mac80211: Don't let regulatory make us deaf

When regulatory information changes our HT behavior (e.g,
when we get a country code from the AP we have just associated
with), we should use this information to change the power with
which we transmit, and what channels we transmit.  Sometimes
the channel parameters we derive from regulatory information
contradicts the parameters we used in association.  For example,
we could have associated specifying HT40, but the regulatory
rules we apply may forbid HT40 operation.

In the situation above, we should reconfigure ourselves to
transmit in HT20 only, however it makes no sense for us to
disable receive in HT40, since if we associated with these
parameters, the AP has every reason to expect we can and
will receive packets this way.  The code in mac80211 does
not have the capability of sending the appropriate action
frames to signal a change in HT behaviour so the AP has
no clue we can no longer receive frames encoded this way.
In some broken AP implementations, this can leave us
effectively deaf if the AP never retries in lower HT rates.

This change breaks up the channel_type parameter in the
ieee80211_enable_ht function into a separate receive and
transmit part.  It honors the channel flags set by regulatory
in order to configure the rate control algorithm, but uses
the capability flags to configure the channel on the radio,
since these were used in association to set the AP's transmit
rate.

Signed-off-by: Paul Stewart <pstew@chromium.org>
Cc: Sam Leffler <sleffler@chromium.org>
Cc: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Luis R Rodriguez <mcgrof@frijolero.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/net/mac80211/chan.c b/net/mac80211/chan.c
index d1f7abddb182..e00ce8c3e28e 100644
--- a/net/mac80211/chan.c
+++ b/net/mac80211/chan.c
@@ -3,6 +3,7 @@
  */
 
 #include <linux/nl80211.h>
+#include <net/cfg80211.h>
 #include "ieee80211_i.h"
 
 static enum ieee80211_chan_mode
@@ -134,3 +135,29 @@ bool ieee80211_set_channel_type(struct ieee80211_local *local,
 
         return result;
 }
+
+/*
+ * ieee80211_get_tx_channel_type returns the channel type we should
+ * use for packet transmission, given the channel capability and
+ * whatever regulatory flags we have been given.
+ */
+enum nl80211_channel_type ieee80211_get_tx_channel_type(
+                                struct ieee80211_local *local,
+                                enum nl80211_channel_type channel_type)
+{
+        switch (channel_type) {
+        case NL80211_CHAN_HT40PLUS:
+                if (local->hw.conf.channel->flags &
+                                IEEE80211_CHAN_NO_HT40PLUS)
+                        return NL80211_CHAN_HT20;
+                break;
+        case NL80211_CHAN_HT40MINUS:
+                if (local->hw.conf.channel->flags &
+                                IEEE80211_CHAN_NO_HT40MINUS)
+                        return NL80211_CHAN_HT20;
+                break;
+        default:
+                break;
+        }
+        return channel_type;
+}