[U-Boot] Support of device-tree for PowerPC platform: Query

[York Sun]

+Simon

On 06/27/2018 01:05 AM, Prabhakar Kushwaha wrote:
> Hi All,
> 
> We are trying to add support of device-tree for PowerPC platforms. As per our analysis following 2 options can be used. 
> 
> a) CONFIG_OF_SEPARATE 
> b) CONFIG_OF_EMBED
> 
> In PowerPC platforms, reset_vector is always expected at the **last** address of flash.  
> U-boot binary has reset_vector at last followed by __bss sections(not present in binary) and must be programmed in such a way that reset_vecrot lie at **last** address of flash.  
> 
> Hence dtb cannot be appended at last of  u-boot binary.
> 
> So there looks to be following 2 possible solutions
> a) Use CONFIG_OF_SEPARATE and append dtb at start of u-boot binary.  This require change in flash map because u-boot start address needs to shifted (due to reset_vector requirements).
>      Exiting offset of env and fman ucode also needs shifting. This approach requires modification in almost all existing PowerPC platform to adhere to new **modified** flash map.
> 
> b) Use CONFIG_OF_EMBED and embed dtb inside u-boot. This way no change in exiting flash map. But its usage is being discouraged as per doc/README.fdt-control.
> 

Clearly putting dtb at the very end doesn't work, neither last 4KB. I
think we either use CONFIG_OF_EMBED (many boards use this way), or try
"fdtcontroladdr".

York