[RFC 0/1] use lmb to calculate ram left for the kernel

[Tomas Alvarez Vanoli]

>>I am confused here. You mention above that the address of the rootfs is determined based on its size. So you do know the memory that would be needed for the rootfs? Also, how does calculating the amount of RAM left over for the kernel help. I mean, what if the kernel is bigger than the amount of left over memory? Can that not happen if you don't know the amount of memory that would be needed for the kernel as you mention above.

>Sorry, maybe I misused the term "kernel memory". I am referring to the amount of physical ram available for the kernel to use:
> ....
>I hope this clears up the usecase.

Some extra info for the design decision, sorry for the double post, I hope this makes the situation more clear:

- This is used for development purposes only, if somehow the ram given to the kernel is not enough it's not a problem, it will crash (it was happening after the u-boot update because the tftp allocated regions were not considered free, and it was giving the kernel very little memory).

- It will always be enough if it's calculated correctly. Boards have between 1 and 2 GB of ram and the rootfs is typically 30 to 50MB.

- Previously this was calculated manually by subtracting reserved region sizes, but since the introduction of our armv8 boards it became simpler and more generic to use lmb.

- using this instead of nfsroot lets us have multiple boards of the same type downloading the same rootfs. With nfs, we would need to point each board to a different nfsroot to avoid collisions.

Tomas