| Message ID | 20210908133019.2408092-2-bryan.odonoghue@linaro.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Kalle Valo |
| Headers | show |
| Series | wcn36xx: Two one line fixes for Antenna Diveristy Switching | expand |
On 9/8/21 6:30 AM, Bryan O'Donoghue wrote: > We have been tracking a strange bug with Antenna Diversity Switching (ADS) > on wcn3680b for a while. > > ADS is configured like this: > A. Via a firmware configuration table baked into the firmware binary. in the NV, not the firmware binary > 1. Defines if ADS is enabled. > 2. Defines which GPIOs are connected to which antenna enable pin. > 3. Defines which antenna/GPIO is primary and which is secondary. > > B. WCN36XX_CFG_VAL(ANTENNA_DIVERSITY, N) > N is a bitmask of available antenna. > > Setting N to 3 indicates a bitmask of enabled antenna (1 | 2). > > Obviously then we can set N to 1 or N to 2 to fix to a particular > antenna and disable antenna diversity. > > C. WCN36XX_CFG_VAL(ASD_PROBE_INTERVAL, XX) > XX is the number of beacons between each antenna RSSI check. > Setting this value to 50 means, every 50 received beacons, run the > ADS algorithm. > > D. WCN36XX_CFG_VAL(ASD_TRIGGER_THRESHOLD, YY) > YY is a two's complement integer which specifies the RSSI decibel > threshold below which ADS will run. > We default to -60db here, meaning a measured RSSI <= -60db will > trigger an ADS probe. > > E. WCN36XX_CFG_VAL(ASD_RTT_RSSI_HYST_THRESHOLD, Z) > Z is a hysteresis value, indicating a delta which the RSSI must > exceed for the antenna switch to be valid. > > For example if HYST_THRESHOLD == 3 AntennaId1-RSSI == -60db and > AntennaId-2-RSSI == -58db then firmware will not switch antenna. > The threshold needs to be -57db or better to satisfy the criteria. Maybe also worth mentioning there's a feat_cap for ANTENNA_DIVERSITY_SELECTION, although from what we saw FW doesn't actually check it. > > ADS works like this: > > A. Every XX beacons the firmware switches to or remains on the primary > antenna. > > B. The firmware then sends a Request-To-Send (RTS) packet to the AP. > > C. The firmware waits for a Clear-To-Send (CTS) response from the AP. > > D. The firmware then notes the received RSSI on the CTS packet. > > E. The firmware then repeats steps A-D on the secondary antenna. > > F. Subsequently if the measured RSSI on the primary or secondary > antenna is better than ASD_TRIGGER_THRESHOLD + better than the active antenna's RSSI + > ASD_RTT_RSSI_HYST_THRESHOLD then that antenna becomes the active > antenna. > > G. If RSSI rises past ASD_TRIGGER_THRESHOLD then ADS doesn't run at > all even if there is a substantially better RSSI on the other > antenna. > > What we have been observing is that the RTS packet is being sent but the > MAC address is a byte-swapped version of the target MAC. The ADS/RTS MAC is > corrupted only when the link is encrypted, if the AP is open the RTS MAC is > correct. Similarly if we configure the firmware to an RTS/CTS sequence for > regular data - the transmitted RTS MAC is correctly formatted. > > Internally the wcn36xx firmware uses the indexes in the SMD commands to > populate and extract data from specific entries in an STA lookup table. The > AP's MAC appears a number of times in different indexes within this lookup > table, so the MAC address extracted for the data-transmit RTS and the MAC > address extracted for the ADS/RTS packet are not the same STA table index. > > Our analysis indicates the relevant firmware STA table index is > "bssSelfStaIdx". > > There is an STA populate function responsible for formatting the MAC > address of the bssSelfStaIdx including byte-swapping the MAC address. > > Its clear then that the required STA populate command did not run for > bssSelfStaIdx. > > So taking a look at the sequence of SMD commands sent to the firmware we > see the following downstream when moving from an unencrypted to encrypted > BSS setup. > > - WLAN_HAL_CONFIG_BSS_REQ > - WLAN_HAL_CONFIG_STA_REQ > - WLAN_HAL_SET_STAKEY_REQ > > Upstream in wcn36xx we have > > - WLAN_HAL_CONFIG_BSS_REQ > - WLAN_HAL_SET_STAKEY_REQ > > The solution then is to add the missing WLAN_HAL_CONFIG_STA_REQ between > WLAN_HAL_CONFIG_BSS_REQ and WLAN_HAL_SET_STAKEY_REQ. > > No surprise WLAN_HAL_CONFIG_STA_REQ is the routine responsible for > populating the STA lookup table in the firmware and once done the MAC sent > by the ADS routine is in the correct byte-order. > > This bug is apparent with ADS but it is also the case that any other > firmware routine that depends on the "bssSelfStaIdx" would retrieve > malformed data on an encrypted link. > > Fixes: 3e977c5c523d ("wcn36xx: Define wcn3680 specific firmware parameters") > Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org> > --- > drivers/net/wireless/ath/wcn36xx/main.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/wireless/ath/wcn36xx/main.c b/drivers/net/wireless/ath/wcn36xx/main.c > index 2ccf7a8924a0..60cf0516e1bc 100644 > --- a/drivers/net/wireless/ath/wcn36xx/main.c > +++ b/drivers/net/wireless/ath/wcn36xx/main.c > @@ -567,12 +567,14 @@ static int wcn36xx_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd, > if (IEEE80211_KEY_FLAG_PAIRWISE & key_conf->flags) { > sta_priv->is_data_encrypted = true; > /* Reconfigure bss with encrypt_type */ > - if (NL80211_IFTYPE_STATION == vif->type) > + if (NL80211_IFTYPE_STATION == vif->type) { > wcn36xx_smd_config_bss(wcn, > vif, > sta, > sta->addr, > true); > + wcn36xx_smd_config_sta(wcn, vif, sta); > + } > > wcn36xx_smd_set_stakey(wcn, > vif_priv->encrypt_type, > Nice write-up! Tested-by: Benjamin Li <benl@squareup.com> on Square Terminal (2018) with FW-side workaround reverted
