* @param[in] cg The channel group on the device instance for which to list
* the values, or NULL. If this device instance doesn't
* have channel groups, this must not be != NULL.
+ * If cg is NULL, this function will return the "common" device
+ * instance options that are channel-group independent. Otherwise
+ * it will return the channel-group specific options.
* @param[in] key The configuration key (SR_CONF_*).
* @param[in,out] data A pointer to a GVariant where the list will be stored.
* The caller is given ownership of the GVariant and must thus