Bluetooth: Report invalid RSSI for service discovery and background scan

When using Start Service Discovery and when background scanning is used
to report devices, the RSSI is reported or the value 127 is provided in
case RSSI in unavailable.

For Start Discovery the value 0 is reported to keep backwards
compatibility with the existing users.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

include/net/bluetooth/hci_core.h

@@ -75,6 +75,7 @@ struct discovery_state {
 	u32			last_adv_flags;
 	u8			last_adv_data[HCI_MAX_AD_LENGTH];
 	u8			last_adv_data_len;
+	bool			report_invalid_rssi;
 	s8			rssi;
 	u16			uuid_count;
 	u8			(*uuids)[16];
@@ -506,11 +507,13 @@ static inline void discovery_init(struct hci_dev *hdev)
 	INIT_LIST_HEAD(&hdev->discovery.all);
 	INIT_LIST_HEAD(&hdev->discovery.unknown);
 	INIT_LIST_HEAD(&hdev->discovery.resolve);
+	hdev->discovery.report_invalid_rssi = true;
 	hdev->discovery.rssi = HCI_RSSI_INVALID;
 }
 
 static inline void hci_discovery_filter_clear(struct hci_dev *hdev)
 {
+	hdev->discovery.report_invalid_rssi = true;
 	hdev->discovery.rssi = HCI_RSSI_INVALID;
 	hdev->discovery.uuid_count = 0;
 	kfree(hdev->discovery.uuids);

net/bluetooth/mgmt.c

@@ -3912,6 +3912,7 @@ static int start_discovery(struct sock *sk, struct hci_dev *hdev,
 	hci_discovery_filter_clear(hdev);
 
 	hdev->discovery.type = cp->type;
+	hdev->discovery.report_invalid_rssi = false;
 
 	hci_req_init(&req, hdev);
 
@@ -7022,8 +7023,15 @@ void mgmt_device_found(struct hci_dev *hdev, bdaddr_t *bdaddr, u8 link_type,
 
 	memset(buf, 0, sizeof(buf));
 
-	/* Reset invalid RSSI to 0 to keep backwards API compliance */
-	if (rssi == HCI_RSSI_INVALID)
+	/* In case of device discovery with BR/EDR devices (pre 1.2), the
+	 * RSSI value was reported as 0 when not available. This behavior
+	 * is kept when using device discovery. This is required for full
+	 * backwards compatibility with the API.
+	 *
+	 * However when using service discovery, the value 127 will be
+	 * returned when the RSSI is not available.
+	 */
+	if (rssi == HCI_RSSI_INVALID && !hdev->discovery.report_invalid_rssi)
 		rssi = 0;
 
 	bacpy(&ev->addr.bdaddr, bdaddr);