[PATCH v4 1/2] netdev: fall back to RSSI polling if SET_CQM fails

James Prestwood
2024-09-03T18:06:59Z

Some drivers fail to set a CQM threshold and report not supported.
Its unclear exactly why but if this happens roaming is effectively
broken.

To work around this enable RSSI polling if -ENOTSUP is returned.
The polling callback has been changed to emit the HIGH/LOW signal
threshold events instead of just the RSSI level index, just as if
a CQM event came from the kernel.
---
src/netdev.c | 158 +++++++++++++++++++++++++++++++++++----------------
1 file changed, 108 insertions(+), 50 deletions(-)

v4:
* Track the command IDs for SET_CQM

diff --git a/src/netdev.c b/src/netdev.c
index 73fbf0c1..14fe41b4 100644
--- a/src/netdev.c
+++ b/src/netdev.c
@@ -133,6 +133,7 @@ struct netdev {
uint32_t get_oci_cmd_id;
uint32_t get_link_cmd_id;
uint32_t power_save_cmd_id;
+ uint32_t set_cqm_cmd_id;
enum netdev_result result;
uint16_t last_code; /* reason or status, depending on result */
struct l_timeout *neighbor_report_timeout;
@@ -190,6 +191,7 @@ struct netdev {
bool retry_auth : 1;
bool in_reassoc : 1;
bool privacy : 1;
+ bool cqm_poll_fallback : 1;
};

struct netdev_preauth_state {
@@ -650,6 +652,47 @@ static void netdev_set_rssi_level_idx(struct netdev *netdev)
netdev->cur_rssi_level_idx = new_level;
}

+static void netdev_cqm_event_rssi_value(struct netdev *netdev, int rssi_val)
+{
+ bool new_rssi_low;
+ uint8_t prev_rssi_level_idx = netdev->cur_rssi_level_idx;
+ int threshold = netdev->frequency > 4000 ?
+ netdev->low_signal_threshold_5ghz :
+ netdev->low_signal_threshold;
+
+ if (!netdev->connected)
+ return;
+
+ if (rssi_val > 127)
+ rssi_val = 127;
+ else if (rssi_val < -127)
+ rssi_val = -127;
+
+ netdev->cur_rssi = rssi_val;
+
+ if (!netdev->event_filter)
+ return;
+
+ new_rssi_low = rssi_val < threshold;
+ if (netdev->cur_rssi_low != new_rssi_low) {
+ int event = new_rssi_low ?
+ NETDEV_EVENT_RSSI_THRESHOLD_LOW :
+ NETDEV_EVENT_RSSI_THRESHOLD_HIGH;
+
+ netdev->cur_rssi_low = new_rssi_low;
+ netdev->event_filter(netdev, event, NULL, netdev->user_data);
+ }
+
+ if (!netdev->rssi_levels_num)
+ return;
+
+ netdev_set_rssi_level_idx(netdev);
+ if (netdev->cur_rssi_level_idx != prev_rssi_level_idx)
+ netdev->event_filter(netdev, NETDEV_EVENT_RSSI_LEVEL_NOTIFY,
+ &netdev->cur_rssi_level_idx,
+ netdev->user_data);
+}
+
static void netdev_rssi_poll_cb(struct l_genl_msg *msg, void *user_data)
{
struct netdev *netdev = user_data;
@@ -686,11 +729,16 @@ static void netdev_rssi_poll_cb(struct l_genl_msg *msg, void *user_data)
netdev->cur_rssi = info.cur_rssi;

/*
- * Note we don't have to handle LOW_SIGNAL_THRESHOLD here. The
- * CQM single threshold RSSI monitoring should work even if the
- * kernel driver doesn't support multiple thresholds. So the
- * polling only handles the client-supplied threshold list.
+ * If the CMD_SET_CQM call failed RSSI polling was started. In this case
+ * we should behave just like its a CQM event and check both the RSSI
+ * level indexes and the HIGH/LOW thresholds.
*/
+ if (netdev->cqm_poll_fallback) {
+ netdev_cqm_event_rssi_value(netdev, info.cur_rssi);
+ goto done;
+ }
+
+ /* Otherwise just update the level notifications, CQM events work */
netdev_set_rssi_level_idx(netdev);
if (netdev->cur_rssi_level_idx != prev_rssi_level_idx)
netdev->event_filter(netdev, NETDEV_EVENT_RSSI_LEVEL_NOTIFY,
@@ -1031,6 +1079,11 @@ static void netdev_free(void *data)
netdev->get_station_cmd_id = 0;
}

+ if (netdev->set_cqm_cmd_id) {
+ l_genl_family_cancel(nl80211, netdev->set_cqm_cmd_id);
+ netdev->set_cqm_cmd_id = 0;
+ }
+
if (netdev->fw_roam_bss)
scan_bss_free(netdev->fw_roam_bss);

@@ -1039,6 +1092,9 @@ static void netdev_free(void *data)
netdev->get_link_cmd_id = 0;
}

