[OpenPower-Firmware] Questions about SCOM access

[Igor Bagnucki]

Hello,

I'm doing some initial work at 3mdeb for Insurgo, to bring Power9 
(specifically Talos II) support into coreboot and I have some questions 
about SCOM that I can't find an answer for. Reading through documents 
POWER9_Registers_vol1/2/3, I have found only general information about 
SCOM controller. I have also tried to find information in the hostboot 
source code, but the code is quite complicated to understand.

Hostboot configures the hardware using plenty of SCOM registers. How can 
I access these registers?
For example, if I would like to access register PU_OCB_OCI_OCCHBR_SCOM 
which has the SCOM address of 0x6C08F, how would I access this register?

Knowing the initial values of the SCOM registers would be very helpful. 
Are there any documents describing in what state are the registers on 
power-on?

I understand that before accessing registers the SCOM controller has to 
be initialized. Is there some kind of documentation where information 
about this can be found?

--
Igor Bagnucki
Junior Embedded Firmware Developer
https://3mdeb.com | @3mdeb_com