cfg80211: document sched_scan_stop synchronous behaviour

Due to userspace assumptions, the sched_scan_stop operation must
be synchronous, i.e. once it returns a new scheduled scan must be
able to start immediately. Document this in the API.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -2206,7 +2206,12 @@ struct cfg80211_qos_map {
  * @set_cqm_txe_config: Configure connection quality monitor TX error
  *	thresholds.
  * @sched_scan_start: Tell the driver to start a scheduled scan.
- * @sched_scan_stop: Tell the driver to stop an ongoing scheduled scan.
+ * @sched_scan_stop: Tell the driver to stop an ongoing scheduled scan. This
+ *	call must stop the scheduled scan and be ready for starting a new one
+ *	before it returns, i.e. @sched_scan_start may be called immediately
+ *	after that again and should not fail in that case. The driver should
+ *	not call cfg80211_sched_scan_stopped() for a requested stop (when this
+ *	method returns 0.)
  *
  * @mgmt_frame_register: Notify driver that a management frame type was
  *	registered. Note that this callback may not sleep, and cannot run

include/uapi/linux/nl80211.h

@@ -303,8 +303,9 @@
  *	passed, all channels allowed for the current regulatory domain
  *	are used.  Extra IEs can also be passed from the userspace by
  *	using the %NL80211_ATTR_IE attribute.
- * @NL80211_CMD_STOP_SCHED_SCAN: stop a scheduled scan.  Returns -ENOENT
- *	if scheduled scan is not running.
+ * @NL80211_CMD_STOP_SCHED_SCAN: stop a scheduled scan. Returns -ENOENT if
+ *	scheduled scan is not running. The caller may assume that as soon
+ *	as the call returns, it is safe to start a new scheduled scan again.
  * @NL80211_CMD_SCHED_SCAN_RESULTS: indicates that there are scheduled scan
  *	results available.
  * @NL80211_CMD_SCHED_SCAN_STOPPED: indicates that the scheduled scan has