iwlwifi: mvm: don't allow sched scans without matches to be started

BugLink: http://bugs.launchpad.net/bugs/1553179

commit 5e56276e upstream.

The firmware can perform a scheduled scan with not matchsets passed,
but it can't send notification that results were found.  Since the
userspace then cannot know when we got new results and the firmware
wouldn't trigger a wake in case we are sleeping, it's better not to
allow scans without matchsets.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=110831Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/wireless/iwlwifi/mvm/scan.c

@@ -1267,6 +1267,10 @@ int iwl_mvm_sched_scan_start(struct iwl_mvm *mvm,
 		return -EBUSY;
 	}
 
+	/* we don't support "match all" in the firmware */
+	if (!req->n_match_sets)
+		return -EOPNOTSUPP;
+
 	ret = iwl_mvm_check_running_scans(mvm, type);
 	if (ret)
 		return ret;