Scan all buses for CSR bus, not stopping on the first failed
match. Scan all slots for function 0 on the found bus, for instance on
IvyBridge the slot 0 is not decoded at all. Since the scan is quite
unsafe, and access to the buses is mostly useful for developers,
enable the csr buses scan with the tunable.
Current qpi.c makes too many assumptions about the uncore
configuration buses location and about slots occupied. Also it
restricts itself only to Nehalem CPUs. It is needed on all Core-based
Xeons. On the 2600 v2 (IvyBridge) machine I have access to, the CSR
buses have numbers 31 (BSP socket) and 63 (second socket), and there
is no functions pci0.31.0.0 or pci0.63.0.0. According to the CPU
datasheet, all devices on the uncore bus occupy slots >= 8.
Practically, the attach to config buses is required for the intel-pcm
pcm-memory.x tool to work, for instance.
Reviewed by: jhb (previous version)
Sponsored by: Mellanox Technologies
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D12268
3c700e2e4c