+1. Each independent transmitter in a wireless device (usually there is only one
+transmitter per device) should have a SINGLE rfkill class attached to it.
+
+2. If the device does not have any sort of hardware assistance to allow the
+driver to rfkill the device, the driver should emulate it by taking all actions
+required to silence the transmitter.
+
+3. If it is impossible to silence the transmitter (i.e. it still emits energy,
+even if it is just in brief pulses, when there is no data to transmit and there
+is no hardware support to turn it off) do NOT lie to the users. Do not attach
+it to a rfkill class. The rfkill subsystem does not deal with data
+transmission, it deals with energy emission. If the transmitter is emitting
+energy, it is not blocked in rfkill terms.
+
+4. It doesn't matter if the device has multiple rfkill input lines affecting
+the same transmitter, their combined state is to be exported as a single state
+per transmitter (see rule 1).
+
+This rule exists because users of the rfkill subsystem expect to get (and set,
+when possible) the overall transmitter rfkill state, not of a particular rfkill
+line.
+
+Example of a WLAN wireless driver connected to the rfkill subsystem:
+--------------------------------------------------------------------
+
+A certain WLAN card has one input pin that causes it to block the transmitter
+and makes the status of that input pin available (only for reading!) to the
+kernel driver. This is a hard rfkill input line (it cannot be overridden by
+the kernel driver).
+
+The card also has one PCI register that, if manipulated by the driver, causes
+it to block the transmitter. This is a soft rfkill input line.
+
+It has also a thermal protection circuitry that shuts down its transmitter if
+the card overheats, and makes the status of that protection available (only for
+reading!) to the kernel driver. This is also a hard rfkill input line.
+
+If either one of these rfkill lines are active, the transmitter is blocked by
+the hardware and forced offline.
+
+The driver should allocate and attach to its struct device *ONE* instance of
+the rfkill class (there is only one transmitter).
+
+It can implement the get_state() hook, and return RFKILL_STATE_HARD_BLOCKED if
+either one of its two hard rfkill input lines are active. If the two hard
+rfkill lines are inactive, it must return RFKILL_STATE_SOFT_BLOCKED if its soft
+rfkill input line is active. Only if none of the rfkill input lines are
+active, will it return RFKILL_STATE_UNBLOCKED.
+
+Since the device has a hardware rfkill line, it IS subject to state changes
+external to rfkill. Therefore, the driver must make sure that it calls
+rfkill_force_state() to keep the status always up-to-date, and it must do a
+rfkill_force_state() on resume from sleep.
+
+Every time the driver gets a notification from the card that one of its rfkill
+lines changed state (polling might be needed on badly designed cards that don't
+generate interrupts for such events), it recomputes the rfkill state as per
+above, and calls rfkill_force_state() to update it.
+
+The driver should implement the toggle_radio() hook, that:
+
+1. Returns an error if one of the hardware rfkill lines are active, and the
+caller asked for RFKILL_STATE_UNBLOCKED.
+
+2. Activates the soft rfkill line if the caller asked for state
+RFKILL_STATE_SOFT_BLOCKED. It should do this even if one of the hard rfkill
+lines are active, effectively double-blocking the transmitter.
+
+3. Deactivates the soft rfkill line if none of the hardware rfkill lines are
+active and the caller asked for RFKILL_STATE_UNBLOCKED.