Comment 14 for bug 707047

With DT present I see the regions described in the .dtb file being properly excluded. So now the problem is that just under 3/4 of available RAM is visible, when we should be able to see all except the 48MB set aside just below the 1/2G boundary (which is used by other processor(s) on the SoC).

The comment in the .dts file is not quite right. The top 256MB *is* (or can be) accessible with HIGHMEM condfigured. However, when DT is present the dtb data (and the initrd) are copied to the very end of SDRAM by uboot, and a pointer to that device tree location is passed into the kernel startup code. Apparently the kernel cannot handle device tree (and maybe initrd data too) residing in HIGHMEM.