Bluetooth: hci_qca: add PM support

Bluetooth: hci_qca: add PM support

Add PM suspend/resume callbacks for hci_qca driver.

BT host will make sure both Rx and Tx go into sleep state in
qca_suspend. Without this, Tx may still remain in awake state, which
prevents BTSOC from entering deep sleep. For example, BlueZ will send
Set Event Mask to device when suspending and this will wake the device
Rx up. However, the Tx idle timeout on the host side is 2000 ms. If the
host is suspended before its Tx idle times out, it won't send
HCI_IBS_SLEEP_IND to the device and the device Rx will remain awake.

We implement this by canceling relevant work in workqueue, sending
HCI_IBS_SLEEP_IND to the device and then waiting HCI_IBS_SLEEP_IND sent
by the device.

In order to prevent the device from being awaken again after qca_suspend
is called, we introduce QCA_SUSPEND flag. QCA_SUSPEND is set in the
beginning of qca_suspend to indicate system is suspending and that we'd
like to ignore any further wake events.

With QCA_SUSPEND and spinlock, we can avoid race condition, e.g. if
qca_enqueue acquires qca->hci_ibs_lock before qca_suspend calls
cancel_work_sync and then qca_enqueue adds a new qca->ws_awake_device
work after the previous one is cancelled.

If BTSOC wants to wake the whole system up after qca_suspend is called,
it will keep sending HCI_IBS_WAKE_IND and uart driver will take care of
waking the system. For example, uart driver will reconfigure its Rx pin
to a normal GPIO pin and enable irq wake on that pin when suspending.
Once host detects Rx falling, the system will begin resuming. Then, the
BT host clears QCA_SUSPEND flag in qca_resume and begins dealing with
normal HCI packets. By doing so, only a few HCI_IBS_WAKE_IND packets are
lost and there is no data packet loss.

Signed-off-by: Claire Chang <tientzu@chromium.org>
Reviewed-by: Balakrishna Godavarthi <bgodavar@codeaurora.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>