fixup for Early IMM ASS: use proper TSC

Testing has shown that the Training Sequence Code in pre-chan-ack mode
is inaccurate (only worked with a BSIC that incidentally yielded the
same TSC value as the wrong TSC value sent in the IMM ASS msg).

Move the code setting the correct TSC and TSC-Set to the first stage of
channel activation (lchan_fsm_wait_ts_ready_onenter()) so that it is
available for both pre-chan-ack and pre-ts-ack Early-IA modes.

Have a separate function for setting the preliminary values requested in
Channel Activation (lchan->activate.*) into the accepted operative
places (lchan->*). Call this early for early-IA modes.

Hence the TSC and TSC-Set used in the early IMM ASS message is now the
correct one, and the same as sent during Channel Activation.
There shouldn't be any, but if there are other values besides TSC
suffering from the same problem, they are now also set to the right
values before sending IMM ASS early.

Related: SYS#5559
Related: I4479244b0c53648e62e84e1ebf986f51d659484f (osmo-ttcn3-hacks)
Change-Id: I9f26074154600d854a0b3baee2f38a6666f4cb56

1 files changed, 40 insertions, 16 deletions

diff --git a/src/osmo-bsc/lchan_fsm.c b/src/osmo-bsc/lchan_fsm.c
index c390662a1..1b59b453d 100644
--- a/src/osmo-bsc/lchan_fsm.c
+++ b/src/osmo-bsc/lchan_fsm.c
@@ -672,6 +672,8 @@ static int lchan_send_imm_ass(struct osmo_fsm_inst *fi)
 	return rc;
 }
 
+static void post_activ_ack_accept_preliminary_settings(struct gsm_lchan *lchan);
+
 static void lchan_fsm_wait_ts_ready_onenter(struct osmo_fsm_inst *fi, uint32_t prev_state)
 {
 	struct gsm_lchan *lchan = lchan_fi_lchan(fi);
@@ -717,6 +719,17 @@ static void lchan_fsm_wait_ts_ready_onenter(struct osmo_fsm_inst *fi, uint32_t p
 	if (lchan_activate_set_ch_mode_rate_and_mr_config(lchan))
 		return;
 
+	/* If enabling VAMOS mode and no specific TSC Set was selected, make sure to select a sane TSC Set by
+	 * default: Set 1 for the primary and Set 2 for the shadow lchan. For non-VAMOS lchans, TSC Set 1. */
+	if (lchan->activate.info.tsc_set > 0)
+		lchan->activate.tsc_set = lchan->activate.info.tsc_set;
+	else
+		lchan->activate.tsc_set = lchan->vamos.is_secondary ? 2 : 1;
+
+	/* Use the TSC provided in the modification request, if any. Otherwise use the timeslot's configured
+	 * TSC. */
+	lchan->activate.tsc = (lchan->activate.info.tsc >= 0) ? lchan->activate.info.tsc : gsm_ts_tsc(lchan->ts);
+
 	use_mgwep_ci = lchan_use_mgw_endpoint_ci_bts(lchan);
 
 	LOG_LCHAN(lchan, LOGL_INFO,
@@ -742,7 +755,13 @@ static void lchan_fsm_wait_ts_ready_onenter(struct osmo_fsm_inst *fi, uint32_t p
 
 	if (lchan->activate.info.imm_ass_time == IMM_ASS_TIME_PRE_TS_ACK) {
 		/* Send the Immediate Assignment even before the timeslot is ready, saving a dyn TS timeslot roundtrip
-		 * on Abis (experimental). */
+		 * on Abis (experimental).
+		 *
+		 * Until the Channel Activation ACK is received, various values still are preliminary and hence live in
+		 * lchan->activate.*. We're doing things early here and need e.g. an accurate lchan->tsc, so already
+		 * copy the preliminary values from lchan->activate.* into the operative places in lchan->* prematurely.
+		 */
+		post_activ_ack_accept_preliminary_settings(lchan);
 		lchan_send_imm_ass(fi);
 	}
 }
@@ -801,19 +820,13 @@ static void lchan_fsm_wait_activ_ack_onenter(struct osmo_fsm_inst *fi, uint32_t
 		break;
 	}
 
