cfg80211/mac80211: use reduced txpower for 5 and 10 MHz

Some regulations (like germany, but also FCC) express their transmission
power limit in dBm/MHz or mW/MHz. To cope with that and be on the safe
side, reduce the maximum power to half (10 MHz) or quarter (5 MHz)
when operating on these reduced bandwidth channels.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

1 files changed, 27 insertions, 0 deletions

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 88f15631701a..aeaf6dff6e05 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -461,6 +461,33 @@ ieee80211_chandef_rate_flags(struct cfg80211_chan_def *chandef)
 }
 
 /**
+ * ieee80211_chandef_max_power - maximum transmission power for the chandef
+ *
+ * In some regulations, the transmit power may depend on the configured channel
+ * bandwidth which may be defined as dBm/MHz. This function returns the actual
+ * max_power for non-standard (20 MHz) channels.
+ *
+ * @chandef: channel definition for the channel
+ *
+ * Returns: maximum allowed transmission power in dBm for the chandef
+ */
+static inline int
+ieee80211_chandef_max_power(struct cfg80211_chan_def *chandef)
+{
+        switch (chandef->width) {
+        case NL80211_CHAN_WIDTH_5:
+                return min(chandef->chan->max_reg_power - 6,
+                           chandef->chan->max_power);
+        case NL80211_CHAN_WIDTH_10:
+                return min(chandef->chan->max_reg_power - 3,
+                           chandef->chan->max_power);
+        default:
+                break;
+        }
+        return chandef->chan->max_power;
+}
+
+/**
  * enum survey_info_flags - survey information flags
  *
  * @SURVEY_INFO_NOISE_DBM: noise (in dBm) was filled in