Introduce the ARM TF reset design document

This patch introduces a new document presenting the ARM Trusted
Firmware Reset Design. It shows the reset code flow, lists the
different build options that affect it, in which case to use them
and what their exact effect is.

The section about using BL31 entrypoint as the reset address has
been moved from the general firmware design document to this one.
It's also been improved to explain why the FVP port supports the
RESET_TO_BL31 configuration, even though the reset vector address
can't be programmed dynamically.

This document includes some images, which have been generated using
Dia version 0.97.2. This tool can be obtained from:
https://wiki.gnome.org/Apps/Dia/Download
This patch provides:
 - the image files describing the different reset flow diagrams;
 - the source '.dia' file;
 - a script automating the generation of the images from the '.dia'
   file.
Note that the 2 latter files are not actually needed for the document
and are provided for convenience only, in case the reset images need
to be modified.

Change-Id: Ib6302e8209d418a5b31c4e85e55fd9e83caf2ca2

6 files changed, 41 insertions, 0 deletions

diff --git a/docs/diagrams/default_reset_code.png b/docs/diagrams/default_reset_code.png
new file mode 100644
index 00000000..e7e0d855
--- /dev/null
+++ b/docs/diagrams/default_reset_code.png
diff --git a/docs/diagrams/generate_reset_images.sh b/docs/diagrams/generate_reset_images.sh
new file mode 100755
index 00000000..eef5648d
--- /dev/null
+++ b/docs/diagrams/generate_reset_images.sh
@@ -0,0 +1,41 @@
+#! /bin/bash
+
+#
+# This script generates the image files used in the ARM Trusted Firmware Reset
+# Design document from the 'reset_code_flow.dia' file.
+#
+# The PNG files in the present directory have been generated using Dia version
+# 0.97.2, which can be obtained from https://wiki.gnome.org/Apps/Dia/Download
+#
+
+set -e
+
+# Usage: generate_image <layers> <image_filename>
+function generate_image
+{
+	dia				\
+		--show-layers=$1	\
+		--filter=png		\
+		--export=$2		\
+		reset_code_flow.dia
+
+}
+
+# The 'reset_code_flow.dia' file is organized in several layers.
+# Each image is generated by combining and exporting the appropriate set of
+# layers.
+generate_image								\
+	Frontground,Background,cpu_type_check,boot_type_check		\
+	default_reset_code.png
+
+generate_image								\
+	Frontground,Background,no_cpu_type_check,boot_type_check	\
+	reset_code_no_cpu_check.png
+
+generate_image								\
+	Frontground,Background,cpu_type_check,no_boot_type_check	\
+	reset_code_no_boot_type_check.png
+
+generate_image								\
+	Frontground,Background,no_cpu_type_check,no_boot_type_check	\
+	reset_code_no_checks.png
diff --git a/docs/diagrams/reset_code_flow.dia b/docs/diagrams/reset_code_flow.dia
new file mode 100644
index 00000000..5de00dad
--- /dev/null
+++ b/docs/diagrams/reset_code_flow.dia
diff --git a/docs/diagrams/reset_code_no_boot_type_check.png b/docs/diagrams/reset_code_no_boot_type_check.png
new file mode 100644
index 00000000..8ce7e97a
--- /dev/null
+++ b/docs/diagrams/reset_code_no_boot_type_check.png
diff --git a/docs/diagrams/reset_code_no_checks.png b/docs/diagrams/reset_code_no_checks.png
new file mode 100644
index 00000000..8a02f0f8
--- /dev/null
+++ b/docs/diagrams/reset_code_no_checks.png
diff --git a/docs/diagrams/reset_code_no_cpu_check.png b/docs/diagrams/reset_code_no_cpu_check.png
new file mode 100644
index 00000000..8b05ea4d
--- /dev/null
+++ b/docs/diagrams/reset_code_no_cpu_check.png