Bluetooth: Background scanning

This patch adds helpers to trigger and untrigger the background
scanning. As long as the number of triggers are greater than zero,
we keep the background scanning running. Once the number of triggers
reaches zero, it is stopped.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Refactor hci_disconn_complete_evt

hci_disconn_complete_evt() logic is more complicated than what it
should be, making it hard to follow and add new features. This patch
does some code refactoring by letting the main flow of the function
in first level of function scope.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Add support for BT_AUTO_CONN_ALWAYS

This patch adds support for the BT_AUTO_CONN_ALWAYS option which
configures the kernel to autonomously establish a connection to
certain device. This option configures the kernel to always
establish the connection, no matter the reason the connection was
terminated.

This feature is required by some LE profiles such as HID over GATT,
Health Termomether and Blood Pressure. These profiles require the
host autonomously connect to the device as soon as it enters in
connectable mode (start advertising) so the device is able to
delivery a notification or indication.

The auto connection procedure the BT_AUTO_CONN_ALWAYS option implements
is summarized as follows: when a new device configured with BT_AUTO_
CONN_ALWAYS is added to the connection parameter list, the background
scan is triggered. Once the target device is found in range, the kernel
creates a connection to the device. If the connection is established
successfully, the background scan is untriggered. If the target device
disconnects, the background scan is triggered again and the whole auto
connect procedure starts again.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Add support for BT_AUTO_CONN_LINK_LOSS option

This patch adds support for the BT_AUTO_CONN_LINK_LOSS option which
configures the kernel to autonomously reconnect to a certainn device
in case the connection is terminated by link loss (which maps to HCI
Connection Timeout error.

This feature is required by the majority of LE profiles such as
Proximity, Find Me, Cycling Speed and Cadence and Time.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Create start_background_scan helper

This patch creates the start_background_scan() function so it can
be reused in the next patch.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Temporarily stop background scanning on connection

Some LE controllers don't support scanning and initiating a connection
at the same time. So, for those controllers, we should temporarily
stop the background scanning and start it again once the connection
attempt is finished (successfully or not).

So this patch introduces the hci_check_background_scan() which checks
if the background scanning should be started.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Temporarily stop background scanning on discovery

If the user send a mgmt start discovery command while the background
scanning is running, we should temporarily stop it. Once the discovery
finishes, we start the background scanning again.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Fix background trigger/untrigger functions

This patch fixes to hci_trigger_background_scan() and hci_untrigger_
background_scan() so they can be called concurrently with the device
discovery procedure.

In hci_trigger_background_scan(), if it is the first trigger, we are
supposed to start the background scanning. However, if device discovery
is running, we should not send any HCI command. The background scanning
will be started once the discovery procedure is finished.

In hci_untrigger_background_scan(), if it is the last trigger, we are
supposed to stop the background scanning. However, if discovery is
running, it means the background is stopped so we don't need to send
any HCI command.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Fix hci_create_le_conn()

When a LE device we want automatically connect to is found during the
device discovery procedure, we create the connection. Since some LE
controllers don't support scanning and initiating state combination,
the scanning will be disabled therefore we should set the discovery
state to DISCOVERY_STOPPED

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Auto connection and power off/on

If hdev is closed (e.g. Mgmt power off command, RFKILL or controller is
reset), the established connections are dropped and no Disconnection
Complete Event is sent to host. This way, the background scan is not
triggered when devices configured with BT_AUTO_CONN_ALWAYS option
disconnect. To fix this issue, before dropping the LE connections, we
trigger the background scan for each connected device that requires
BT_AUTO_CONN_ALWAYS auto connection.

Moreover, once the adapter is powered on, we should start the background
scan if we have triggers registered. This way, we keep the background
scan running after a power off and power on sequence.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>