codec_pref: check bts codec support

The vty option bts->codec-support allows the user to set the supported
codecs per BTS level. However, those values are currently only used to
make the handover decision but the logic that handles the BSSMAP
ASSIGNMENT REQUEST does not check those flags.

- Do not ignore bts->codec-support flags on BSSMAP ASSIGNMENT REQUEST

Change-Id: I285234e9c81de74d9fb9907fca2c443b08537435
Closes: OS#3361

2 files changed, 42 insertions, 4 deletions

diff --git a/src/osmo-bsc/codec_pref.c b/src/osmo-bsc/codec_pref.c
index ee0760a59..d2887ac60 100644
--- a/src/osmo-bsc/codec_pref.c
+++ b/src/osmo-bsc/codec_pref.c
@@ -23,6 +23,7 @@
 #include <osmocom/gsm/gsm0808_utils.h>
 #include <osmocom/bsc/bsc_msc_data.h>
 #include <osmocom/bsc/codec_pref.h>
+#include <osmocom/bsc/gsm_data.h>
 
 /* Helper function for match_codec_pref(), looks up a matching chan mode for
  * a given permitted speech value */
@@ -130,6 +131,34 @@ static bool test_codec_pref(const struct gsm0808_channel_type *ct,
 	return false;
 }
 
+/* Helper function to check if the given permitted speech value is supported
+ * by the BTS. (vty option bts->codec-support). */
+static bool test_codec_support_bts(struct gsm_bts *bts, uint8_t perm_spch)
+{
+	switch (perm_spch) {
+	case GSM0808_PERM_FR1:
+		/* GSM-FR is always supported by all BTSs. There is also no way to
+		 * selectively disable GSM-RF per BTS via VTY. */
+		return true;
+	case GSM0808_PERM_FR2:
+		if (bts->codec.efr)
+			return true;
+	case GSM0808_PERM_FR3:
+		if (bts->codec.amr)
+			return true;
+	case GSM0808_PERM_HR1:
+		if (bts->codec.hr)
+			return true;
+	case GSM0808_PERM_HR3:
+		if (bts->codec.amr)
+			return true;
+	default:
+		return false;
+	}
+
+	return false;
+}
+
 /*! Helper function for bssmap_handle_assignm_req(), matches the codec
  *  preferences from the MSC with the codec preferences
  *  \param[out] full_rate '1' if full-rate, '0' if half-rate, '-1' if no match
@@ -137,17 +166,26 @@ static bool test_codec_pref(const struct gsm0808_channel_type *ct,
  *  \param[in] ct GSM 08.08 channel type
  *  \param[in] scl GSM 08.08 speech codec list
  *  \param[in] msc MSC data [for configuration]
+ *  \param[in] bts BTS data [for configuration]
  *  \returns 0 on success, -1 in case no match was found */
-int match_codec_pref(int *full_rate, enum gsm48_chan_mode *chan_mode,
-		     const struct gsm0808_channel_type *ct,
-		     const struct gsm0808_speech_codec_list *scl, const struct bsc_msc_data *msc)
+int match_codec_pref(int *full_rate, enum gsm48_chan_mode *chan_mode, const struct gsm0808_channel_type *ct,
+		     const struct gsm0808_speech_codec_list *scl, const struct bsc_msc_data *msc, struct gsm_bts *bts)
 {
 	unsigned int i;
 	uint8_t perm_spch;
 	bool match = false;
 
 	for (i = 0; i < msc->audio_length; i++) {
+		/* Pick a permitted speech value from the global codec configuration list */
 		perm_spch = audio_support_to_gsm88(msc->audio_support[i]);
+
+		/* Check this permitted speech value against the BTS specific parameters.
+		 * if the BTS does not support the codec, try the next one */
+		if (test_codec_support_bts(bts, perm_spch) == false)
+			continue;
+
+		/* Match the permitted speech value against the codec lists that were
+		 * advertised by the MS and the MSC */
 		if (test_codec_pref(ct, scl, perm_spch)) {
 			match = true;
 			break;
diff --git a/src/osmo-bsc/osmo_bsc_bssap.c b/src/osmo-bsc/osmo_bsc_bssap.c
index 96cc2c59d..887a86682 100644
--- a/src/osmo-bsc/osmo_bsc_bssap.c
+++ b/src/osmo-bsc/osmo_bsc_bssap.c
@@ -680,7 +680,7 @@ static int bssmap_handle_assignm_req(struct gsm_subscriber_connection *conn,
 
 		/* Match codec information from the assignment command against the
 		 * local preferences of the BSC */
-		rc = match_codec_pref(&full_rate, &chan_mode, &ct, scl_ptr, msc);
+		rc = match_codec_pref(&full_rate, &chan_mode, &ct, scl_ptr, msc, conn_get_bts(conn));
 		if (rc < 0) {
 			LOGP(DMSC, LOGL_ERROR, "No supported audio type found for channel_type ="
 			     " { ch_indctr=0x%x, ch_rate_type=0x%x, perm_spch=[ %s] }\n",