From a66852525ab9287c3869b3983f04506f0484f422 Mon Sep 17 00:00:00 2001
From: Neels Hofmeyr <nhofmeyr@sysmocom.de>
Date: Mon, 6 Jun 2016 12:53:25 +0200
Subject: dyn PDCH: allow allocating TCH/F on TCH/F_PDCH slots

Remove check for dyn PDCH in _lc_find_trx(), instead call _lc_find_trx() via
_lc_find_bts() several times, so that pure TCH/F is preferred to TCH/F_PDCH.
Add this logic next to the other channel match decisions in chan_alloc().

BTW, the removed check in _lc_find_trx() whether PDCH is active is not
necessary, as described in the added comment for lchan_alloc().

Original patch idea by jolly, but split in two and implemented differently by
nhofmeyr.

Change-Id: I0c728b922656be03588b775638b610a93f8187d5
---
 openbsc/src/libbsc/chan_alloc.c | 38 +++++++++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/openbsc/src/libbsc/chan_alloc.c b/openbsc/src/libbsc/chan_alloc.c
index 37cdb278f..471578025 100644
--- a/openbsc/src/libbsc/chan_alloc.c
+++ b/openbsc/src/libbsc/chan_alloc.c
@@ -96,14 +96,7 @@ _lc_find_trx(struct gsm_bts_trx *trx, enum gsm_phys_chan_config pchan)
 		ts = &trx->ts[j];
 		if (!ts_is_usable(ts))
 			continue;
-		/* ip.access dynamic TCH/F + PDCH combination */
-		if (ts->pchan == GSM_PCHAN_TCH_F_PDCH &&
-		    pchan == GSM_PCHAN_TCH_F) {
-			/* we can only consider such a dynamic channel
-			 * if the PDCH is currently inactive */
-			if (ts->flags & TS_F_PDCH_MODE)
-				continue;
-		} else if (ts->pchan != pchan)
+		if (ts->pchan != pchan)
 			continue;
 		/* check if all sub-slots are allocated yet */
 		for (ss = 0; ss < subslots_per_pchan[pchan]; ss++) {
@@ -140,7 +133,12 @@ _lc_find_bts(struct gsm_bts *bts, enum gsm_phys_chan_config pchan)
 	return NULL;
 }
 
-/* Allocate a logical channel */
+/* Allocate a logical channel.
+ *
+ * For TCH/F, we may return a dynamic TCH/F_PDCH channel (but prefer a pure
+ * TCH/F). If we pick a TCH/F_PDCH time slot, PDCH will be disabled later on;
+ * there is no need to check whether PDCH mode is currently active, here.
+ */
 struct gsm_lchan *lchan_alloc(struct gsm_bts *bts, enum gsm_chan_t type,
 			      int allow_bigger)
 {
@@ -182,6 +180,14 @@ struct gsm_lchan *lchan_alloc(struct gsm_bts *bts, enum gsm_chan_t type,
 				if (lchan)
 					type = GSM_LCHAN_TCH_F;
 			}
+
+			/* try dynamic TCH/F_PDCH */
+			if (lchan == NULL) {
+				lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F_PDCH);
+				/* TCH/F_PDCH will be used as TCH/F */
+				if (lchan)
+					type = GSM_LCHAN_TCH_F;
+			}
 		}
 		break;
 	case GSM_LCHAN_TCH_F:
@@ -192,6 +198,14 @@ struct gsm_lchan *lchan_alloc(struct gsm_bts *bts, enum gsm_chan_t type,
 			if (lchan)
 				type = GSM_LCHAN_TCH_H;
 		}
+		/* If we don't have TCH/H either, try dynamic TCH/F_PDCH */
+		if (!lchan) {
+			lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F_PDCH);
+			/* TCH/F_PDCH used as TCH/F -- here, type is already
+			 * set to GSM_LCHAN_TCH_F, but for clarity's sake... */
+			if (lchan)
+				type = GSM_LCHAN_TCH_F;
+		}
 		break;
 	case GSM_LCHAN_TCH_H:
 		lchan =_lc_find_bts(bts, GSM_PCHAN_TCH_H);
@@ -201,6 +215,12 @@ struct gsm_lchan *lchan_alloc(struct gsm_bts *bts, enum gsm_chan_t type,
 			if (lchan)
 				type = GSM_LCHAN_TCH_F;
 		}
+		/* If we don't have TCH/F either, try dynamic TCH/F_PDCH */
+		if (!lchan) {
+			lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F_PDCH);
+			if (lchan)
+				type = GSM_LCHAN_TCH_F;
+		}
 		break;
 	default:
 		LOGP(DRLL, LOGL_ERROR, "Unknown gsm_chan_t %u\n", type);
-- 
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