diff --git a/drivers/net/wireless/ath/wcn36xx/main.c b/drivers/net/wireless/ath/wcn36xx/main.c index 2ccf7a8924a0..60cf0516e1bc 100644 --- a/drivers/net/wireless/ath/wcn36xx/main.c +++ b/drivers/net/wireless/ath/wcn36xx/main.c @@ -567,12 +567,14 @@ static int wcn36xx_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd, if (IEEE80211_KEY_FLAG_PAIRWISE & key_conf->flags) { sta_priv->is_data_encrypted = true; /* Reconfigure bss with encrypt_type */ - if (NL80211_IFTYPE_STATION == vif->type) + if (NL80211_IFTYPE_STATION == vif->type) { wcn36xx_smd_config_bss(wcn, vif, sta, sta->addr, true); + wcn36xx_smd_config_sta(wcn, vif, sta); + } wcn36xx_smd_set_stakey(wcn, vif_priv->encrypt_type,
We have been tracking a strange bug with Antenna Diversity Switching (ADS) on wcn3680b for a while. ADS is configured like this: A. Via a firmware configuration table baked into the firmware binary. 1. Defines if ADS is enabled. 2. Defines which GPIOs are connected to which antenna enable pin. 3. Defines which antenna/GPIO is primary and which is secondary. B. WCN36XX_CFG_VAL(ANTENNA_DIVERSITY, N) N is a bitmask of available antenna. Setting N to 3 indicates a bitmask of enabled antenna (1 | 2). Obviously then we can set N to 1 or N to 2 to fix to a particular antenna and disable antenna diversity. C. WCN36XX_CFG_VAL(ASD_PROBE_INTERVAL, XX) XX is the number of beacons between each antenna RSSI check. Setting this value to 50 means, every 50 received beacons, run the ADS algorithm. D. WCN36XX_CFG_VAL(ASD_TRIGGER_THRESHOLD, YY) YY is a two's complement integer which specifies the RSSI decibel threshold below which ADS will run. We default to -60db here, meaning a measured RSSI <= -60db will trigger an ADS probe. E. WCN36XX_CFG_VAL(ASD_RTT_RSSI_HYST_THRESHOLD, Z) Z is a hysteresis value, indicating a delta which the RSSI must exceed for the antenna switch to be valid. For example if HYST_THRESHOLD == 3 AntennaId1-RSSI == -60db and AntennaId-2-RSSI == -58db then firmware will not switch antenna. The threshold needs to be -57db or better to satisfy the criteria. ADS works like this: A. Every XX beacons the firmware switches to or remains on the primary antenna. B. The firmware then sends a Request-To-Send (RTS) packet to the AP. C. The firmware waits for a Clear-To-Send (CTS) response from the AP. D. The firmware then notes the received RSSI on the CTS packet. E. The firmware then repeats steps A-D on the secondary antenna. F. Subsequently if the measured RSSI on the primary or secondary antenna is better than ASD_TRIGGER_THRESHOLD + ASD_RTT_RSSI_HYST_THRESHOLD then that antenna becomes the active antenna. G. If RSSI rises past ASD_TRIGGER_THRESHOLD then ADS doesn't run at all even if there is a substantially better RSSI on the other antenna. What we have been observing is that the RTS packet is being sent but the MAC address is a byte-swapped version of the target MAC. The ADS/RTS MAC is corrupted only when the link is encrypted, if the AP is open the RTS MAC is correct. Similarly if we configure the firmware to an RTS/CTS sequence for regular data - the transmitted RTS MAC is correctly formatted. Internally the wcn36xx firmware uses the indexes in the SMD commands to populate and extract data from specific entries in an STA lookup table. The AP's MAC appears a number of times in different indexes within this lookup table, so the MAC address extracted for the data-transmit RTS and the MAC address extracted for the ADS/RTS packet are not the same STA table index. Our analysis indicates the relevant firmware STA table index is "bssSelfStaIdx". There is an STA populate function responsible for formatting the MAC address of the bssSelfStaIdx including byte-swapping the MAC address. Its clear then that the required STA populate command did not run for bssSelfStaIdx. So taking a look at the sequence of SMD commands sent to the firmware we see the following downstream when moving from an unencrypted to encrypted BSS setup. - WLAN_HAL_CONFIG_BSS_REQ - WLAN_HAL_CONFIG_STA_REQ - WLAN_HAL_SET_STAKEY_REQ Upstream in wcn36xx we have - WLAN_HAL_CONFIG_BSS_REQ - WLAN_HAL_SET_STAKEY_REQ The solution then is to add the missing WLAN_HAL_CONFIG_STA_REQ between WLAN_HAL_CONFIG_BSS_REQ and WLAN_HAL_SET_STAKEY_REQ. No surprise WLAN_HAL_CONFIG_STA_REQ is the routine responsible for populating the STA lookup table in the firmware and once done the MAC sent by the ADS routine is in the correct byte-order. This bug is apparent with ADS but it is also the case that any other firmware routine that depends on the "bssSelfStaIdx" would retrieve malformed data on an encrypted link. Fixes: 3e977c5c523d ("wcn36xx: Define wcn3680 specific firmware parameters") Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org> --- drivers/net/wireless/ath/wcn36xx/main.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)