mac80211: only bother printing highest data rate on debugfs if its set

IEEE-802.11n spec says the RX highest data rate field does
not specify the highest supported RX data rate if its not set.
Ignore it if not set then. Refer to section 7.3.56.4

Cc: johannes@sipsolutions.net
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/linux/ieee80211.h

@@ -775,7 +775,10 @@ struct ieee80211_bar {
 /**
  * struct ieee80211_mcs_info - MCS information
  * @rx_mask: RX mask
- * @rx_highest: highest supported RX rate
+ * @rx_highest: highest supported RX rate. If set represents
+ *	the highest supported RX data rate in units of 1 Mbps.
+ *	If this field is 0 this value should not be used to
+ *	consider the highest RX data rate supported.
  * @tx_params: TX parameters
  */
 struct ieee80211_mcs_info {

net/mac80211/debugfs_sta.c

@@ -218,11 +218,19 @@ static ssize_t sta_ht_capa_read(struct file *file, char __user *userbuf,
 		p += scnprintf(p, sizeof(buf)+buf-p, "ampdu factor/density: %d/%d\n",
 				htc->ampdu_factor, htc->ampdu_density);
 		p += scnprintf(p, sizeof(buf)+buf-p, "MCS mask:");
+
 		for (i = 0; i < IEEE80211_HT_MCS_MASK_LEN; i++)
 			p += scnprintf(p, sizeof(buf)+buf-p, " %.2x",
 					htc->mcs.rx_mask[i]);
-		p += scnprintf(p, sizeof(buf)+buf-p, "\nMCS rx highest: %d\n",
-				le16_to_cpu(htc->mcs.rx_highest));
+		p += scnprintf(p, sizeof(buf)+buf-p, "\n");
+
+		/* If not set this is meaningless */
+		if (le16_to_cpu(htc->mcs.rx_highest)) {
+			p += scnprintf(p, sizeof(buf)+buf-p,
+				       "MCS rx highest: %d Mbps\n",
+				       le16_to_cpu(htc->mcs.rx_highest));
+		}
+
 		p += scnprintf(p, sizeof(buf)+buf-p, "MCS tx params: %x\n",
 				htc->mcs.tx_params);
 	}