chapter3: recommend smccc >= 1.1

This is to encourage implementing the `SMCCC_VERSION' function, which eases discovery. Suggested-by: Etienne Carrière <[email protected]> Signed-off-by: Vincent Stehlé <[email protected]>
ARM-software · Feb 27, 2024 · c92bdca · c92bdca
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diff --git a/source/chapter3-secureworld.rst b/source/chapter3-secureworld.rst
@@ -17,25 +17,31 @@ At `ExitBootServices()` time, all secondary CPUs must be parked or powered off.
 AArch64 Multiprocessor Startup Protocol
 =======================================
 On AArch64 platforms, Firmware resident in Trustzone EL3 must implement and
-conform to the Power State Coordination Interface specification [PSCI]_.
+conform to the Power State Coordination Interface specification [PSCI]_ and to
+the SMC Calling Convention [SMCCC]_.
 
 Platforms without EL3 must implement one of:
 
-- PSCI at EL2 (leaving only EL1 available to an operating system)
+- PSCI and SMCCC at EL2 (leaving only EL1 available to an operating system)
 - Linux AArch64 spin tables [LINUXA64BOOT]_ (Devicetree only)
 
 However, the spin table protocol is strongly discouraged.
-Future versions of this specification will only allow PSCI, and PSCI should
-be implemented in all new designs.
+Future versions of this specification will only allow PSCI and SMCCC, and they
+should be implemented in all new designs.
 
-It is recommended that firmware implementing PSCI supports version 1.0 or later.
-[#PSCINote]_
+It is recommended that firmware implementing PSCI supports version 1.0 or later
+[#PSCINote]_ and that firmware implementing SMCCC supports version 1.1 or later
+[#SMCCCNote]_.
 
 .. [#PSCINote]
    PSCI version 1.0 is considered as an errata fix release for version 0.2,
    where functions interfaces have been stabilized.
    It also introduced the `PSCI_FEATURES` function, for standardized discovery.
 
+.. [#SMCCCNote]
+   Starting with SMCCC version 1.1, support for the `SMCCC_VERSION` function is
+   required, for standardized discovery.
+
 RISC-V Multiprocessor Startup Protocol
 ======================================
 The resident firmware in M mode or hypervisor running in HS mode must implement

diff --git a/source/references.rst b/source/references.rst
@@ -22,6 +22,10 @@
    <https://developer.arm.com/documentation/den0022/f>`_
    July 2023, `Arm Limited <https://www.arm.com/>`_
 
+.. [SMCCC] `SMC Calling Convention version F.
+   <https://developer.arm.com/documentation/den0028/f>`_
+   Dec 2023, `Arm Limited <https://www.arm.com/>`_
+
 .. [ArmBBR] `Arm Base Boot Requirements specification Issue G (v2.0)
    <https://developer.arm.com/documentation/den0044/g>`_
    15 Apr 2022, `Arm Limited <https://www.arm.com/>`_