Boot interface for device trees on ARM
Jeremy Kerr
jeremy.kerr at canonical.com
Wed Jun 9 00:26:13 EDT 2010
Hi Nicolas,
> > If we're planning to keep the machine IDs around (even if they are now
> > per- SoC), I'd like to know what would be left using them. The only
> > thing that I can see that we currently use is io_pg_offset for the
> > DEBUG_LL builds, and that isn't a convincing case to keep them.
>
> Why not?
Because it's something we can justifiably replace with a single compile-time
constant, since it's only for low-level debug. I don't see that as a reason
for keeping these machine numbers around if that's all they're used for.
However...
> Kernel infrastructure backward compatibility means that you need to keep
> struct machine_desc instances around. Granted, for the DT case, many of
> the members could be NULL or initialized with dummy stubs. But that is
> very cheap to keep around, and that allows the same kernel binary to be
> able to use both the DT boot and the legacy boot.
... this is a good point; if it helps with the transition, then this is
probably a decent reason to keep it in the interface.
I'd like to keep my "only use the device tree" value (MACH_TYPE_DT =
0xffffffff) though, so we don't needlessly allocate machine numbers where they
aren't actually used.
Cheers,
Jeremy
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