mac80211: allow disabling 40MHz on 2.4GHz

In some situations it is required that a system be
configured with no support for 40 MHz channels in
the 2.4 GHz band. Rather than imposing any such
restrictions on everybody, allow configuration a
system like that with a module parameter. It is
writable at runtime but only takes effect at the
time of the next association.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

4 files changed, 25 insertions, 3 deletions

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index e63aecbddfbe..6fb3f7181536 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -881,6 +881,8 @@ void ieee80211_bss_info_change_notify(struct ieee80211_sub_if_data *sdata,
 void ieee80211_configure_filter(struct ieee80211_local *local);
 u32 ieee80211_reset_erp_info(struct ieee80211_sub_if_data *sdata);
 
+extern bool ieee80211_disable_40mhz_24ghz;
+
 /* STA code */
 void ieee80211_sta_setup_sdata(struct ieee80211_sub_if_data *sdata);
 int ieee80211_mgd_auth(struct ieee80211_sub_if_data *sdata,
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index e1293e8ed83a..25f52098b636 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -33,6 +33,12 @@
 #include "cfg.h"
 #include "debugfs.h"
 
+
+bool ieee80211_disable_40mhz_24ghz;
+module_param(ieee80211_disable_40mhz_24ghz, bool, 0644);
+MODULE_PARM_DESC(ieee80211_disable_40mhz_24ghz,
+                 "Disable 40MHz support in the 2.4GHz band");
+
 void ieee80211_configure_filter(struct ieee80211_local *local)
 {
         u64 mc;
diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 0a762a9ba4df..a7472c979c63 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -400,6 +400,12 @@ static void ieee80211_send_assoc(struct ieee80211_sub_if_data *sdata,
 
                 /* determine capability flags */
 
+                if (ieee80211_disable_40mhz_24ghz &&
+                    sband->band == IEEE80211_BAND_2GHZ) {
+                        cap &= ~IEEE80211_HT_CAP_SUP_WIDTH_20_40;
+                        cap &= ~IEEE80211_HT_CAP_SGI_40;
+                }
+
                 switch (ht_info->ht_param & IEEE80211_HT_PARAM_CHA_SEC_OFFSET) {
                 case IEEE80211_HT_PARAM_CHA_SEC_ABOVE:
                         if (flags & IEEE80211_CHAN_NO_HT40PLUS) {
diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index 086ef6257b4b..acb6626ad0a4 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -908,16 +908,24 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
         }
 
         if (sband->ht_cap.ht_supported) {
-                __le16 tmp = cpu_to_le16(sband->ht_cap.cap);
+                u16 cap = sband->ht_cap.cap;
+                __le16 tmp;
+
+                if (ieee80211_disable_40mhz_24ghz &&
+                    sband->band == IEEE80211_BAND_2GHZ) {
+                        cap &= ~IEEE80211_HT_CAP_SUP_WIDTH_20_40;
+                        cap &= ~IEEE80211_HT_CAP_SGI_40;
+                }
 
                 *pos++ = WLAN_EID_HT_CAPABILITY;
                 *pos++ = sizeof(struct ieee80211_ht_cap);
                 memset(pos, 0, sizeof(struct ieee80211_ht_cap));
+                tmp = cpu_to_le16(cap);
                 memcpy(pos, &tmp, sizeof(u16));
                 pos += sizeof(u16);
-                /* TODO: needs a define here for << 2 */
                 *pos++ = sband->ht_cap.ampdu_factor |
-                         (sband->ht_cap.ampdu_density << 2);
+                         (sband->ht_cap.ampdu_density <<
+                                IEEE80211_HT_AMPDU_PARM_DENSITY_SHIFT);
                 memcpy(pos, &sband->ht_cap.mcs, sizeof(sband->ht_cap.mcs));
                 pos += sizeof(sband->ht_cap.mcs);
                 pos += 2 + 4 + 1; /* ext info, BF cap, antsel */