wireless: fix enabling channel 12 for custom regulatory domain

Commit e33e2241 ("Revert "cfg80211: Use 5MHz bandwidth by
default when checking usable channels"") fixed a broken
regulatory (leaving channel 12 open for AP where not permitted).
Apply a similar fix to custom regulatory domain processing.
Signed-off-by: Cathy Luo <xiaohua.luo@nxp.com>
Signed-off-by: Ganapathi Bhat <ganapathi.bhat@nxp.com>
Link: https://lore.kernel.org/r/1576836859-8945-1-git-send-email-ganapathi.bhat@nxp.com
[reword commit message, fix coding style, add a comment]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/reg.c

@@ -2261,14 +2261,15 @@ static void update_all_wiphy_regulatory(enum nl80211_reg_initiator initiator)
 
 static void handle_channel_custom(struct wiphy *wiphy,
 				  struct ieee80211_channel *chan,
-				  const struct ieee80211_regdomain *regd)
+				  const struct ieee80211_regdomain *regd,
+				  u32 min_bw)
 {
 	u32 bw_flags = 0;
 	const struct ieee80211_reg_rule *reg_rule = NULL;
 	const struct ieee80211_power_rule *power_rule = NULL;
 	u32 bw;
 
-	for (bw = MHZ_TO_KHZ(20); bw >= MHZ_TO_KHZ(5); bw = bw / 2) {
+	for (bw = MHZ_TO_KHZ(20); bw >= min_bw; bw = bw / 2) {
 		reg_rule = freq_reg_info_regd(MHZ_TO_KHZ(chan->center_freq),
 					      regd, bw);
 		if (!IS_ERR(reg_rule))
@@ -2324,8 +2325,14 @@ static void handle_band_custom(struct wiphy *wiphy,
 	if (!sband)
 		return;
 
+	/*
+	 * We currently assume that you always want at least 20 MHz,
+	 * otherwise channel 12 might get enabled if this rule is
+	 * compatible to US, which permits 2402 - 2472 MHz.
+	 */
 	for (i = 0; i < sband->n_channels; i++)
-		handle_channel_custom(wiphy, &sband->channels[i], regd);
+		handle_channel_custom(wiphy, &sband->channels[i], regd,
+				      MHZ_TO_KHZ(20));
 }
 
 /* Used by drivers prior to wiphy registration */