wrap around in a memory region property?

[AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>]

# This issue was raised from a discussion on my patch set of kexec_file
  support on arm64. Please see the thread[1] for the background.

Let's think about the case that we want to modify a device tree blob and
dynamically add a sort of "memory region" property to some node:
        mem_range = <addr size>;

When #address_cells == 1 and #size_cells == 1, how we should deal with
the memory if "addr + size" overflows a 32-bit range and wraps around?

One instance is (from Frank's email),
>	   / memory@0xfffff000 {
>		reg = <0xfffff000 0x2000>;
>	     }
>
>	or must it be specified as (option 1):
>
>	   / memory@0xfffff000 {
>		reg = <0xfffff000 0x1000 0x0 0x1000>
>	     }
>
>	or (option 2):
>
>	   / memory@0xfffff000 {
>		reg = <0xfffff000 0x1000>;
>	     }
>	     memory@0 {
>		reg = <0x0 0x1000>;
>	     }

Or does it imply, in fact,
    0x0fffff000-0x0ffffffff, and
    0x100000000-0x100000fff ?
(because neither #address_cells nor #size_cells, in theory, prevents
the host from having >32-bit memory space.)

I think that the current devicetree specification doesn't have
a clear definition (or restriction) in this point.

I will appreciate your comment/feedback.


 [1] httpe//lists.infradead.org/pipermail/linux-arm-kernel/2018-September/601762.html

Thanks,
-Takahiro Akashi