Re: [RFT PATCH v1 0/4] Unify CPU topology across ARM64 & RISC-V

[Morten Rasmussen]

Hi,

On Thu, Nov 29, 2018 at 03:28:16PM -0800, Atish Patra wrote:
> The cpu-map DT entry in ARM64 can describe the CPU topology in
> much better way compared to other existing approaches. RISC-V can
> easily adopt this binding to represent it's own CPU topology.
> Thus, both cpu-map DT binding and topology parsing code can be
> moved to a common location so that RISC-V or any other
> architecture can leverage that.
> 
> The relevant discussion regarding unifying cpu topology can be
> found in [1].
> 
> arch_topology seems to be a perfect place to move the common
> code. I have not introduced any functional changes in the moved
> code. The only downside in this approach is that the capacity
> code will be executed for RISC-V as well. But, it will exit
> immediately after not able to find the appropriate DT node. If
> the overhead is considered too much, we can always compile out
> capacity related functions under a different config for the
> architectures that do not support them.
> 
> The patches have been tested for RISC-V and compile tested for
> ARM64 & x86.

The cpu-map bindings are used for arch/arm too, and so is
arch_topology.c. In fact, it was introduced to allow code-sharing
between arm and arm64. Applying patch three breaks arm.

Moving the DT parsing to arch_topology.c we have to unify all three
architectures. Be aware that arm and arm64 have some differences in how
they detect cpu capacities. I think we might have to look at the split
of code between arch/* and arch_topology.c again :-/

Morten