of: reserved_mem: Try to keep range allocations contiguous

of: reserved_mem: Try to keep range allocations contiguous

Right now dynamic reserved memory regions are allocated either
bottom-up or top-down, depending on the memblock setting of the
architecture. This is fine when the address is arbitrary. However,
when using "alloc-ranges" the regions are often placed somewhere
in the middle of (free) RAM, even if the range starts or ends next
to another (static) reservation.

Try to detect this situation, and choose explicitly between bottom-up
or top-down to allocate the memory close to the other reservations:

  1. If the "alloc-range" starts at the end or inside an existing
     reservation, use bottom-up.
  2. If the "alloc-range" ends at the start or inside an existing
     reservation, use top-down.
  3. If both or none is the case, keep the current
     (architecture-specific) behavior.

There are plenty of edge cases where only a more complex algorithm
would help, but even this simple approach helps in many cases to keep
the reserved memory (and therefore also the free memory) contiguous.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20230510-dt-resv-bottom-up-v2-1-aeb2afc8ac25@gerhold.net
Signed-off-by: Rob Herring <robh@kernel.org>