[PATCH 4/6] arm64: topology: add MPIDR-based detection

Mark Brown broonie at kernel.org
Fri May 16 11:39:15 PDT 2014

On Fri, May 16, 2014 at 05:34:04PM +0100, Sudeep Holla wrote:

> This is broken, IIRC Lorenzo commented on this in the previous version of the
> patch.

Could you please be specific?  Lorenzo was concerned about overflow but
that ought to be addressed here.

> Take a simple example of system with 2 Quad core clusters.
> The mpidr_hash.shift_aff[1] will be 6 as you need minimum 2 bits to represent
> aff[0]. So you will end up with second cluster with id = 4 instead of 1.

This isn't a problem, the clusters can have any numbers so long as they
are distinct.  There is no other requirement.

> I am not sure if we need this serialization, but even if we need it you can't
> simply use the hash bits generated for MPIDR.Aff{3..0} serialization directly
> as is for serializing parts of it.

Ah, now I look at what the hash is doing that is indeed directly useful
- we can mask or shift out the bits we don't want.  Equally well it just
looks like a preference?

This does seem like something that could be dealt with incrementally.
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