mac80211: stop toggling IEEE80211_HT_CAP_SUP_WIDTH_20_40

For VHT, many more bandwidth changes are possible. As a first
step, stop toggling the IEEE80211_HT_CAP_SUP_WIDTH_20_40 flag
in the HT capabilities and instead introduce a bandwidth field
indicating the currently usable bandwidth to transmit to the
station. Of course, make all drivers use it.

To achieve this, make ieee80211_ht_cap_ie_to_sta_ht_cap() get
the station as an argument, rather than the new capabilities,
so it can set up the new bandwidth field.

If the station is a VHT station and VHT bandwidth is in use,
also set the bandwidth accordingly.

Doing this allows us to get rid of the supports_40mhz flag as
the HT capabilities now reflect the true capability instead of
the current setting.

While at it, also fix ieee80211_ht_cap_ie_to_sta_ht_cap() to not
ignore HT cap overrides when MCS TX isn't supported (not that it
really happens...)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index 6e35dcd..6176c71 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -848,8 +848,6 @@
 		IEEE80211_HT_CAP_SM_PS_SHIFT;
 
 	for (i = 0; i < ARRAY_SIZE(mi->groups); i++) {
-		u16 req = 0;
-
 		mi->groups[i].supported = 0;
 		if (i == MINSTREL_CCK_GROUP) {
 			minstrel_ht_update_cck(mp, mi, sband, sta);
@@ -857,16 +855,17 @@
 		}
 
 		if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_SHORT_GI) {
-			if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
-				req |= IEEE80211_HT_CAP_SGI_40;
-			else
-				req |= IEEE80211_HT_CAP_SGI_20;
+			if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH) {
+				if (!(sta_cap & IEEE80211_HT_CAP_SGI_40))
+					continue;
+			} else {
+				if (!(sta_cap & IEEE80211_HT_CAP_SGI_20))
+					continue;
+			}
 		}
 
-		if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
-			req |= IEEE80211_HT_CAP_SUP_WIDTH_20_40;
-
-		if ((sta_cap & req) != req)
+		if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH &&
+		    sta->bandwidth < IEEE80211_STA_RX_BW_40)
 			continue;
 
 		/* Mark MCS > 7 as unsupported if STA is in static SMPS mode */