[PATCH] docs: fusa: Add Assumption of Use (AOU)

[Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>]

From: Michal Orzel <michal.orzel@xxxxxxx>

AOU are the assumptions Xen relies on other components (eg platform, domains)
to fulfill its requirements. In our case, platform means a combination of
hardware, firmware and bootloader.

We have defined AOU in the intro.rst and added AOU for the generic timer.

Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
---
 .../reqs/design-reqs/arm64/generic-timer.rst  | 19 +++++++++++++++++++
 docs/fusa/reqs/intro.rst                      | 10 ++++++++++
 2 files changed, 29 insertions(+)

diff --git a/docs/fusa/reqs/design-reqs/arm64/generic-timer.rst 
b/docs/fusa/reqs/design-reqs/arm64/generic-timer.rst
index f2a0cd7fb8..9df87cf4e0 100644
--- a/docs/fusa/reqs/design-reqs/arm64/generic-timer.rst
+++ b/docs/fusa/reqs/design-reqs/arm64/generic-timer.rst
@@ -116,6 +116,25 @@ Rationale:
 
 Comments:
 
+Covers:
+ - `XenProd~emulated_timer~1`
+
+Assumption of Use on the Platform
+=================================
+
+Expose system timer frequency via register
+------------------------------------------
+
+`XenSwdgn~arm64_generic_timer_pf_program_cntfrq_el0~1`
+
+Description:
+Underlying platform shall ensure that CNTFRQ_EL0 register contains the system
+timer frequency.
+
+Rationale:
+
+Comments:
+
 Covers:
  - `XenProd~emulated_timer~1`
 
diff --git a/docs/fusa/reqs/intro.rst b/docs/fusa/reqs/intro.rst
index 245a219ff2..aa85ff821c 100644
--- a/docs/fusa/reqs/intro.rst
+++ b/docs/fusa/reqs/intro.rst
@@ -38,6 +38,16 @@ The requirements are linked using OpenFastTrace
 OpenFastTrace parses through the requirements and generates a traceability
 report.
 
+Assumption of Use
+=================
+
+To fulfill one or more design requirements, there may be underlying assumptions
+on one or more components that Xen interacts with directly or indirectly. For
+eg, there may be assumptions on the underlying platform (hardware + firmware +
+bootloader) to set certain registers, etc. The important thing here is that
+anyone who validates these requirements, need to consider the assumption on the
+other components.
+
 The following is the skeleton for a requirement.
 
 Title of the requirement
-- 
2.25.1