Fix mSBC MTU adjustment on Realtek USB adapters

.github/spellcheck-wordlist.txt

@@ -66,6 +66,7 @@ MPD
 oFono
 PipeWire
 PulseAudio
+Realtek
 UPower
 
 # Technical Words

doc/bluealsa.8.rst

@@ -100,6 +100,11 @@ OPTIONS
     It will reduce the gap between playbacks caused by Bluetooth audio
     transport acquisition.
 
+--disable-realtek-usb-fix
+    Since Linux kernel 5.14 Realtek USB adapters have required **bluealsa** to
+    apply a fix for mSBC. This option disables that fix and may be necessary
+    when using an earlier kernel.
+
 --a2dp-force-mono
     Force monophonic sound for A2DP profile.
 

src/ba-transport.c

@@ -887,7 +887,7 @@ 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, d->a->hci.type);
+	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, d->a);
 	t->bt_fd = fd;
 
 	return fd;

src/bluealsa-config.c

@@ -34,6 +34,8 @@ struct ba_config config = {
 
 	.volume_init_level = 0,
 
+	.disable_realtek_usb_fix = false,
+
 	/* CVSD is a mandatory codec */
 	.hfp.codecs.cvsd = true,
 #if ENABLE_MSBC

src/bluealsa-config.h

@@ -68,6 +68,9 @@ struct ba_config {
 	/* the initial volume level */
 	int volume_init_level;
 
+	/* disable alt-3 MTU for mSBC with Realtek USB adapters */
+	bool disable_realtek_usb_fix;
+
 	struct {
 
 		/* available HFP codecs */

src/hci.c

@@ -23,6 +23,9 @@
 #include <bluetooth/hci_lib.h>
 #include <bluetooth/sco.h>
 
+#include "ba-adapter.h"
+#include "bluealsa-config.h"
+#include "shared/bluetooth.h"
 #include "shared/log.h"
 
 /**
@@ -110,10 +113,10 @@ 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().
+ * @param a The adapter associated with sco_fd.
  * @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, int hci_type) {
+unsigned int hci_sco_get_mtu(int sco_fd, struct ba_adapter *a) {
 
 	struct sco_options options = { 0 };
 	struct bt_voice voice = { 0 };
@@ -135,10 +138,16 @@ unsigned int hci_sco_get_mtu(int sco_fd, int hci_type) {
 
 	/* XXX: It seems, that the MTU value returned by kernel btusb driver
 	 *      is incorrect. */
-	if ((hci_type & 0x0F) == HCI_USB) {
+	if ((a->hci.type & 0x0F) == HCI_USB) {
 		options.mtu = 48;
-		if (voice.setting == BT_VOICE_TRANSPARENT)
-			options.mtu = 24;
+		if (voice.setting == BT_VOICE_TRANSPARENT) {
+			if (a->chip.manufacturer == 0)
+				hci_get_version(a->hci.dev_id, &a->chip);
+			if (!config.disable_realtek_usb_fix && a->chip.manufacturer == BT_COMPID_REALTEK)
+				options.mtu = 72;
+			else
+				options.mtu = 24;
+		}
 		debug("USB adjusted SCO MTU: %d: %u", sco_fd, options.mtu);
 	}
 

src/hci.h

@@ -22,6 +22,8 @@
 #include <bluetooth/hci.h> /* IWYU pragma: keep */
 #include <bluetooth/hci_lib.h>
 
+#include "ba-adapter.h"
+
 int hci_get_version(int dev_id, struct hci_version *ver);
 
 /**
@@ -36,7 +38,8 @@ 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, int hci_type);
+
+unsigned int hci_sco_get_mtu(int sco_fd, struct ba_adapter *a);
 
 #define BT_BCM_PARAM_ROUTING_PCM       0x0
 #define BT_BCM_PARAM_ROUTING_TRANSPORT 0x1

src/main.c

@@ -156,6 +156,7 @@ int main(int argc, char **argv) {
 		{ "codec", required_argument, NULL, 'c' },
 		{ "initial-volume", required_argument, NULL, 17 },
 		{ "keep-alive", required_argument, NULL, 8 },
+		{ "disable-realtek-usb-fix", no_argument, NULL, 21 },
 		{ "a2dp-force-mono", no_argument, NULL, 6 },
 		{ "a2dp-force-audio-cd", no_argument, NULL, 7 },
 		{ "a2dp-volume", no_argument, NULL, 9 },
@@ -204,6 +205,7 @@ int main(int argc, char **argv) {
 					"  -c, --codec=NAME\t\tset enabled BT audio codecs\n"
 					"  --initial-volume=NUM\t\tinitial volume level [0-100]\n"
 					"  --keep-alive=SEC\t\tkeep Bluetooth transport alive\n"
+					"  --disable-realtek-usb-fix\tdisable fix for mSBC on Realtek USB\n"
 					"  --a2dp-force-mono\t\ttry to force monophonic sound\n"
 					"  --a2dp-force-audio-cd\t\ttry to force 44.1 kHz sampling\n"
 					"  --a2dp-volume\t\t\tnative volume control by default\n"
@@ -379,6 +381,10 @@ int main(int argc, char **argv) {
 			config.keep_alive_time = atof(optarg) * 1000;
 			break;
 
+		case 21 /* --disable-realtek-usb-fix */ :
+			config.disable_realtek_usb_fix = true;
+			break;
+
 		case 6 /* --a2dp-force-mono */ :
 			config.a2dp.force_mono = true;
 			break;

src/ofono.c

@@ -32,7 +32,6 @@
 #include <unistd.h>
 
 #include <bluetooth/bluetooth.h>
-#include <bluetooth/hci.h>
 #include <bluetooth/hci_lib.h>
 
 #include <gio/gio.h>
@@ -129,7 +128,7 @@ static int ofono_acquire_bt_sco(struct ba_transport *t) {
 #endif
 
 	t->bt_fd = fd;
-	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, t->d->a->hci.type);
+	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, t->d->a);
 	ba_transport_set_codec(t, codec);
 
 	debug("New oFono SCO link (codec: %#x): %d", codec, fd);
@@ -820,7 +819,7 @@ static void ofono_agent_new_connection(GDBusMethodInvocation *inv, void *userdat
 	debug("New oFono SCO link (codec: %#x): %d", codec, fd);
 
 	t->bt_fd = fd;
-	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, t->d->a->hci.type);
+	t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, t->d->a);
 	ba_transport_set_codec(t, codec);
 
 	pthread_mutex_unlock(&t->bt_fd_mtx);

src/sco.c

@@ -144,7 +144,7 @@ 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, a->hci.type);
+		t->mtu_read = t->mtu_write = hci_sco_get_mtu(fd, a);
 		fd = -1;
 
 		pthread_mutex_unlock(&t->bt_fd_mtx);

src/shared/bluetooth.h

@@ -21,6 +21,7 @@
 #define BT_COMPID_BROADCOM           0x000F
 #define BT_COMPID_APPLE              0x004C
 #define BT_COMPID_APT                0x004F
+#define BT_COMPID_REALTEK            0x005D
 #define BT_COMPID_SAMSUNG_ELEC       0x0075
 #define BT_COMPID_QUALCOMM_TECH      0x00D7
 #define BT_COMPID_SONY               0x012D

test/Makefile.am

@@ -156,6 +156,7 @@ test_utils_SOURCES = \
 	../src/shared/log.c \
 	../src/shared/nv.c \
 	../src/shared/rt.c \
+	../src/bluealsa-config.c \
 	../src/hci.c \
 	../src/utils.c \
 	test-utils.c