Documentation: Add coreboot architecture

Describe the coreboot stages, given a short introduction what is done
and add a chart for coreboot's vs EDK II bootflow as well as the source
for the SVG.

TODO: Describe stages in detail in a separate commit.

Change-Id: I98cb61b1d0d29ac9d03f5ef3644d51a8e14bad74
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32123
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

4 files changed, 282 insertions, 0 deletions

diff --git a/Documentation/getting_started/architecture.md b/Documentation/getting_started/architecture.md
new file mode 100644
index 000000000000..6ef63594cf1c
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+++ b/Documentation/getting_started/architecture.md
@@ -0,0 +1,105 @@
+# coreboot architecture
+
+## Overwiew
+![][architecture]
+
+[architecture]: comparision_coreboot_uefi.svg
+
+## Stages
+coreboot consists of multiple stages that are compiled as separate binaries and
+are inserted into the CBFS with custom compression. The bootblock usually doesn't
+have compression while the ramstage and payload are compressed with LZMA.
+
+Each stage loads the next stage a given address (possibly decompressing it).
+
+Some stages are relocatable and can be placed anywhere in DRAM. Those stages are
+usually cached in CBMEM for faster loading times on ACPI S3 resume.
+
+Supported stage compressions:
+* none
+* LZ4
+* LZMA
+
+## bootblock
+The bootblock is the first stage executed after CPU reset. It is written in
+assembly language and its main task is to set up everything for a C-environment:
+
+Common tasks:
+
+* Cache-As-RAM for heap and stack
+* Set stack pointer
+* Clear memory for BSS
+* Decompress and load the next stage
+
+On x86 platforms that includes:
+
+* Microcode updates
+* Timer init
+* Switching from 16-bit real-mode to 32-bit protected mode
+
+The bootblock loads the romstage or the verstage if verified boot is enabled.
+
+### Cache-As-Ram
+The *Cache-As-Ram*, also called Non-Eviction mode, or *CAR* allows to use the
+CPU cache like regular SRAM. This is particullary usefull for high level
+languages like `C`, which need RAM for heap and stack.
+
+The CAR needs to be activated using vendor specific CPU instructions.
+
+The following stages run when Cache-As-Ram is active:
+* bootblock
+* romstage
+* verstage
+* postcar
+
+## verstage
+The verstage is where the root-of-trust starts. It's assumed that
+it cannot be overwritten in-field (together with the public key) and
+it starts at the very beginning of the boot process.
+The verstage installs a hook to verify a file before it's loaded from
+CBFS or a partition before it's accessed.
+
+The verified boot mechanism allows trusted in-field firmware updates
+combined with a fail-safe recovery mode.
+
+## romstage
+The romstage initializes the DRAM and prepares everything for device init.
+
+Common tasks:
+
+* Early device init
+* DRAM init
+
+## postcar
+To leave the CAR setup and run code from regular DRAM the postcar-stage tears
+down CAR and loads the ramstage. Compared to other stages it's minimal in size.
+
+## ramstage
+
+The ramstage does the main device init:
+
+* PCI device init
+* On-chip device init
+* TPM init (if not done by verstage)
+* Graphics init (optional)
+* CPU init (like set up SMM)
+
+After initialization tables are written to inform the payload or operating system
+about the current hardware existance and state. That includes:
+
+* ACPI tables (x86 specific)
+* SMBIOS tables (x86 specific)
+* coreboot tables
+* devicetree updates (ARM specific)
+
+It also does hardware and firmware lockdown:
+* Write-protection of boot media
+* Lock security related registers
+* Lock SMM mode (x86 specific)
+
+## payload
+The payload is the software that is run after coreboot is done. It resides in
+the CBFS and there's no possibility to choose it at runtime.
+
+For more details have a look at [payloads](../payloads.md).
+
diff --git a/Documentation/getting_started/comparision_coreboot_uefi.dia b/Documentation/getting_started/comparision_coreboot_uefi.dia
new file mode 100644
index 000000000000..19c491fa7e66
--- /dev/null
+++ b/Documentation/getting_started/comparision_coreboot_uefi.dia
diff --git a/Documentation/getting_started/comparision_coreboot_uefi.svg b/Documentation/getting_started/comparision_coreboot_uefi.svg
new file mode 100644
index 000000000000..3ea2fa69300d
--- /dev/null
+++ b/Documentation/getting_started/comparision_coreboot_uefi.svg
@@ -0,0 +1,176 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN" "http://www.w3.org/TR/2001/PR-SVG-20010719/DTD/svg10.dtd">
+<svg width="55cm" height="28cm" viewBox="62 37 1088 559" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+  <g>
