Change in ...coreboot[master]: Documentation/soc/intel: Add MP Initialization document

[Patrick Georgi (Code Review)]

Patrick Georgi has submitted this change and it was merged. ( https://review.coreboot.org/c/coreboot/+/31841 )

Change subject: Documentation/soc/intel: Add MP Initialization document
......................................................................

Documentation/soc/intel: Add MP Initialization document

This patch provides documentation for MP initialization
option available in coreboot.

Change-Id: I055808e2ddf03663e1ec5d3d423054d1caa911cb
Signed-off-by: Subrata Banik 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/31841
Tested-by: build bot (Jenkins) 
Reviewed-by: Patrick Georgi 
---
M Documentation/soc/intel/index.md
A Documentation/soc/intel/mp_init/mp_init.md
2 files changed, 57 insertions(+), 0 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Patrick Georgi: Looks good to me, approved

diff --git a/Documentation/soc/intel/index.md b/Documentation/soc/intel/index.md
index 8a4c297..4f6b4f2 100644
--- a/Documentation/soc/intel/index.md
+++ b/Documentation/soc/intel/index.md
@@ -7,3 +7,4 @@
 - [Common code development strategy](code_development_model/code_development_model.md)
 - [FSP](fsp/index.md)
 - [Ice Lake/9th Gen Core-i series](icelake/index.md)
+- [MP Initialization](mp_init/mp_init.md)
diff --git a/Documentation/soc/intel/mp_init/mp_init.md b/Documentation/soc/intel/mp_init/mp_init.md
new file mode 100644
index 0000000..f81ffc1
--- /dev/null
+++ b/Documentation/soc/intel/mp_init/mp_init.md
@@ -0,0 +1,56 @@
+# Multiple Processor (MP) Initialization
+
+This section is intended to document the purpose of performing multiprocessor
+initialization and its possible ways in coreboot space.
+
+Entire CPU multiprocessor initialization can be divided into two parts
+1. BSP (Boot Strap Processor) Initialization
+2. AP (Application Processor) Initialization
+
+* [Multiple Processor Init](https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-3...) - section 8.4
+
+## Problem Statement
+
+1. coreboot is capable enough to handle multiprocessor initialization on
+IA platforms.
+
+2. With restricted CPU programming logic, there might be some cases where
+certain feature programming can't be open sourced at early development of SOC.
+
+Platform code might need to compromise on those closed source nature of CPU
+programming if we don't plan to provide an alternate interface which can be
+used by coreboot to get rid of such close sourced CPU programming.
+
+## Possible Solution Space
+
+Considering these facts, there are 3 possible solutions to perform MP
+initialization from coreboot + FSP space.
+
+1. coreboot to perform complete MP initialization by its own. This includes
+BSP and AP programming of CPU features mostly non-restricted one. Preferred
+Kconfig is USE_COREBOOT_NATIVE_MP_INIT. SoCs like SKL, KBL, APL are okay to
+make use of same Kconfig option for MP initialization.
+
+2. Alternatively, SoC users also can skip coreboot doing MP initialization
+and make use of FSP binary to perform same task. This can be achieved by using
+Kconfig name USE_INTEL_FSP_MP_INIT. As of 2019 all Google Chrome products are
+using coreboot native MP initialization mechanism and some IOTG platforms
+are using FSP MP Init solution as well.
+
+3. Final option is to let coreboot publish PPI (PEIM to PEIM Interface) to
+perform some restricted (closed source) CPU programming. In that case,
+coreboot will use its native MP init and additionally publish MP service PPI
+for FSP to consume. FSP will execute some CPU programming using same PPI
+service from its own context. One can use
+USE_INTEL_FSP_TO_CALL_COREBOOT_PUBLISH_MP_PPI Kconfig to perform this
+operation.
+
+For latest SoCs like CNL, WHL, ICL, etc, its recommended to make use of this
+option in order to perform SGX and C6DRAM enabling.
+
+Typically all platforms supported by FSP 2.1 specification will have
+external PPI service feature implemented.
+
+[References]
+- [PPI](../fsp/ppi/ppi.md)
+- [MP Service PPI](../fsp/ppi/mp_service_ppi.md)