wpa_supplicant: Allow user to disable short guard interval (SGI)

Requires Linux kernel patch to make the SGI-20 properly disabled. SGI-40
will already work since Linux 3.4 or so.

Signed-hostap: Ben Greear <greearb@candelatech.com>
Signed-off-by: Ben Greear <greearb@candelatech.com>

wpa_supplicant/config.c

@@ -1637,6 +1637,7 @@ static const struct parse_data ssid_fields[] = {
 #ifdef CONFIG_HT_OVERRIDES
 	{ INT_RANGE(disable_ht, 0, 1) },
 	{ INT_RANGE(disable_ht40, -1, 1) },
+	{ INT_RANGE(disable_sgi, 0, 1) },
 	{ INT_RANGE(disable_max_amsdu, -1, 1) },
 	{ INT_RANGE(ampdu_factor, -1, 3) },
 	{ INT_RANGE(ampdu_density, -1, 7) },
@@ -2038,6 +2039,7 @@ void wpa_config_set_network_defaults(struct wpa_ssid *ssid)
 #ifdef CONFIG_HT_OVERRIDES
 	ssid->disable_ht = DEFAULT_DISABLE_HT;
 	ssid->disable_ht40 = DEFAULT_DISABLE_HT40;
+	ssid->disable_sgi = DEFAULT_DISABLE_SGI;
 	ssid->disable_max_amsdu = DEFAULT_DISABLE_MAX_AMSDU;
 	ssid->ampdu_factor = DEFAULT_AMPDU_FACTOR;
 	ssid->ampdu_density = DEFAULT_AMPDU_DENSITY;

wpa_supplicant/config_ssid.h

@@ -28,6 +28,7 @@
 #define DEFAULT_BG_SCAN_PERIOD -1
 #define DEFAULT_DISABLE_HT 0
 #define DEFAULT_DISABLE_HT40 0
+#define DEFAULT_DISABLE_SGI 0
 #define DEFAULT_DISABLE_MAX_AMSDU -1 /* no change */
 #define DEFAULT_AMPDU_FACTOR -1 /* no change */
 #define DEFAULT_AMPDU_DENSITY -1 /* no change */
@@ -494,6 +495,14 @@ struct wpa_ssid {
 	 */
 	int disable_ht40;
 
+	/**
+	 * disable_sgi - Disable SGI (Short Guard Interval) for this network
+	 *
+	 * By default, use it if it is available, but this can be configured
+	 * to 1 to have it disabled.
+	 */
+	int disable_sgi;
+
 	/**
 	 * disable_max_amsdu - Disable MAX A-MSDU
 	 *

wpa_supplicant/wpa_supplicant.c

@@ -2579,6 +2579,28 @@ static int wpa_set_disable_ht40(struct wpa_supplicant *wpa_s,
 }
 
 
+static int wpa_set_disable_sgi(struct wpa_supplicant *wpa_s,
+			       struct ieee80211_ht_capabilities *htcaps,
+			       struct ieee80211_ht_capabilities *htcaps_mask,
+			       int disabled)
+{
+	/* Masking these out disables SGI */
+	u16 msk = host_to_le16(HT_CAP_INFO_SHORT_GI20MHZ |
+			       HT_CAP_INFO_SHORT_GI40MHZ);
+
+	wpa_msg(wpa_s, MSG_DEBUG, "set_disable_sgi: %d", disabled);
+
+	if (disabled)
+		htcaps->ht_capabilities_info &= ~msk;
+	else
+		htcaps->ht_capabilities_info |= msk;
+
+	htcaps_mask->ht_capabilities_info |= msk;
+
+	return 0;
+}
+
+
 void wpa_supplicant_apply_ht_overrides(
 	struct wpa_supplicant *wpa_s, struct wpa_ssid *ssid,
 	struct wpa_driver_associate_params *params)
@@ -2601,6 +2623,7 @@ void wpa_supplicant_apply_ht_overrides(
 	wpa_set_ampdu_factor(wpa_s, htcaps, htcaps_mask, ssid->ampdu_factor);
 	wpa_set_ampdu_density(wpa_s, htcaps, htcaps_mask, ssid->ampdu_density);
 	wpa_set_disable_ht40(wpa_s, htcaps, htcaps_mask, ssid->disable_ht40);
+	wpa_set_disable_sgi(wpa_s, htcaps, htcaps_mask, ssid->disable_sgi);
 }
 
 #endif /* CONFIG_HT_OVERRIDES */