+    <rect style="fill: #ffffff" x="63.296" y="74.0258" width="1085.8" height="520.893"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 2; stroke: #ffffff" x="63.296" y="74.0258" width="1085.8" height="520.893"/>
+  </g>
+  <line style="fill: none; fill-opacity:0; stroke-width: 4; stroke: #000000" x1="242.613" y1="107.463" x2="242.698" y2="492.591"/>
+  <g>
+    <line style="fill: none; fill-opacity:0; stroke-width: 4; stroke: #000000" x1="234.964" y1="477.053" x2="1135.15" y2="478.109"/>
+    <polyline style="fill: none; fill-opacity:0; stroke-width: 4; stroke: #000000" points="1124.61,485.597 1139.62,478.114 1124.63,470.597 "/>
+  </g>
+  <text font-size="22.5778" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="482.342" y="58.1574">
+    <tspan x="482.342" y="58.1574">Platform Initialization Firmware Phases</tspan>
+  </text>
+  <text font-size="16.9333" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="98.4514" y="435.714">
+    <tspan x="98.4514" y="435.714">EDK II - stages</tspan>
+  </text>
+  <text font-size="12.8" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="1073.49" y="499.998">
+    <tspan x="1073.49" y="499.998">time</tspan>
+  </text>
+  <text font-size="16.9333" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="82.8266" y="330.476">
+    <tspan x="82.8266" y="330.476">coreboot - stages</tspan>
+  </text>
+  <g>
+    <rect style="fill: #faff94" x="250.501" y="404.247" width="130.432" height="69.1471"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="250.501" y="404.247" width="130.432" height="69.1471"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="315.718" y="434.72">
+      <tspan x="315.718" y="434.72">Security</tspan>
+      <tspan x="315.718" y="450.72">(SEC)</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #faff94" x="383.033" y="404.781" width="282.702" height="69"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="383.033" y="404.781" width="282.702" height="69"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="524.384" y="427.181">
+      <tspan x="524.384" y="427.181">Pre-EFI</tspan>
+      <tspan x="524.384" y="443.181">Initialization Environment</tspan>
+      <tspan x="524.384" y="459.181">(PEI)</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #faff94" x="668.027" y="405.317" width="269.244" height="69"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="668.027" y="405.317" width="269.244" height="69"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="802.649" y="427.717">
+      <tspan x="802.649" y="427.717">Driver Execution</tspan>
+      <tspan x="802.649" y="443.717">Environment</tspan>
+      <tspan x="802.649" y="459.717">(DXE)</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #faff94" x="939.541" y="405.727" width="178.75" height="69"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="939.541" y="405.727" width="178.75" height="69"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="1028.92" y="436.127">
+      <tspan x="1028.92" y="436.127">Boot Device Selection</tspan>
+      <tspan x="1028.92" y="452.127">(BDS)</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #90c9ff" x="254.747" y="291.309" width="125.314" height="69.1471"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="254.747" y="291.309" width="125.314" height="69.1471"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="317.404" y="329.782">
+      <tspan x="317.404" y="329.782">bootblock</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #90c9ff" x="476.354" y="290.735" width="89.65" height="69.1471"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="476.354" y="290.735" width="89.65" height="69.1471"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="521.179" y="329.209">
+      <tspan x="521.179" y="329.209">romstage</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #90c9ff" x="382.317" y="291.011" width="92.1" height="69.1471"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="382.317" y="291.011" width="92.1" height="69.1471"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="428.367" y="321.485">
+      <tspan x="428.367" y="321.485">verstage</tspan>
+      <tspan x="428.367" y="337.485">(optional)</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #90c9ff" x="567.853" y="290.99" width="98.5152" height="69.1471"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="567.853" y="290.99" width="98.5152" height="69.1471"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="617.11" y="321.464">
+      <tspan x="617.11" y="321.464">postcar</tspan>
+      <tspan x="617.11" y="337.464">(x86 only)</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #90c9ff" x="667.529" y="281.527" width="168.747" height="37"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="667.529" y="281.527" width="168.747" height="37"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="751.903" y="303.927">
