AMD systems have historically provided an "AMD Node ID" that is a unique
identifier for each die in a multi-die package. This was associated with
a unique instance of the AMD Northbridge on a legacy system. And now it
is associated with a unique instance of the AMD Data Fabric on modern
systems. Each instance is referred to as a "Node"; this is an
AMD-specific term not to be confused with NUMA nodes.

The data fabric provides a number of interfaces accessible through a set
of functions in a single PCI device. There is one PCI device per Data
Fabric (AMD Node), and multi-die systems will see multiple such PCI
devices. The AMD Node ID matches a Node's position in the PCI hierarchy.
For example, the Node 0 is accessed using the first PCI device, Node 1
is accessed using the second, and so on. A logical CPU can find its AMD
Node ID using CPUID. Furthermore, the AMD Node ID is used within the
hardware fabric, so it is not purely a logical value.

Heterogeneous AMD systems, with a CPU Data Fabric connected to GPU data
fabrics, follow a similar convention. Each CPU and GPU die has a unique
AMD Node ID value, and each Node ID corresponds to PCI devices in
sequential order.

However, there are two caveats:
1) GPUs are not x86, and they don't have CPUID to read their AMD Node ID
like on CPUs. This means the value is more implicit and based on PCI
enumeration and hardware-specifics.
2) There is a gap in the hardware values for AMD Node IDs. Values 0-7
are for CPUs and values 8-15 are for GPUs.

For example, a system with one CPU die and two GPUs dies will have the
following values:
  CPU0 -> AMD Node 0
  GPU0 -> AMD Node 8
  GPU1 -> AMD Node 9

EDAC is the only subsystem where this has a practical effect. Memory
errors on AMD systems are commonly reported through MCA to a CPU on the
local AMD Node. The error information is passed along to EDAC where the
AMD EDAC modules use the AMD Node ID of reporting logical CPU to access
AMD Node information.

However, memory errors from a GPU die will be reported to the CPU die.
Therefore, the logical CPU's AMD Node ID can't be used since it won't
match the AMD Node ID of the GPU die. The AMD Node ID of the GPU die is
provided as part of the MCA information, and the value will match the
hardware enumeration (e.g. 8-15).

Handle this situation by discovering GPU dies the same way as CPU dies
in the AMD NB code. But do a "node id" fixup in AMD64 EDAC where it's
needed.

The GPU data fabrics provide a register with the base AMD Node ID for
their local "type", i.e. GPU data fabric. This value is the same for all
fabrics of the same type in a system.

Read and cache the base AMD Node ID from one of the GPU devices during
module initialization. Use this to fixup the "node id" when reporting
memory errors at runtime.

  [ bp: Squash a fix making gpu_node_map static as reported by
        Tom Rix <trix@redhat.com>.
    Link: https://lore.kernel.org/r/20230610210930.174074-1-trix@redhat.com ]
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Co-developed-by: Muralidhara M K <muralidhara.mk@amd.com>
Signed-off-by: Muralidhara M K <muralidhara.mk@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230515113537.1052146-6-muralimk@amd.com