• Tzu-Jung Lee's avatar
    linux: remove state machine handling out of hci. · c15a5369
    Tzu-Jung Lee authored
    A controller may have more than one instance of state machine to
    handle multiple concurrent connections. It's hard to maintain
    another state machine in the hci package, and try to keep it
    sync'ed with the controller's state.
    
    When a controller accepts a connection, it moves from advertising
    state back to idle/ready state. The host has to explicitly enable
    it to advertise again.
    
    In the 4.0 spec, where there is only ne connection at a time,
    this is plain simple; always re-enable advertising when the
    conecction disconnects.
    
    Things get much more complicated when it comes to supporting
    multiple connections. First of all, there's no way for the host to
    query how many connections the controller support.  What the host
    can do is to re-enable the advertising right after it accepts a
    connection. However, when the number of connecetions reaches to the
    limit of the controller, different controller may have different
    implementation/behaviour.
    
    One controller may return "command success" while it doesn't really
    re-enable advertising on the spot, but waits until the number of
    connections drops. Other controllers may return "command disallowed"
    and expect you to retry later, and the host would need to re-eanable
    advertising when a connection disconects.
    
    Given that we can't
    
      * learn how many connections a controller supports,
      * query if the controller is really advertising or not
      * different controllers may have different implementations
    
    the best we can do in the low-level package is probably to make it
    transparent to the users, passing errors with more context.
    
    Users should learn the capability of the controller from the vendor,
    datasheet, or product description. And figure out which case is the
    controller when it reaches to its maximum concurrent connection, and
    handle it accordingly - retry at the disconnect event or not.
    c15a5369
hci.go 12.2 KB