Change in osmo-bsc[master]: lchan_fsm: Avoid inheriting bs_power from old lchan

[pespin]

pespin has submitted this change. ( https://gerrit.osmocom.org/c/osmo-bsc/+/25412 )

Change subject: lchan_fsm: Avoid inheriting bs_power from old lchan
......................................................................

lchan_fsm: Avoid inheriting bs_power from old lchan

So far we were inherting the bs_power in used when activating an lchan
for an MS for which we already had previous lchan. For instance, when an
MS is first assigned an SDCCH, and later on, it is assigned a TCH to
place a voice call.
Doing so is, however, not correct because current and old lchans may be
placed on different TS or even on different TRX, which means they will
have different BS Power restrictions. In the scenario described above,
for instance, an SDCCH could have been assigned on C0 and hence have
a bs_power of 0, and later on, whenever the TCH lchan as created, it
would have inherited the C0 bs_power despite it may have been possible
to use a different (lower) max bs power.
Furthermore, the lchan->bs_power_db basically stores the *maximum* bs
power reduction. Hence it makes not sense at all to copy over the value,
since it is anyway not updated from MS measurement reports so far
anyway.

Fixes: 997a257f8dabe5dd940a1271e56e676a871896d7
Related: SYS#4919
Change-Id: I4a7736aa9a1395e0cc118b98b69896bd0f1e94e6
---
M src/osmo-bsc/lchan_fsm.c
1 file changed, 9 insertions(+), 15 deletions(-)

Approvals:
  Jenkins Builder: Verified
  laforge: Looks good to me, but someone else must approve
  osmith: Looks good to me, but someone else must approve
  pespin: Looks good to me, approved



diff --git a/src/osmo-bsc/lchan_fsm.c b/src/osmo-bsc/lchan_fsm.c
index a18cba5..d06dbac 100644
--- a/src/osmo-bsc/lchan_fsm.c
+++ b/src/osmo-bsc/lchan_fsm.c
@@ -681,7 +681,7 @@
 	struct osmo_mgcpc_ep_ci *use_mgwep_ci;
 	struct gsm_lchan *old_lchan = lchan->activate.info.re_use_mgw_endpoint_from_lchan;
 	struct lchan_activate_info *info = &lchan->activate.info;
-	int ms_power_dbm;
+	int ms_power_dbm = bts->ms_max_power;
 
 	if (lchan->release.requested) {
 		lchan_fail("Release requested while activating");
@@ -691,23 +691,17 @@
 	lchan->conn = info->for_conn;
 
 	/* If there is a previous lchan, and the new lchan is on the same cell as previous one,
-	 * take over power values. Otherwise, use max power. */
+	 * take over MS power values. Otherwise, use configured MS max power. */
 	if (old_lchan && old_lchan->ts->trx->bts == bts) {
-		ms_power_dbm = ms_pwr_dbm(bts->band, old_lchan->ms_power);
-		lchan_update_ms_power_ctrl_level(lchan, ms_power_dbm >= 0 ? ms_power_dbm : bts->ms_max_power);
-		lchan->bs_power_db = old_lchan->bs_power_db;
-	} else {
-		lchan_update_ms_power_ctrl_level(lchan, bts->ms_max_power);
-		/* Upon last entering the UNUSED state, from lchan_reset():
-		 * - bs_power_db is still zero, 0dB reduction, output power = Pn. */
-
-		/* Default BS Power reduction value (in dB) */
-		if (bts->bs_power_ctrl.mode == GSM_PWR_CTRL_MODE_DYN_BTS)
-			lchan->bs_power_db = bts->bs_power_ctrl.bs_power_max_db;
-		else
-			lchan->bs_power_db = bts->bs_power_ctrl.bs_power_val_db;
+		if ((ms_power_dbm = ms_pwr_dbm(bts->band, old_lchan->ms_power)) == 0)
+			ms_power_dbm = bts->ms_max_power;
 	}
+	lchan_update_ms_power_ctrl_level(lchan, ms_power_dbm);
 
+	/* Default BS Power reduction value (in dB) */
+	lchan->bs_power_db = (bts->bs_power_ctrl.mode == GSM_PWR_CTRL_MODE_DYN_BTS) ?
+				bts->bs_power_ctrl.bs_power_max_db :
+				bts->bs_power_ctrl.bs_power_val_db;
 	/* BS Power Control is generally not allowed on the BCCH/CCCH carrier.
 	 * However, we allow it in the BCCH carrier power reduction mode of operation. */
 	if (lchan->ts->trx == bts->c0) {

-- 
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Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-Change-Id: I4a7736aa9a1395e0cc118b98b69896bd0f1e94e6
Gerrit-Change-Number: 25412
Gerrit-PatchSet: 1
Gerrit-Owner: pespin <pespin at sysmocom.de>
Gerrit-Reviewer: Hoernchen <ewild at sysmocom.de>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: dexter <pmaier at sysmocom.de>
Gerrit-Reviewer: fixeria <vyanitskiy at sysmocom.de>
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-Reviewer: neels <nhofmeyr at sysmocom.de>
Gerrit-Reviewer: osmith <osmith at sysmocom.de>
Gerrit-Reviewer: pespin <pespin at sysmocom.de>
Gerrit-MessageType: merged
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