The SGI Altix PROM supports a SAL call for performance monitoring and for
exporting NUMA topology. We need this in community kernels for diagnostic
and performance tools to use, especially on very large machines.

This patch registers a dynamic misc device "sn_hwperf" that supports an
ioctl interface for reading/writing memory mapped registers on Altix
nodes and routers via the new SAL call. It also creates a read-only
procfs file "/proc/sgi_sn/sn_topology" to export NUMA topology and Altix
hardware inventory.

> What tools are using this?
 
Performance Co-Pilot http://oss.sgi.com/projects/pcp  in particular,
pmshub, shubstats and linkstat. Numerous other users include anything
that needs knowledge of numa topology/interconnect in order to perform
well, e.g. mpt. BTW I have not exported any API functions .. at this
point I don't think we need any modules to call the API.
Signed-off-by: Mark Goodwin <markgw@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>