chapter3: require FF-A compatible with v1.2

On AArch64, when FF-A is implemented, require compatibility with FF-A v1.2.

Suggested-by: Achin Gupta <achin.gupta@arm.com>
Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>

Author: vstehle

source/chapter3-secureworld.rst

@@ -35,6 +35,20 @@ It is recommended that firmware implements PSCI version 1.0 or later
 .. [#SMCCCNote] Starting with SMCCC version 1.1, support for the `SMCCC_VERSION`
    function is required, for standardized discovery.
 
+AArch64 Firmware Framework
+==========================
+
+On AArch64 platforms, when privileged or secure firmware implements the Firmware
+Framework for A-profile (FF-A), it must conform to the Arm Firmware Framework
+for Arm A-profile specification [FFA]_ and it must support at least one callee
+version compatible with caller version 1.2. [#FFANote]_
+
+.. [#FFANote] FF-A v1.2 introduced support for multiple services UUIDs in a
+   partition, which eases services discovery, as well as the supporting
+   `FFA_MSG_SEND_DIRECT_REQ2` ABI.
+   As per the FF-A specification § 13.2.1 Overview, all callee versions 1.x,
+   with x >= 2, are compatible with caller version 1.2.
+
 RISC-V Multiprocessor Startup Protocol
 ======================================