mac80211: add fixed_rate management to minstrel rc

Add the capability to use a fixed modulation rate to minstrel rate controller

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rc80211_minstrel.c

@@ -203,6 +203,15 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 	memcpy(mi->max_tp_rate, tmp_tp_rate, sizeof(mi->max_tp_rate));
 	mi->max_prob_rate = tmp_prob_rate;
 
+#ifdef CONFIG_MAC80211_DEBUGFS
+	/* use fixed index if set */
+	if (mp->fixed_rate_idx != -1) {
+		mi->max_tp_rate[0] = mp->fixed_rate_idx;
+		mi->max_tp_rate[1] = mp->fixed_rate_idx;
+		mi->max_prob_rate = mp->fixed_rate_idx;
+	}
+#endif
+
 	/* Reset update timer */
 	mi->stats_update = jiffies;
 
@@ -310,6 +319,11 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
 	/* increase sum packet counter */
 	mi->packet_count++;
 
+#ifdef CONFIG_MAC80211_DEBUGFS
+	if (mp->fixed_rate_idx != -1)
+		return;
+#endif
+
 	delta = (mi->packet_count * sampling_ratio / 100) -
 			(mi->sample_count + mi->sample_deferred / 2);