+ if (netdev->rssi_poll_timeout)
+ l_timeout_remove(netdev->rssi_poll_timeout);
+
scan_wdev_remove(netdev->wdev_id);

watchlist_destroy(&netdev->station_watches);
@@ -1093,47 +1149,6 @@ static void netdev_cqm_event_rssi_threshold(struct netdev *netdev,
netdev->event_filter(netdev, event, NULL, netdev->user_data);
}

-static void netdev_cqm_event_rssi_value(struct netdev *netdev, int rssi_val)
-{
- bool new_rssi_low;
- uint8_t prev_rssi_level_idx = netdev->cur_rssi_level_idx;
- int threshold = netdev->frequency > 4000 ?
- netdev->low_signal_threshold_5ghz :
- netdev->low_signal_threshold;
-
- if (!netdev->connected)
- return;
-
- if (rssi_val > 127)
- rssi_val = 127;
- else if (rssi_val < -127)
- rssi_val = -127;
-
- netdev->cur_rssi = rssi_val;
-
- if (!netdev->event_filter)
- return;
-
- new_rssi_low = rssi_val < threshold;
- if (netdev->cur_rssi_low != new_rssi_low) {
- int event = new_rssi_low ?
- NETDEV_EVENT_RSSI_THRESHOLD_LOW :
- NETDEV_EVENT_RSSI_THRESHOLD_HIGH;
-
- netdev->cur_rssi_low = new_rssi_low;
- netdev->event_filter(netdev, event, NULL, netdev->user_data);
- }
-
- if (!netdev->rssi_levels_num)
- return;
-
- netdev_set_rssi_level_idx(netdev);
- if (netdev->cur_rssi_level_idx != prev_rssi_level_idx)
- netdev->event_filter(netdev, NETDEV_EVENT_RSSI_LEVEL_NOTIFY,
- &netdev->cur_rssi_level_idx,
- netdev->user_data);
-}
-
static void netdev_cqm_event(struct l_genl_msg *msg, struct netdev *netdev)
{
struct l_genl_attr attr;
@@ -3644,11 +3659,50 @@ static struct l_genl_msg *netdev_build_cmd_cqm_rssi_update(

static void netdev_cmd_set_cqm_cb(struct l_genl_msg *msg, void *user_data)
{
+ struct netdev *netdev = user_data;
int err = l_genl_msg_get_error(msg);
const char *ext_error;

- if (err >= 0)
+ netdev->set_cqm_cmd_id = 0;
+
+ if (err >= 0) {
+ /*
+ * Looking at some driver code it appears that the -ENOTSUP CQM
+ * failure could be transient. Just in case, reset the fallback
+ * flag if CQM happens to start working again.
+ */
+ if (netdev->cqm_poll_fallback) {
+ l_debug("CMD_SET_CQM succeeded, stop polling fallback");
+
+ if (netdev->rssi_poll_timeout) {
+ l_timeout_remove(netdev->rssi_poll_timeout);
+ netdev->rssi_poll_timeout = NULL;
+ }
+
+ netdev->cqm_poll_fallback = false;
+ }
+
+ return;
+ }
+
+ /*
+ * Some drivers enable beacon filtering but also use software CQM which
+ * mac80211 detects and returns -ENOTSUP. There is no way to check this
+ * ahead of time so if we see this start polling in order to get RSSI
+ * updates.
+ */
+ if (err == -ENOTSUP) {
+ l_debug("CMD_SET_CQM not supported, falling back to polling");
+ netdev->cqm_poll_fallback = true;
+
+ if (netdev->rssi_poll_timeout)
+ return;
+
+ netdev->rssi_poll_timeout = l_timeout_create(1,
+ netdev_rssi_poll, netdev, NULL);
+
return;
+ }

ext_error = l_genl_msg_get_extended_error(msg);
l_error("CMD_SET_CQM failed: %s",
@@ -3671,8 +3725,10 @@ static int netdev_cqm_rssi_update(struct netdev *netdev)
if (!msg)
return -EINVAL;

- if (!l_genl_family_send(nl80211, msg, netdev_cmd_set_cqm_cb,
- NULL, NULL)) {
+ netdev->set_cqm_cmd_id = l_genl_family_send(nl80211, msg,
+ netdev_cmd_set_cqm_cb,
+ netdev, NULL);
+ if (!netdev->set_cqm_cmd_id) {
l_genl_msg_unref(msg);
return -EIO;
}
@@ -5309,8 +5365,10 @@ int netdev_set_rssi_report_levels(struct netdev *netdev, const int8_t *levels,
if (!cmd_set_cqm)
return -EINVAL;

- if (!l_genl_family_send(nl80211, cmd_set_cqm, netdev_cmd_set_cqm_cb,
- NULL, NULL)) {
+ netdev->set_cqm_cmd_id = l_genl_family_send(nl80211, cmd_set_cqm,
+ netdev_cmd_set_cqm_cb,
+ netdev, NULL);
+ if (!netdev->set_cqm_cmd_id) {
l_genl_msg_unref(cmd_set_cqm);
return -EIO;
}
--
2.34.1