lchan and assignment FSMs: make Channel Mode Modify more sane

The Channel Mode Modify procedure is currently implemented for changing
a TCH lchan from signalling to voice mode. For that, however, it is
re-using (abusing) the channel activation structs and state transitions,
and thus always implies activating a voice stream when the mode
modification is done.

I will add a Channel Mode Modify to enable VAMOS mode soon, so I require
separate structs and state transitions which also work on an lchan that
already has a voice stream established: a struct lchan_modify_info and
LCHAN_EV_REQUEST_MODE_MODIFY, and dedicated assignment FSM state
ASSIGNMENT_ST_WAIT_LCHAN_MODIFIED.

For the part where a Channel Mode Modify enables a voice stream after
switching from signalling to speech mode, still use the channel
activation code path, but only once the mode modification is done.

General improvements:
- To ask for a mode modification, emit an FSM event that ensures a mode
  modify only happens when the lchan state allows it.
- The new lchan_modify_info struct reflects only those parts that have
  an effect during a mode modification (before the lchan_activate_info
  was fully populated, many values not having an effect).
- More accurate logging, indicating "Mode Modify" instead of "Channel
  Activation"

A TTCN3 test for the Channel Mode Modify procedure is added in
Idf4efaed986de0bbd2b663313e837352cc139f0f, and the test passes both
before and after this patch is applied.

Related: SYS#4895
Change-Id: I4986844f839b1c9672c61d916eb3d33d0042d747

1 files changed, 8 insertions, 2 deletions

diff --git a/doc/assignment-fsm.dot b/doc/assignment-fsm.dot
index c2181535b..4eb8d9805 100644
--- a/doc/assignment-fsm.dot
+++ b/doc/assignment-fsm.dot
@@ -12,6 +12,7 @@ labelloc=t; label="Assignment FSM"
 	gscon2 [label="conn FSM",shape=box3d]
 	lchan [label="lchan FSM\n(new lchan)",shape=box3d]
 	old_lchan [label="old lchan",shape=box3d]
+	lchan2 [label="lchan FSM",shape=box3d]
 
 	bssap [label="osmo_bsc_bssap.c",shape=box]
 
@@ -22,8 +23,7 @@ labelloc=t; label="Assignment FSM"
 	bssap -> gscon [label="GSCON_EV_ASSIGNMENT_START\ndata=struct assignment_request",style=dotted]
 
 	gscon -> WAIT_LCHAN_ACTIVE [label="assignment_fsm_start()",style=dotted]
-	gscon -> WAIT_LCHAN_ESTABLISHED [label="assignment_fsm_start()\n(mode modify)",style=dotted]
-        WAIT_LCHAN_ACTIVE -> lchan [label="lchan_activate()\nFOR_ASSIGNMENT",style=dotted]
+	WAIT_LCHAN_ACTIVE -> lchan [label="lchan_activate()\nFOR_ASSIGNMENT",style=dotted]
 	lchan -> WAIT_LCHAN_ACTIVE [label="ASSIGNMENT_EV_\nLCHAN_\nACTIVE,ERROR",style=dotted]
 	lchan -> WAIT_LCHAN_ESTABLISHED [label="ASSIGNMENT_EV_\nLCHAN_\nESTABLISHED,ERROR",style=dotted]
 
@@ -40,4 +40,10 @@ labelloc=t; label="Assignment FSM"
 	WAIT_MGW_ENDPOINT_TO_MSC -> gscon2 [label="gscon_connect_\nmgw_to_msc()",style=dotted]
 	gscon2 -> WAIT_MGW_ENDPOINT_TO_MSC [label="ASSIGNMENT_EV_\nMSC_MGW_OK",style=dotted]
 	terminate -> gscon2 [label="GSCON_EV_\nASSIGNMENT_END",style=dotted]
+
+	WAIT_LCHAN_ACTIVE -> WAIT_LCHAN_MODIFIED [label="assignment_fsm_start()\n(mode modify)"]
+	WAIT_LCHAN_MODIFIED -> lchan2 [label="lchan_mode_modify()\nMODIFY_FOR_ASSIGNMENT",style=dotted]
+	lchan2 -> WAIT_LCHAN_MODIFIED [label="ASSIGNMENT_EV_\nLCHAN_\nMODIFIED,ERROR",style=dotted]
+	WAIT_LCHAN_MODIFIED -> WAIT_MGW_ENDPOINT_TO_MSC [label="needs\nvoice\nstream"]
+	WAIT_LCHAN_MODIFIED -> terminate [label="no change\nin voice\nstream"]
 }