+      <tspan x="751.903" y="303.927">ramstage</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #90c9ff" x="667.84" y="321.487" width="167.519" height="53"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="667.84" y="321.487" width="167.519" height="53"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="751.6" y="343.887">
+      <tspan x="751.6" y="343.887">SMM</tspan>
+      <tspan x="751.6" y="359.887">(x86 only)</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #90c9ff" x="941.841" y="283.151" width="171.98" height="69.1471"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="941.841" y="283.151" width="171.98" height="69.1471"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="1027.83" y="321.624">
+      <tspan x="1027.83" y="321.624">payload</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #d8e5e5" x="253.112" y="209.178" width="82.7" height="27"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="253.112" y="209.178" width="82.7" height="27"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="294.462" y="226.578">
+      <tspan x="294.462" y="226.578">Assembly</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #00c800" x="318.155" y="129.267" width="283.43" height="27"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="318.155" y="129.267" width="283.43" height="27"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="459.87" y="146.667">
+      <tspan x="459.87" y="146.667">Cache-As-RAM</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #ff8484" x="506.676" y="159.67" width="599.421" height="27"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="506.676" y="159.67" width="599.421" height="27"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="806.387" y="177.07">
+      <tspan x="806.387" y="177.07">DRAM</tspan>
+    </text>
+  </g>
+  <line style="fill: none; fill-opacity:0; stroke-width: 1; stroke-dasharray: 4; stroke: #000000" x1="175.046" y1="392.926" x2="1113.82" y2="391.893"/>
+  <text font-size="12.7998" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="387.045" y="241.637">
+    <tspan x="387.045" y="241.637"></tspan>
+  </text>
+  <g>
+    <rect style="fill: #ffffff" x="337.438" y="209.383" width="618.831" height="27"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="337.438" y="209.383" width="618.831" height="27"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="646.853" y="226.783">
+      <tspan x="646.853" y="226.783">C</tspan>
+    </text>
+  </g>
+  <g>
+    <rect style="fill: #f6c7c7" x="667.35" y="238.912" width="170.3" height="27"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="667.35" y="238.912" width="170.3" height="27"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="752.5" y="256.312">
+      <tspan x="752.5" y="256.312">ADA SPARK (x86 only)</tspan>
+    </text>
+  </g>
+  <text font-size="16.9333" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="84.2481" y="233.28">
+    <tspan x="84.2481" y="233.28">coreboot</tspan>
+    <tspan x="84.2481" y="254.446">source languages</tspan>
+  </text>
+  <text font-size="16.9333" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="86.5008" y="153.786">
+    <tspan x="86.5008" y="153.786">code/heap</tspan>
+    <tspan x="86.5008" y="174.953">memory location </tspan>
+  </text>
+  <line style="fill: none; fill-opacity:0; stroke-width: 1; stroke-dasharray: 4; stroke: #000000" x1="175.483" y1="273.35" x2="1109.07" y2="273.582"/>
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+    <rect style="fill: #90c9ff" x="838.583" y="281.963" width="100.3" height="53"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="838.583" y="281.963" width="100.3" height="53"/>
+    <text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="888.733" y="304.363">
+      <tspan x="888.733" y="304.363">BL31</tspan>
+      <tspan x="888.733" y="320.363">(ARM only)</tspan>
+    </text>
+  </g>
+  <text font-size="12.7998" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="209.772" y="508.772">
+    <tspan x="209.772" y="508.772">Power on</tspan>
+  </text>
+  <g>
+    <rect style="fill: #ffffff" x="941.939" y="210.26" width="22.4641" height="25.1384"/>
+    <rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #ffffff" x="941.939" y="210.26" width="22.4641" height="25.1384"/>
+  </g>
+  <path style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" d="M 955.029 209.941 C 967.678,210.1 946.349,230.772 955.598,237.021"/>
+</svg>
diff --git a/Documentation/getting_started/index.md b/Documentation/getting_started/index.md
index 8f2a58e1c5ff..52d873ece2bf 100644
--- a/Documentation/getting_started/index.md
+++ b/Documentation/getting_started/index.md
@@ -1,5 +1,6 @@
 # Getting Started
 
+* [coreboot architecture](architecture.md)
 * [Build System](build_system.md)
 * [Submodules](submodules.md)
 * [Kconfig](kconfig.md)