Apply SCO MTU workaround only for USB adapters

Closes #512

src/ba-transport.c

@@ -709,7 +709,7 @@ static int transport_acquire_bt_sco(struct ba_transport *t) {
 
 	debug("New SCO link: %s: %d", batostr_(&d->addr), fd);
 
-	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd);
+	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, d->a->hci.type);
 	t->bt_fd = fd;
 
 	return fd;

src/hci.c

@@ -109,9 +109,10 @@ int hci_sco_connect(int sco_fd, const bdaddr_t *ba, uint16_t voice) {
  * Get read/write MTU for given SCO socket.
  *
  * @param sco_fd File descriptor of opened SCO socket.
+ * @param hci_type The type of the HCI returned by hci_devinfo().
  * @return On success this function returns MTU value. Otherwise, 0 is returned and
  *   errno is set to indicate the error. */
-unsigned int hci_sco_get_mtu(int sco_fd) {
+unsigned int hci_sco_get_mtu(int sco_fd, int hci_type) {
 
 	struct sco_options options = { 0 };
 	struct bt_voice voice = { 0 };
@@ -131,12 +132,14 @@ unsigned int hci_sco_get_mtu(int sco_fd) {
 
 	debug("SCO link socket MTU: %d: %u", sco_fd, options.mtu);
 
-	/* XXX: It seems, that the MTU value returned by kernel
-	 *      is incorrect (or our interpretation of it). */
-
-	options.mtu = 48;
-	if (voice.setting == BT_VOICE_TRANSPARENT)
-		options.mtu = 24;
+	/* XXX: It seems, that the MTU value returned by kernel btusb driver
+	 *      is incorrect. */
+	if ((hci_type & 0x0F) == HCI_USB) {
+		options.mtu = 48;
+		if (voice.setting == BT_VOICE_TRANSPARENT)
+			options.mtu = 24;
+		debug("USB adjusted SCO MTU: %d: %u", sco_fd, options.mtu);
+	}
 
 	return options.mtu;
 }

src/hci.h

@@ -48,7 +48,7 @@ int hci_get_version(int dev_id, struct hci_version *ver);
 
 int hci_sco_open(int dev_id);
 int hci_sco_connect(int sco_fd, const bdaddr_t *ba, uint16_t voice);
-unsigned int hci_sco_get_mtu(int sco_fd);
+unsigned int hci_sco_get_mtu(int sco_fd, int hci_type);
 
 #define BT_BCM_PARAM_ROUTING_PCM       0x0
 #define BT_BCM_PARAM_ROUTING_TRANSPORT 0x1

src/ofono.c

@@ -407,7 +407,7 @@ static void ofono_agent_new_connection(GDBusMethodInvocation *inv, void *userdat
 	debug("New oFono SCO connection (codec: %#x): %d", codec, fd);
 
 	t->bt_fd = fd;
-	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd);
+	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, t->d->a->hci.type);
 	ba_transport_set_codec(t, codec);
 
 	pthread_mutex_unlock(&t->bt_fd_mtx);

src/sco.c

@@ -129,7 +129,7 @@ static void *sco_dispatcher_thread(struct ba_adapter *a) {
 		pthread_mutex_lock(&t->bt_fd_mtx);
 
 		t->bt_fd = fd;
-		t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd);
+		t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, a->hci.type);
 		fd = -1;
 
 		pthread_mutex_unlock(&t->bt_fd_mtx);