iwlwifi: work around passive scan issue

Some firmware versions don't behave properly when
passive scanning is requested on radar channels
without enabling active scanning on receiving a
good frame. Work around that issue by asking the
firmware to only enable the active scanning after
receiving a huge number of good frames, a number
that can never be reached during our dwell time.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>

3 files changed, 23 insertions, 7 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-commands.h b/drivers/net/wireless/iwlwifi/iwl-commands.h
index 6383d9f8c9b3..f4e59ae07f8e 100644
--- a/drivers/net/wireless/iwlwifi/iwl-commands.h
+++ b/drivers/net/wireless/iwlwifi/iwl-commands.h
@@ -2621,7 +2621,9 @@ struct iwl_ssid_ie {
 #define PROBE_OPTION_MAX_3945           4
 #define PROBE_OPTION_MAX                20
 #define TX_CMD_LIFE_TIME_INFINITE       cpu_to_le32(0xFFFFFFFF)
-#define IWL_GOOD_CRC_TH                 cpu_to_le16(1)
+#define IWL_GOOD_CRC_TH_DISABLED        0
+#define IWL_GOOD_CRC_TH_DEFAULT         cpu_to_le16(1)
+#define IWL_GOOD_CRC_TH_NEVER           cpu_to_le16(0xffff)
 #define IWL_MAX_SCAN_SIZE 1024
 #define IWL_MAX_CMD_SIZE 4096
 #define IWL_MAX_PROBE_REQUEST           200
diff --git a/drivers/net/wireless/iwlwifi/iwl-scan.c b/drivers/net/wireless/iwlwifi/iwl-scan.c
index 5062f4ebb6a9..2367286eb74d 100644
--- a/drivers/net/wireless/iwlwifi/iwl-scan.c
+++ b/drivers/net/wireless/iwlwifi/iwl-scan.c
@@ -812,16 +812,29 @@ static void iwl_bg_request_scan(struct work_struct *data)
                         rate = IWL_RATE_1M_PLCP;
                         rate_flags = RATE_MCS_CCK_MSK;
                 }
-                scan->good_CRC_th = 0;
+                scan->good_CRC_th = IWL_GOOD_CRC_TH_DISABLED;
         } else if (priv->scan_bands & BIT(IEEE80211_BAND_5GHZ)) {
                 band = IEEE80211_BAND_5GHZ;
                 rate = IWL_RATE_6M_PLCP;
                 /*
-                 * If active scaning is requested but a certain channel
-                 * is marked passive, we can do active scanning if we
-                 * detect transmissions.
+                 * If active scanning is requested but a certain channel is
+                 * marked passive, we can do active scanning if we detect
+                 * transmissions.
+                 *
+                 * There is an issue with some firmware versions that triggers
+                 * a sysassert on a "good CRC threshold" of zero (== disabled),
+                 * on a radar channel even though this means that we should NOT
+                 * send probes.
+                 *
+                 * The "good CRC threshold" is the number of frames that we
+                 * need to receive during our dwell time on a channel before
+                 * sending out probes -- setting this to a huge value will
+                 * mean we never reach it, but at the same time work around
+                 * the aforementioned issue. Thus use IWL_GOOD_CRC_TH_NEVER
+                 * here instead of IWL_GOOD_CRC_TH_DISABLED.
                  */
-                scan->good_CRC_th = is_active ? IWL_GOOD_CRC_TH : 0;
+                scan->good_CRC_th = is_active ? IWL_GOOD_CRC_TH_DEFAULT :
+                                                IWL_GOOD_CRC_TH_NEVER;
 
                 /* Force use of chains B and C (0x6) for scan Rx for 4965
                  * Avoid A (0x1) because of its off-channel reception on A-band.
diff --git a/drivers/net/wireless/iwlwifi/iwl3945-base.c b/drivers/net/wireless/iwlwifi/iwl3945-base.c
index e276f2a4e835..2f47d9332bfc 100644
--- a/drivers/net/wireless/iwlwifi/iwl3945-base.c
+++ b/drivers/net/wireless/iwlwifi/iwl3945-base.c
@@ -2966,7 +2966,8 @@ static void iwl3945_bg_request_scan(struct work_struct *data)
                  * is marked passive, we can do active scanning if we
                  * detect transmissions.
                  */
-                scan->good_CRC_th = is_active ? IWL_GOOD_CRC_TH : 0;
+                scan->good_CRC_th = is_active ? IWL_GOOD_CRC_TH_DEFAULT :
+                                                IWL_GOOD_CRC_TH_DISABLED;
                 band = IEEE80211_BAND_5GHZ;
         } else {
                 IWL_WARN(priv, "Invalid scan band count\n");