Bluetooth: virtio_bt: fix device removal

Bluetooth: virtio_bt: fix device removal

Device removal is clearly out of virtio spec: it attempts to remove
unused buffers from a VQ before invoking device reset. To fix, make
open/close NOPs and do all cleanup/setup in probe/remove.

NB: This is a hacky way to handle this - virtbt_{open,close} as NOP is
not really what a driver is supposed to be doing. These are transport
enable/disable callbacks from the BT core towards the driver. It maps to
a device being enabled/disabled by something like bluetoothd for
example. So if disabled, users expect that no resources/queues are in
use.  It does work with all other transports like USB, SDIO, UART etc.
There should be no buffer used if the device is powered off. We also
don’t have any USB URBs in-flight if the transport is not active.

The way to implement a proper fix would be using vq reset if supported,
or even using a full device reset.

The cost of the hack is a single skb wasted on an unused bt device.

NB2: with this fix in place driver still suffers from a race condition
if an interrupt triggers while device is being reset.  To fix, in the
virtbt_close() callback we should deactivate all interrupts.  To be
fixed.

squashed fixup: bluetooth: virtio_bt: fix an error code in probe()

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20220811080943.198245-1-mst@redhat.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Tested-by: Igor Skalkin <Igor.Skalkin@opensynergy.com>