Booting PPC Linux

Renaud Barbier renaud.barbier at
Fri Mar 2 11:28:15 EST 2012

On 01/03/12 20:07, Sascha Hauer wrote:
> On Thu, Mar 01, 2012 at 07:41:35PM +0000, Renaud Barbier wrote:
>> I have a uImage + dtb that use to boot on a MPC8544-like system
>> a few months ago.
>> After rebasing my code, it did not work.
>> I notice that in arch/ppc/lib/ppclinux.c the kernel is now called
>> with the device tree as a parameter.
>> After investigation, I copied the device tree to within 8MB of the
>> kernel entry point (0x0). It booted.
>> Is the DTB relocation a missing step?
> Yes, it seems so. barebox holds the device tree in malloced space. This
> is likely outside 8MB of the kernel entry point. I was not aware of that
> restriction.
I think I found the limitation in Linux.

In arch/powerpc/mm/init_32.c:

  * address of the limit of what is accessible with initial MMU setup -
  * 256MB usually, but only 16MB on 601.
phys_addr_t __initial_memory_limit_addr = (phys_addr_t)0x10000000;

The book E specific code (arch/ppc/mm/fsl_booke_mmu.c) adjusts this variable
  to 256MB but the highest I was able to  put the DTB is below 64MB.
It may be limited by another function call.

The available memory may be limited to 8 or 16MB on other CPUs (601 and 


> Sascha

Renaud Barbier
14, Links Place
3/2 great Michael House
Edinburgh, EH67EN
Tel: +44 131 561 3532

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