The top-level xscom nodes specify the mapping range from the 64-bit address space into the PCB address space.
There’s one mapping range per chip xscom, therefore one node per mapping range.
/ /xscom@<chip-base-address-0>/ /xscom@<chip-base-address-1>/ … /xscom@<chip-base-address-n>/
where <chip-base-address-n> is the xscom base address with the gcid-specific bits (for chip n) OR-ed in.
Each xscom node has the following properties:
#address-cells = 1
#size-cells = 1
reg = <base-address[#parent-address-cells] size[#parent-size-cells]>
ibm,chip-id = gcid
compatible = “ibm,xscom”, “ibm,power8-scom” / “ibm,power7-xscom”
ecid = <Electronic Chip ID, applicable for POWER9 onwards>
wafer-id = <wafer ID, applicable for POWER9 onwards>
wafer-location = <wafer location, applicable for POWER9 onwards>
Electronic Chip ID (ECID) is a process by which the wafer number, chip location (i.e. X,Y) and other optional data items are electrically encoded directly on the chip. wafer-id property represents wafer number and wafer-location property represents chip location (both X and Y location).
One sub-node per endpoint. Endpoints are defined by their (port, endpoint-address) data on the PCB, and are named according to their endpoint types:
/xscom@<chip-base-address>/ /xscom@<chip-base-address>/chiptod@<endpoint-addr> /xscom@<chip-base-address>/lpc@<endpoint-addr>
where the <endpoint-addr> is a single address (as distinct from the current (gcid,base) format), consisting of the SCOM port and SCOM endpoint bits in their 31-bit address format.
Each endpoint node has the following properties:
reg = <endpoint-address[#parent-address-cells] size[#parent-size-cells]>
compatible - depends on endpoint type, eg “ibm,power8-chiptod”
The endpoint address specifies the address on the PCB. So, to calculate the MMIO address for a PCB register:
mmio_addr = <xscom-base-addr> | (pcb_addr[1:27] << 4) | (pcb_addr[28:31] << 3)
xscom-base-addr is the address from the first two cells of the parent node’s reg property
pcb_addr is the first cell of the endpoint’s reg property