[RFC PATCH 1/4] ARM: kernel: add device tree init map function

On Wed, Nov 07, 2012 at 12:00:52PM +0000, Lorenzo Pieralisi wrote:

On Wed, Nov 07, 2012 at 11:05:42AM +0000, Will Deacon wrote:

quoted

No, I was thinking about what happens if the devicetree doesn't contain an
mpidr property that matches the boot cpu. In this case, we will fail to
assign logical ID 0, right? If this happens, we should complain about an
invalid devicetree and try to fall back on the logical_map that was
generated earlier on.

Good point. What I could do, I can assign the MPIDR of the boot CPU to
the logical index 0 before even starting to parse the DT (that's what it
is done in smp_setup_processor_id(), with a couple of twists). Then, if I
find a node that matches the boot CPU mpidr I just skip over it. This
way the boot CPU MPIDR will always be correct the only difference with
the current approach will be that instead of generating the secondaries
MPIDRs we will read them from DT.

That should work, although I'm not sure why you can't just give up
altogether and use the initial mapping from smp_setup_processor_id?

The problem with this approach is that if we need a pointer (phandle) to the
boot CPU DT node through the MPIDR and the boot CPU node is botched or missing
we still behave as if the DT CPU nodes were ok.

Does any code do this? Wouldn't it be much better to lookup logical CPU 0 if
you want to find anything out about the boot CPU?

I think I'd better stick a warning condition in there if the boot CPU
node is not present or botched (from a MPIDR perspective at least).

Definitely!

Will