+	/* rsl_tx_chan_activ() and build_encr_info() access lchan->encr, make sure it reflects the values requested for
+	 * activation.
+	 * TODO: rather leave it in lchan->activate.info.encr until the ACK is received, which means that
+	 * rsl_tx_chan_activ() should use lchan->activate.info.encr and build_encr_info() should be passed encr as an
+	 * explicit argument. */
 	lchan->encr = lchan->activate.info.encr;
 
-	/* If enabling VAMOS mode and no specific TSC Set was selected, make sure to select a sane TSC Set by
-	 * default: Set 1 for the primary and Set 2 for the shadow lchan. For non-VAMOS lchans, TSC Set 1. */
-	if (lchan->activate.info.tsc_set > 0)
-		lchan->activate.tsc_set = lchan->activate.info.tsc_set;
-	else
-		lchan->activate.tsc_set = lchan->vamos.is_secondary ? 2 : 1;
-
-	/* Use the TSC provided in the modification request, if any. Otherwise use the timeslot's configured
-	 * TSC. */
-	lchan->activate.tsc = (lchan->activate.info.tsc >= 0) ? lchan->activate.info.tsc : gsm_ts_tsc(lchan->ts);
-
 	rc = rsl_tx_chan_activ(lchan, act_type, ho_ref);
 	if (rc) {
 		lchan_fail_to(LCHAN_ST_UNUSED, "Tx Chan Activ failed: %s (%d)", strerror(-rc), rc);
@@ -825,7 +838,13 @@ static void lchan_fsm_wait_activ_ack_onenter(struct osmo_fsm_inst *fi, uint32_t
 
 	if (lchan->activate.info.imm_ass_time == IMM_ASS_TIME_PRE_CHAN_ACK) {
 		/* Send the Immediate Assignment directly after the Channel Activation request, saving one Abis
-		 * roundtrip between ChanRqd and Imm Ass. */
+		 * roundtrip between ChanRqd and Imm Ass.
+		 *
+		 * Until the Channel Activation ACK is received, various values still are preliminary and hence live in
+		 * lchan->activate.*. We're doing things early here and need e.g. an accurate lchan->tsc, so already
+		 * copy the preliminary values from lchan->activate.* into the operative places in lchan->* prematurely.
+		 */
+		post_activ_ack_accept_preliminary_settings(lchan);
 		lchan_send_imm_ass(fi);
 	}
 }
@@ -886,15 +905,20 @@ static void lchan_fsm_wait_activ_ack(struct osmo_fsm_inst *fi, uint32_t event, v
 	}
 }
 
-static void lchan_fsm_post_activ_ack(struct osmo_fsm_inst *fi)
+static void post_activ_ack_accept_preliminary_settings(struct gsm_lchan *lchan)
 {
-	struct gsm_lchan *lchan = lchan_fi_lchan(fi);
-
 	lchan->current_ch_mode_rate = lchan->activate.ch_mode_rate;
 	lchan->current_mr_conf = lchan->activate.mr_conf_filtered;
 	lchan->vamos.enabled = lchan->activate.info.vamos;
 	lchan->tsc_set = lchan->activate.tsc_set;
 	lchan->tsc = lchan->activate.tsc;
+}
+
+static void lchan_fsm_post_activ_ack(struct osmo_fsm_inst *fi)
+{
+	struct gsm_lchan *lchan = lchan_fi_lchan(fi);
+
+	post_activ_ack_accept_preliminary_settings(lchan);
 	LOG_LCHAN(lchan, LOGL_INFO, "Rx Activ ACK %s\n",
 		  gsm48_chan_mode_name(lchan->current_ch_mode_rate.chan_mode));