[U-Boot] [RFC][PATCH 3/3] Add board support for the eXMeritusHWW-1U-1A devices

[Moffett, Kyle D]

On Sep 07, 2010, at 17:40, Peter Tyser wrote:
> Hi Kyle,
>> The latest u-boot.git still seems to have the P2020DS lines that I referenced in "Makefile", and it has no references at all to "P2020DS" in the "boards.cfg" file.
> 
> It looks like the top-level Makefile is still required for boards that
> support multiple configs, eg 'make P2020DS_36BIT' will configure U-Boot
> to compile a 36-bit addressable U-Boot image while 'make P2020DS' will
> configure a 32-bit addressable U-Boot image, but they both use the same
> Makefile rule with some fancy parsing.  So I guess if you have a need
> for both a 32 and 36bit version of U-Boot you'll to modify the Makefile
> like your original patch did unfortunately.  If you don't need to
> support both U-Boot configs, you can go the route of other similar
> boards that are only in boards.cfg, eg P4080DS, P1022DS, XPedite5370,
> etc.

Hmm...  Well I'd like to just have my config always be 36-bit to support up to 4GB of RAM.  On the other hand, I also still need to support 32-bit kernels (with only 2GB of usable RAM, obviously).  Unfortunately right now I don't see any way of doing both from the same U-Boot image and device tree, as a 36-bit U-Boot maps critical I/O much higher in physical address space.

This leads to another question: Is there any way to create a memory hole just like x86_64 systems do?  Specifically, I'm thinking about a physical memory-map like this:

   0x00000000 -  0x7fffffff [  2GB]  DDR2 Memory
   0x80000000 -  0x9fffffff [512MB]  PCIE3 Window
   0xa0000000 -  0xbfffffff [512MB]  PCIE2 Window
   0xc0000000 -  0xdfffffff [512MB]  PCIE1 Window
   0xe0000000 -  0xefffffff [256MB]  FLASH (2x128MB)
   0xf0000000 -  0xffffffff [256MB]  Miscellaneous I/O resources
  0x100000000 - 0x17fffffff [  2GB]  DDR2 Memory, inaccessible to 32-bit OS

This is basically the same as my current 32-bit memory mapping, but with all memory above 2GB mapped separately further up in the address space.