[U-Boot] [uboot PATCH v2] Add uboot "fdt_high" enviroment variable

[Scott Wood]

On Thu, 14 Jul 2011 15:12:25 -0400
David Long <dave.long at linaro.org> wrote:

> On Fri, 2011-07-15 at 03:50 +0900, Grant Likely wrote:
> 
> 
> > Regardless of this patch, the pandaboard uboot still needs to be
> > fixed. Setting an fdt_high variable is useful for debug, but it is not
> > a fix.
> > 
> 
> 
> Then someone needs to own the issue of stopping  the current u-boot
> default behavior of relocating the initrd and fdt to the end of RAM when
> an fdt is present.  This is an issue for any Linux ARM system with more
> than 3/4GB of RAM, and probably for other 32-bit architectures.   The
> logic that causes the problem is in architecture-independent code, and
> I'm not sure I'm necessarily the right guy to go rummaging around in
> there.  There are too many implications for any other currently
> supported targets that use u-boot and fdt.

You need to use lmb_reserve() to exclude any memory regions that are not
suitable for boot images -- see powerpc's arch_lmb_reserve() and
get_effective_memsize()/CONFIG_SYS_LINUX_LOWMEM_MAX_SIZE.

-scott