mac80211_hwsim: fix tsf adjustment

Make hwsim TSF offset adjustments cumulative and relative
to the fake PHY TSF. Now adding 1000us, then adding -1000us
doesn't result in a tsf_offset of -1000. Also the beacon
timestamp can now correctly be expressed as (tsf +
data->tsf_offset), which will be done in a later patch.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/mac80211_hwsim.c

@@ -361,7 +361,7 @@ struct mac80211_hwsim_data {
 	int power_level;
 
 	/* difference between this hw's clock and the real clock, in usecs */
-	u64 tsf_offset;
+	s64 tsf_offset;
 };
 
 
@@ -427,9 +427,10 @@ static void mac80211_hwsim_set_tsf(struct ieee80211_hw *hw,
 		struct ieee80211_vif *vif, u64 tsf)
 {
 	struct mac80211_hwsim_data *data = hw->priv;
-	struct timeval tv = ktime_to_timeval(ktime_get_real());
-	u64 now = tv.tv_sec * USEC_PER_SEC + tv.tv_usec;
-	data->tsf_offset = tsf - now;
+	u64 now = mac80211_hwsim_get_tsf(hw, vif);
+	s64 delta = tsf - now;
+
+	data->tsf_offset += delta;
 }
 
 static void mac80211_hwsim_monitor_rx(struct ieee80211_hw *hw,