From 420852ff044c804a6487ccc060f85c12bbdaac31 Mon Sep 17 00:00:00 2001
From: Seevalamuthu Mariappan <seevalam@codeaurora.org>
Date: Thu, 1 Jul 2021 10:15:29 +0530
Subject: [PATCH] hostap: Avoid selecting UNII-1 channel after DFS switch

Avoid UNII-1 band channel from getting selected after DFS when primary
channel is UNII-2 band with 80Mhz configuration.

To enable this, 'skip_unii1_dfs_switch' config should be enabled
in hostapd config.

Signed-off-by: Seevalamuthu Mariappan <seevalam@codeaurora.org>
---
 hostapd/config_file.c |  2 ++
 src/ap/ap_config.h    |  1 +
 src/ap/dfs.c          | 25 +++++++++++++++++++++++++
 3 files changed, 28 insertions(+)

--- a/hostapd/config_file.c
+++ b/hostapd/config_file.c
@@ -3377,6 +3377,8 @@ static int hostapd_config_fill(struct ho
 		conf->require_ht = atoi(pos);
 	} else if (os_strcmp(buf, "obss_interval") == 0) {
 		conf->obss_interval = atoi(pos);
+	} else if (os_strcmp(buf, "skip_unii1_dfs_switch") == 0) {
+		conf->skip_unii1_dfs_switch = atoi(pos);
 #ifdef CONFIG_IEEE80211AC
 	} else if (os_strcmp(buf, "ieee80211ac") == 0) {
 		conf->ieee80211ac = atoi(pos);
--- a/src/ap/ap_config.h
+++ b/src/ap/ap_config.h
@@ -1045,6 +1045,7 @@ struct hostapd_config {
 
 	/* Use driver-generated interface addresses when adding multiple BSSs */
 	u8 use_driver_iface_addr;
+	u8 skip_unii1_dfs_switch;
 
 #ifdef CONFIG_FST
 	struct fst_iface_cfg fst_cfg;
--- a/src/ap/dfs.c
+++ b/src/ap/dfs.c
@@ -199,6 +199,64 @@ static int is_in_chanlist(struct hostapd
 	return freq_range_list_includes(&iface->conf->acs_ch_list, chan->chan);
 }
 
+#define HOSTAPD_DFS_UNII2_CHANNELS(chan) (chan >= 52 && chan <= 64)
+
+static bool is_skip_unii1_dfs_switch_applicable(struct hostapd_iface *iface,
+				  		struct hostapd_channel_data *chan)
+{
+	if (!iface->conf->skip_unii1_dfs_switch)
+		return false;
+
+	/* skip if the selected channel is 52/56/60/64 */
+	if (HOSTAPD_DFS_UNII2_CHANNELS(iface->conf->channel) &&
+	    HOSTAPD_DFS_UNII2_CHANNELS(chan->chan))
+		return true;
+
+	/* Skip below mentioned adjacent channels if one of the following
+	 * conditions is true
+	 * i) The primary channel of the AP is 52/56/60/64 in 80MHz mode and
+	 * moves to adjacent channel 36/44/48 in 80MHz
+	 * ii) The primary channel of the AP is 36/44/48/52/56/60/64 in 160MHz
+	 * and moves to 36/44/48 in 80MHz mode
+	 * iii) The primary channel of the AP is 52/56/60/64 in 20MHz or 40MHz mode
+	 * and moves to the adjacent channels 40/44/48 in 20MHz mode or 36/40/44/48
+	 * in 40MHz mode
+	 */
+	switch(hostapd_get_oper_chwidth(iface->conf))
+	{
+		case CHANWIDTH_160MHZ:
+			if ((iface->conf->channel >= 36) &&
+			    (iface->conf->channel <= 64) &&
+			    (iface->conf->channel != 40) &&
+			    (chan->chan >= 36) && (chan->chan <= 48) &&
+			    (chan->chan != 40))
+				return true;
+			break;
+		case CHANWIDTH_80MHZ:
+			if ((iface->conf->channel >= 52) &&
+			    (iface->conf->channel <= 64) &&
+			    (chan->chan >= 36) && (chan->chan <= 48) &&
+			    (chan->chan != 40))
+				return true;
+			break;
+		case CHANWIDTH_USE_HT:
+			if ((iface->conf->channel >= 52) &&
+			    (iface->conf->channel <= 64)) {
+				if (iface->conf->secondary_channel) {
+					if ((chan->chan >= 36) && (chan->chan <= 48))
+						return true;
+				} else {
+					if ((chan->chan >= 40) && (chan->chan <= 48))
+						return true;
+				}
+			}
+			break;
+		default:
+			break;
+	}
+	   
+	return false;
+}
 
 /*
  * The function assumes HT40+ operation.
@@ -248,6 +306,13 @@ static int dfs_find_channel(struct hosta
 			continue;
 		}
 
+		if (is_skip_unii1_dfs_switch_applicable(iface, chan)) {
+			wpa_printf(MSG_DEBUG,
+				   "DFS: skip_unii1_dfs_switch enabled, skip adjacent channel: %d (%d)",
+				   chan->freq, chan->chan);
+			continue;
+		}
+
 		if (chan->max_tx_power < iface->conf->min_tx_power)
 			continue;
 
@@ -963,8 +1028,15 @@ dfs_downgrade_bandwidth(struct hostapd_i
 			int oper_chwidth;
 
 			oper_chwidth = hostapd_get_oper_chwidth(iface->conf);
-			if (oper_chwidth == CHANWIDTH_USE_HT)
-				break;
+			if (oper_chwidth == CHANWIDTH_USE_HT) {
+				/* try finding 20MHz channels if skip_unii1_dfs_switch is enabled */
+				if (!iface->conf->skip_unii1_dfs_switch ||
+				    !iface->conf->secondary_channel)
+					break;
+				iface->conf->secondary_channel = 0;
+				*skip_radar = 1;
+				continue;
+			}
 			*skip_radar = 1;
 			hostapd_set_oper_chwidth(iface->conf, oper_chwidth - 1);
 		}