SDEI: Update doc to clarify delegation

The explicit event dispatch sequence currently depicts handling done in
Secure EL1, although further error handling is typically done inside a
Secure Partition. Clarify the sequence diagram to that effect.

Change-Id: I53deedc6d5ee0706626890067950c2c541a62c78
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

docs/plantuml/sdei_explicit_dispatch.puml

@@ -9,7 +9,7 @@
 autonumber "<b>[#]</b>"
 participant "SDEI client" as EL2
 participant EL3
-participant SEL1
+participant "Secure Partition" as SP
 
 activate EL2
 EL2->EL3: **SDEI_EVENT_REGISTER**(ev, handler, ...)
@@ -24,11 +24,11 @@ EL3->EL2: 1
 EL3<--]: **CRITICAL EVENT**
 activate EL3 #red
 note over EL3: Critical event triage
-EL3->SEL1: dispatch
+EL3->SP: dispatch
-activate SEL1 #salmon
+activate SP #salmon
-note over SEL1: Critical event handling
+note over SP: Critical event handling
-SEL1->EL3: done
+SP->EL3: done
-deactivate SEL1
+deactivate SP
 EL3-->EL3: sdei_dispatch_event(ev)
 note over EL3: Prepare SDEI dispatch
 EL3->EL2: dispatch

docs/sdei.rst

@@ -232,13 +232,20 @@ bound or dynamic events can't be explicitly dispatched (see the section below).
 
 At a later point in time, a critical event [#critical-event]_ is trapped into
 EL3 [7]. EL3 performs a first-level triage of the event, and decides to dispatch
-to Secure EL1 for further handling [8]. The dispatch completes, but intends to
+to a Secure Partition [#secpart]_ for further handling [8]. The dispatch
-involve Non-secure world in further handling, and therefore decides to
+completes, but intends to involve Non-secure world in further handling, and
-explicitly dispatch an event [10] (which the client had already registered for
+therefore decides to explicitly dispatch an event [10] (which the client had
-[1]). The rest of the sequence is similar to that in the `general SDEI
+already registered for [1]). The rest of the sequence is similar to that in the
-dispatch`_: the requested event is dispatched to the client (assuming all the
+`general SDEI dispatch`_: the requested event is dispatched to the client
-conditions are met), and when the handler completes, the preempted execution
+(assuming all the conditions are met), and when the handler completes, the
-resumes.
+preempted execution resumes.
+
+.. [#critical-event] Examples of critical event are *SError*, *Synchronous
+                     External Abort*, *Fault Handling interrupt*, or *Error
+                     Recovery interrupt* from one of RAS nodes in the system.
+
+.. [#secpart] Dispatching to Secure Partition involves *Secure Partition
+              Manager*, which isn't depicted in the sequence.
 
 Conditions for event dispatch
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -295,10 +302,6 @@ dispatcher:
    context is resumed (as indicated by the ``preempted_sec_state`` parameter of
    the API).
 
-.. [#critical-event] Examples of critical event are *SError*, *Synchronous
-                     External Abort*, *Fault Handling interrupt*, or *Error
-                     Recovery interrupt* from one of RAS nodes in the system.
-
 Porting requirements
 --------------------