[BUG] brcmfmac: brcmf_sdio_bus_rxctl: resumed on timeout (WiFi dies)

Hello,

After updating to Ubuntu 21.04 I found two problems related to the BRCMF_C_GET_ASSOCLIST using an older BCM4329 SDIO WiFi.

1. The kernel is spammed with:

 ieee80211 phy0: brcmf_cfg80211_dump_station: BRCMF_C_GET_ASSOCLIST unsupported, err=-52
 ieee80211 phy0: brcmf_cfg80211_dump_station: BRCMF_C_GET_ASSOCLIST unsupported, err=-52
 ieee80211 phy0: brcmf_cfg80211_dump_station: BRCMF_C_GET_ASSOCLIST unsupported, err=-52

Which happens apparently due to a newer NetworkManager version that pokes dump_station() periodically. I sent [1] that fixes this noise.

[1] https://patchwork.kernel.org/project/linux-wireless/list/?series=480715

2. The other much worse problem is that WiFi eventually dies now with these errors:

...
 ieee80211 phy0: brcmf_cfg80211_dump_station: BRCMF_C_GET_ASSOCLIST unsupported, err=-52
 brcmfmac: brcmf_sdio_bus_rxctl: resumed on timeout
 ieee80211 phy0: brcmf_cfg80211_dump_station: BRCMF_C_GET_ASSOCLIST unsupported, err=-110
 ieee80211 phy0: brcmf_proto_bcdc_query_dcmd: brcmf_proto_bcdc_msg failed w/status -110

From this point all firmware calls start to fail with err=-110 and WiFi doesn't work anymore. This problem is reproducible with 5.13-rc and current -next, I haven't checked older kernel versions. Somehow it's worse using a recent -next, WiFi dies quicker.

What's interesting is that I see that there is always a pending signal in brcmf_sdio_dcmd_resp_wait() when timeout happens. It looks like the timeout happens when there is access to a swap partition, which stalls system for a second or two, but this is not 100%. Increasing DCMD_RESP_TIMEOUT doesn't help.

Please let me know if you have any ideas of how to fix this trouble properly or if you need need any more info.

Removing BRCMF_C_GET_ASSOCLIST firmware call entirely from the driver fixes the problem.

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c
index f4405d7861b6..6327cb38d6ec 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c

@@ -2886,22 +2886,6 @@ brcmf_cfg80211_dump_station(struct wiphy *wiphy, struct net_device *ndev,
 
 	brcmf_dbg(TRACE, "Enter, idx %d\n", idx);
 
-	if (idx == 0) {
-		cfg->assoclist.count = cpu_to_le32(BRCMF_MAX_ASSOCLIST);
-		err = brcmf_fil_cmd_data_get(ifp, BRCMF_C_GET_ASSOCLIST,
-					     &cfg->assoclist,
-					     sizeof(cfg->assoclist));
-		if (err) {
-			bphy_err(drvr, "BRCMF_C_GET_ASSOCLIST unsupported, err=%d\n",
-				 err);
-			cfg->assoclist.count = 0;
-			return -EOPNOTSUPP;
-		}
-	}
-	if (idx < le32_to_cpu(cfg->assoclist.count)) {
-		memcpy(mac, cfg->assoclist.mac[idx], ETH_ALEN);
-		return brcmf_cfg80211_get_station(wiphy, ndev, mac, sinfo);
-	}
 	return -ENOENT;
 }