mac80211: add max channel calculation utility function

The utility function has no uses yet. It is aimed
at future chanctx reservation management and
channel switching.
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ieee80211_i.h

@@ -1822,6 +1822,7 @@ int ieee80211_check_combinations(struct ieee80211_sub_if_data *sdata,
 				 const struct cfg80211_chan_def *chandef,
 				 enum ieee80211_chanctx_mode chanmode,
 				 u8 radar_detect);
+int ieee80211_max_num_channels(struct ieee80211_local *local);
 
 #ifdef CONFIG_MAC80211_NOINLINE
 #define debug_noinline noinline

net/mac80211/util.c

@@ -2873,3 +2873,45 @@ int ieee80211_check_combinations(struct ieee80211_sub_if_data *sdata,
 					   num_different_channels,
 					   radar_detect, num);
 }
+
+static void
+ieee80211_iter_max_chans(const struct ieee80211_iface_combination *c,
+			 void *data)
+{
+	u32 *max_num_different_channels = data;
+
+	*max_num_different_channels = max(*max_num_different_channels,
+					  c->num_different_channels);
+}
+
+int ieee80211_max_num_channels(struct ieee80211_local *local)
+{
+	struct ieee80211_sub_if_data *sdata;
+	int num[NUM_NL80211_IFTYPES] = {};
+	struct ieee80211_chanctx *ctx;
+	int num_different_channels = 0;
+	u8 radar_detect = 0;
+	u32 max_num_different_channels = 1;
+	int err;
+
+	lockdep_assert_held(&local->chanctx_mtx);
+
+	list_for_each_entry(ctx, &local->chanctx_list, list) {
+		num_different_channels++;
+
+		if (ctx->conf.radar_enabled)
+			radar_detect |= BIT(ctx->conf.def.width);
+	}
+
+	list_for_each_entry_rcu(sdata, &local->interfaces, list)
+		num[sdata->wdev.iftype]++;
+
+	err = cfg80211_iter_combinations(local->hw.wiphy,
+					 num_different_channels, radar_detect,
+					 num, ieee80211_iter_max_chans,
+					 &max_num_different_channels);
+	if (err < 0)
+		return err;
+
+	return max_num_different_channels;
+}