[PATCH] adapter: add DisableDiscoveryOnConnect option for combo chip coexistence

[StefanCondorache <condorachest@gmail.com>]

On systems with combo chips (shared Wi-Fi/Bluetooth antenna), background
LE scanning for auto-connect devices competes with active connections,
causing audio stuttering and Wi-Fi packet loss due to antenna
multiplexing via Packet Traffic Arbitration (PTA).

Add a DisableDiscoveryOnConnect boolean option to the [General] section
of main.conf. When enabled and an active connection exists, the option
suppresses adding devices to the kernel auto-connect list in
adapter_auto_connect_add() on kernels supporting KERNEL_CONN_CONTROL,
and gates trigger_passive_scanning() on older kernels.

The option defaults to false to preserve existing behavior.

Signed-off-by: StefanCondorache <condorachest@gmail.com>
---
 src/adapter.c | 24 ++++++++++++++++++++++++
 src/btd.h     |  2 ++
 src/main.c    |  4 ++++
 src/main.conf |  6 ++++++
 4 files changed, 36 insertions(+)

diff --git a/src/adapter.c b/src/adapter.c
index 6df66b3e0..4a18adfe0 100644
--- a/src/adapter.c
+++ b/src/adapter.c
@@ -1594,6 +1594,18 @@ static void trigger_passive_scanning(struct btd_adapter *adapter)
 	if (!adapter->connect_list)
 		return;
 
+	/*
+	 * If the user has enabled DisableDiscoveryOnConnect, suppress
+	 * passive scanning whenever there is at least one active connection.
+	 * This prevents antenna multiplexing conflicts on combo chips where
+	 * Wi-Fi and Bluetooth share the same 2.4 GHz radio, which causes
+	 * audio drops and Wi-Fi packet loss during background scans.
+	 */
+	if (btd_opts.disable_discovery_on_connect && adapter->connections) {
+		DBG("suppress passive scan: active connection present");
+		return;
+	}
+
 	adapter->passive_scan_timeout = timeout_add_seconds(CONN_SCAN_TIMEOUT,
 					passive_scanning_timeout, adapter,
 					NULL);
@@ -5717,6 +5729,18 @@ void adapter_auto_connect_add(struct btd_adapter *adapter,
 		return;
 	}
 
+	/*
+	 * If DisableDiscoveryOnConnect is enabled, suppress adding devices
+	 * to the kernel auto-connect list while an active connection exists.
+	 * On combo chips (shared Wi-Fi/Bluetooth antenna), the kernel's
+	 * background scanning for auto-connect devices competes with active
+	 * connections, causing audio drops and Wi-Fi packet loss.
+	 */
+	if (btd_opts.disable_discovery_on_connect && adapter->connections) {
+		DBG("suppress kernel auto-connect: active connection present");
+		return;
+	}
+
 	bdaddr = device_get_address(device);
 	bdaddr_type = btd_device_get_bdaddr_type(device);
 
diff --git a/src/btd.h b/src/btd.h
index c84a600d1..07c4d85ba 100644
--- a/src/btd.h
+++ b/src/btd.h
@@ -144,6 +144,8 @@ struct btd_opts {
 	bool		experimental;
 	bool		testing;
 	bool		filter_discoverable;
+	bool		disable_discovery_on_connect;
+
 	struct queue	*kernel;
 
 	uint16_t	did_source;
diff --git a/src/main.c b/src/main.c
index 818f7c06e..d7ddf5643 100644
--- a/src/main.c
+++ b/src/main.c
@@ -92,6 +92,7 @@ static const char *supported_options[] = {
 	"KernelExperimental",
 	"RemoteNameRequestRetryDelay",
 	"FilterDiscoverable",
+	"DisableDiscoveryOnConnect",
 	NULL
 };
 
@@ -1072,6 +1073,8 @@ static void parse_general(GKeyFile *config)
 					0, UINT32_MAX);
 	parse_config_bool(config, "General", "FilterDiscoverable",
 						&btd_opts.filter_discoverable);
+	parse_config_bool(config, "General", "DisableDiscoveryOnConnect",
+					&btd_opts.disable_discovery_on_connect);
 }
 
 static void parse_gatt_cache(GKeyFile *config)
@@ -1283,6 +1286,7 @@ static void init_defaults(void)
 	btd_opts.name_request_retry_delay = DEFAULT_NAME_REQUEST_RETRY_DELAY;
 	btd_opts.secure_conn = SC_ON;
 	btd_opts.filter_discoverable = true;
+	btd_opts.disable_discovery_on_connect = false;
 
 	btd_opts.defaults.num_entries = 0;
 	btd_opts.defaults.br.page_scan_type = 0xFFFF;
diff --git a/src/main.conf b/src/main.conf
index d31dd1b8f..22507c465 100644
--- a/src/main.conf
+++ b/src/main.conf
@@ -157,6 +157,12 @@
 # some stacks) or when testing bad/unintended behavior.
 #FilterDiscoverable = true
 
+# Disables background LE passive scanning when an active connection is
+# established. Recommended for combo chips (shared Wi-Fi/Bluetooth antenna)
+# to prevent audio stuttering and packet loss caused by antenna multiplexing.
+# Defaults to false.
+#DisableDiscoveryOnConnect = false
+
 [BR]
 # The following values are used to load default adapter parameters for BR/EDR.
 # BlueZ loads the values into the kernel before the adapter is powered if the
-- 
2.53.0