lchan_fsm: make rsl mode-modify working again

osmo-nitb supports the modification of an lchan if the lchan is
compatible but in the wrong mode. This feature was dropped in the
transition to AoIP/bsc-split. However, osmo-bsc still has code to
generate and parse the messeages, but the FSMs do not support a mode
modify yetm

Lets add handling for mode-modify to the lchan_fsm and assignment_fsm in
order to support mode modify again

Change-Id: I2c5a283b1ee33745cc1fcfcc09a0f9382224e2eb
Related: OS#4549

4 files changed, 35 insertions, 0 deletions

diff --git a/doc/assignment-fsm.dot b/doc/assignment-fsm.dot
index 5a3a2b91f..c2181535b 100644
--- a/doc/assignment-fsm.dot
+++ b/doc/assignment-fsm.dot
@@ -22,6 +22,7 @@ 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]
 	lchan -> WAIT_LCHAN_ACTIVE [label="ASSIGNMENT_EV_\nLCHAN_\nACTIVE,ERROR",style=dotted]
 	lchan -> WAIT_LCHAN_ESTABLISHED [label="ASSIGNMENT_EV_\nLCHAN_\nESTABLISHED,ERROR",style=dotted]
diff --git a/doc/assignment.msc b/doc/assignment.msc
index 4e690a811..fae088f23 100644
--- a/doc/assignment.msc
+++ b/doc/assignment.msc
@@ -9,6 +9,14 @@ msc {
 	gscon note gscon [label="GSCON_EV_ASSIGNMENT_START\n data=struct assignment_request"];
 	gscon abox gscon [label="ST_ASSIGNMENT"];
 	ass <- gscon [label="assignment_fsm_start()"];
+	|||;
+	--- [label="IF current lchan supports requested channel mode (re-use)"];
+	lchan <- ass [label="LCHAN_EV_REQUEST_MODE_MODIFY"];
+	ass abox ass [label="ASSIGNMENT_ST_\nWAIT_LCHAN_ESTABLISHED"];
+	ass rbox ass [label="see below"];
+
+	|||;
+	--- [label="ELSE: if current lchan does not support requested channel mode (establish new lchan)"];
 	ass abox ass [label="ASSIGNMENT_ST_\nWAIT_LCHAN_ACTIVE"];
 
 	|||;
diff --git a/doc/lchan-fsm.dot b/doc/lchan-fsm.dot
index b726b0c87..fe35903f7 100644
--- a/doc/lchan-fsm.dot
+++ b/doc/lchan-fsm.dot
@@ -38,4 +38,10 @@ labelloc=t; label="lchan FSM"
 	rtp -> WAIT_RLL_RTP_ESTABLISH [label="LCHAN_EV_RTP_READY",style=dotted]
 	rtp -> ESTABLISHED [label="LCHAN_EV_RTP_RELEASED",style=dotted]
 
+	ESTABLISHED -> WAIT_RR_CHAN_MODE_MODIFY_ACK [label="LCHAN_EV_REQUEST_MODE_MODIFY"]
+	WAIT_RR_CHAN_MODE_MODIFY_ACK -> WAIT_RSL_CHAN_MODE_MODIFY_ACK [label="LCHAN_EV_RR_CHAN_MODE_MODIFY_ACK"]
+	WAIT_RSL_CHAN_MODE_MODIFY_ACK -> WAIT_RLL_RTP_ESTABLISH [label="LCHAN_EV_RSL_CHAN_MODE_MODIFY_ACK\nwhen adding RTP"]
+	WAIT_RSL_CHAN_MODE_MODIFY_ACK -> ESTABLISHED [label="LCHAN_EV_RSL_CHAN_MODE_MODIFY_ACK\nno change to RTP"]
+	WAIT_RR_CHAN_MODE_MODIFY_ACK -> BORKEN [label="error/timeout",style=dashed]
+	WAIT_RSL_CHAN_MODE_MODIFY_ACK -> BORKEN [label="error/timeout",style=dashed]
 }
diff --git a/doc/lchan.msc b/doc/lchan.msc
index e2caa4875..b0e32d684 100644
--- a/doc/lchan.msc
+++ b/doc/lchan.msc
@@ -129,6 +129,26 @@ msc {
 	...;
 	...;
 
+	ms rbox mgwep [label="On Mode Modify (e.g. change a TCH lchan from signalling to voice)"];
+	lchan abox lchan [label="LCHAN_ST_\nWAIT_RR_CHAN_\nMODE_MODIFY_ACK"];
+	ms <= lchan [label="RR Chan Mode Modif"];
+	...;
+	ms => lchan [label="RR Chan Mode Modif Ack"];
+	lchan abox lchan [label="LCHAN_ST_\nWAIT_RSL_CHAN_\nMODE_MODIFY_ACK"];
+	ms <= lchan [label="RSL MT Mode Modify Req"];
+	...;
+	ms => lchan [label="RSL MT Mode Modify Ack"];
+	--- [label="IF adding RTP stream"];
+	lchan abox lchan [label="LCHAN_ST_WAIT_\nRLL_RTP_ESTABLISH\nT3101"];
+	lchan rbox rtp [label="See above at 'LCHAN_RTP_EV_LCHAN_READY'"];
+	--- [label="IF not adding RTP stream"];
+	lchan abox lchan [label="LCHAN_ST_\nESTABLISHED"];
+	--- [label="END: whether adding voice stream"];
+
+	...;
+	...;
+	...;
+
 	ms rbox mgwep [label="When the MS or BTS release the lchan"];
 	lchan abox lchan [label="LCHAN_ST_\nESTABLISHED"];
 	ms -> lchan [label="RLL Release Ind for SAPI=0"];