[U-Boot] CONFIG_PRAM and CONFIG_SYS_MEM_TOP_HIDE ?

[Joakim Tjernlund]

Just started to look at reserving some RAM from u-boot and the kernel
and got a bit confused about what config options to use.
I found CONFIG_PRAM and CONFIG_SYS_MEM_TOP_HIDE and from what I can tell
one needs to set both to hide some memory from both u-boot and linux
but CONFIG_SYS_MEM_TOP_HIDE is PPC only so that doesn't feel right.
CONFIG_PRAM sets the env var. "mem" but that is all(I think)

How is CONFIG_PRAM supposed to work? Should the reserved memory be
subtracted from the memory passed to linux via the device tree?

       Jocke