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

[Grant Likely]

On Thu, Jul 14, 2011 at 03:12:25PM -0400, David Long 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 should have everything you need to fix it.  If
CONFIG_SYS_BOOTMAPSZ is defined, then U-Boot will not use memory
larger that that for the dtb or atags.

Right now CONFIG_SYS_BOOTMAPSZ is not set by default, but we could
default it to a sane value for ARM platforms.

A better solution in the long term may be to figure out the actual
memory footprint required, and not make things any larger than that,
but that requires U-Boot to be given more data about the kernel, or
the zImage wrapper to be more intelligent about dtb and initrd ranges
when uncompressing

g.