (note the space after "uarts=1)

 setenv abc $bootargs fails...as does printenv $bootargs

They I tried

fdt set bootargs /chosen bootargsfdt get value bootargs /chosen bootargsbootargs=8250.nr_uarts=1
The bootargs parameter list is truncated after the first blank.

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