minstrel_ht: fixed rate mode through debugfs

Found several threads about fixed rate mode in minstrel_ht for test
environments, but no patches for it.

This patch provides such a mode through debugfs.
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rc80211_minstrel.c

@@ -532,12 +532,21 @@ minstrel_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
 	mp->hw = hw;
 	mp->update_interval = 100;
 
+#ifdef CONFIG_MAC80211_DEBUGFS
+	mp->fixed_rate_idx = (u32) -1;
+	mp->dbg_fixed_rate = debugfs_create_u32("fixed_rate_idx",
+			S_IRUGO | S_IWUGO, debugfsdir, &mp->fixed_rate_idx);
+#endif
+
 	return mp;
 }
 
 static void
 minstrel_free(void *priv)
 {
+#ifdef CONFIG_MAC80211_DEBUGFS
+	debugfs_remove(((struct minstrel_priv *)priv)->dbg_fixed_rate);
+#endif
 	kfree(priv);
 }
 

net/mac80211/rc80211_minstrel.h

@@ -78,6 +78,18 @@ struct minstrel_priv {
 	unsigned int update_interval;
 	unsigned int lookaround_rate;
 	unsigned int lookaround_rate_mrr;
+
+#ifdef CONFIG_MAC80211_DEBUGFS
+	/*
+	 * enable fixed rate processing per RC
+	 *   - write static index to debugfs:ieee80211/phyX/rc/fixed_rate_idx
+	 *   - write -1 to enable RC processing again
+	 *   - setting will be applied on next update
+	 */
+	u32 fixed_rate_idx;
+	struct dentry *dbg_fixed_rate;
+#endif
+
 };
 
 struct minstrel_debugfs_info {

net/mac80211/rc80211_minstrel_ht.c

@@ -609,6 +609,13 @@ minstrel_ht_get_rate(void *priv, struct ieee80211_sta *sta, void *priv_sta,
 
 	info->flags |= mi->tx_flags;
 	sample_idx = minstrel_get_sample_rate(mp, mi);
+
+#ifdef CONFIG_MAC80211_DEBUGFS
+	/* use fixed index if set */
+	if (mp->fixed_rate_idx != -1)
+		sample_idx = mp->fixed_rate_idx;
+#endif
+
 	if (sample_idx >= 0) {
 		sample = true;
 		minstrel_ht_set_rate(mp, mi, &ar[0], sample_idx,