Subrata Banik has uploaded this change for review.
Documentation/Intel: Add MultiProcessorInit documentation
Add documentation for MP service PPI using EFI interface
on Intel 9th Gen Platforms.
Documented so far:
* Problem Statement
* New Design Proposal
* API interface
* Code Flow changes
* Benefits
BRANCH=none
BUG=b:74436746
TEST=none
Change-Id: I5b6096ef31d8a523c00cbad39ab9d4884e735fde
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
---
A Documentation/Intel/MultiProcessorInit/Coreboot_Publish_MP_Service_API.png
A Documentation/Intel/MultiProcessorInit/MultiProcessorInit.md
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diff --git a/Documentation/Intel/MultiProcessorInit/MultiProcessorInit.md b/Documentation/Intel/MultiProcessorInit/MultiProcessorInit.md
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+# Intel Common Code Block Publishing EFI_MP_SERVICES_PPI
+
+## Introduction
+
+This documentation is intended to document the purpose for creating EFI service
+Interface inside Coreboot space to perform CPU feature programming on Application
+Processors for Intel 9th Gen (Cannon Lake) and beyond CPUs.
+
+Today Coreboot is capable enough to handle multi-processor initialization on IA platforms.
+
+The multi-processor initialization code has to take care of lots of duties:
+
+1 Bringing all cores out of reset
+2 Load latest microcode on all cores
+3 Sync latest MTRR snapshot between BSP and APs
+4 Perform sets of CPU feature programming
+ * CPU Power & Thermal Management
+ * Overclocking
+ * Intel Trusted Execution Technology
+ * Intel Software Guard Extensions
+ * Intel Processor Trace etc.
+
+This above CPU feature programming lists are expected to grow with current and future
+CPU complexity and there might be some cases where certain feature programming mightbe
+closed source in nature.
+
+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 source CPU programming.
+
+## Proposal
+
+As Coreboot is doing CPU multi-processor initialization for IA platform before FSP-S
+initialization and having all possible information about cores in terms of maximum number
+of cores, APIC ids, stack size etc. It’s also possible for Coreboot to extend its own
+support model and create a sets of APIs which later can be used by FSP to run CPU feature
+programming using Coreboot published APIs.
+
+Due to the fact that FSP is using EFI infrastructure and need to relying on install/locate
+PPI to perform certain API call, hence Coreboot has to created MP services APIs known as
+EFI_MP_SERVICES_PPI as per PI specification volume 1, section 8.3.9.
+More details here: http://www.uefi.org/sites/default/files/resources/PI_Spec_1_6.pdf
+
+### Coreboot to publish EFI_MP_SERVICES_PPI APIs
+| API | Description |
+|------------------------------|------------------------------------------------------------------|
+| PeiGetNumberOfProcessors | Get the number of CPU's. |
+| PeiGetProcessorInfo | Get information on a specific CPU. |
+| PeiStartupAllAPs | Activate all of the application processors. |
+| PeiStartupThisAP | Activate a specific application processor. |
+| PeiSwitchBSP | Switch the boot strap processor. |
+| PeiEnableDisableAP | Enable or disable an application processor. |
+| PeiWhoAmI | Identify the currently executing processor. |
+|------------------------------|------------------------------------------------------------------|
+
+
+## Code Flow
+
+Here is proposed design flow with Coreboot has implemented EFI_MP_SERVICES_PPI API and FSP will make
+use of the same to perform some CPU feature programming.
+
+** Coreboot-FSP MP init flow **
+![alt text][Coreboot_Publish_MP_Service_API]
+
+[Coreboot_Publish_MP_Service_API]: Coreboot_Publish_MP_Service_API.png "Coreboot-FSP MP init flow"
+
+## Benefits
+1. Coreboot was using SkipMpInit=1 which will skip entire FSP CPU feature programming.
+With proposed model, Coreboot will make use of SkipMpInit=0 which will allow to run all
+Silicon recommended CPU programming.
+2. CPU feature programming inside FSP will be more transparent than before as it’s using
+Coreboot interfaces to execute those programming.
+3. Coreboot will have more control over running those feature programming as API optimization
+handled by Coreboot.
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