Some Marvell AP firmware used with mwl8k misbehaves when beacon frames
do not contain a WLAN_EID_DS_PARAMS information element with the current
channel. It was reported on OpenWrt Github issues [0].

When hostapd/mac80211 omits DS Params from the beacon (which is valid on
some bands), the firmware stops transmitting sane frames and RX status
starts reporting bogus channel information. This makes AP mode unusable.

Newer Marvell drivers (mwlwifi [1]) hard-code DS Params IE into AP beacons
for all chips, which suggests this is a firmware requirement rather than
a mwl8k-specific quirk.

Mirror that behaviour in mwl8k: when setting the beacon, check if
WLAN_EID_DS_PARAMS is present, and if not, extend the beacon and inject
a DS Params IE at the beginning of the IE list, using the current
channel from hw->conf.chandef.chan.

Tested on Linksys EA4500 (88W8366).

[0] https://github.com/openwrt/openwrt/issues/19088
[1] https://github.com/kaloz/mwlwifi/blob/db97edf20fadea2617805006f5230665fadc6a8c/hif/fwcmd.c#L675

Tested-by: Antony Kolitsos <zeusomighty@hotmail.com>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
---
 drivers/net/wireless/marvell/mwl8k.c | 61 +++++++++++++++++++++++++---
 1 file changed, 56 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/marvell/mwl8k.c b/drivers/net/wireless/marvell/mwl8k.c
index 891e125ad30b..97462d05c9ab 100644
--- a/drivers/net/wireless/marvell/mwl8k.c
+++ b/drivers/net/wireless/marvell/mwl8k.c
@@ -2966,6 +2966,42 @@ mwl8k_cmd_rf_antenna(struct ieee80211_hw *hw, int antenna, int mask)
 /*
  * CMD_SET_BEACON.
  */
+
+static bool mwl8k_beacon_has_ds_params(const u8 *buf, int len)
+{
+	const struct ieee80211_mgmt *mgmt = (const void *)buf;
+	int ies_len;
+
+	if (len <= offsetof(struct ieee80211_mgmt, u.beacon.variable))
+		return false;
+
+	ies_len = len - offsetof(struct ieee80211_mgmt, u.beacon.variable);
+
+	return cfg80211_find_ie(WLAN_EID_DS_PARAMS, mgmt->u.beacon.variable,
+				ies_len) != NULL;
+}
+
+static void mwl8k_beacon_copy_inject_ds_params(struct ieee80211_hw *hw,
+					       u8 *buf_dst, const u8 *buf_src,
+					       int src_len)
+{
+	const struct ieee80211_mgmt *mgmt = (const void *)buf_src;
+	const u8 *ies;
+	int hdr_len, left;
+
+	ies = mgmt->u.beacon.variable;
+	hdr_len = ies - buf_src;
+	left = src_len - hdr_len;
+
+	memcpy(buf_dst, buf_src, hdr_len);
+
+	/* Inject a DS Params IE at the beginning of the IE list */
+	buf_dst[hdr_len + 0] = WLAN_EID_DS_PARAMS;
+	buf_dst[hdr_len + 1] = 1;
+	buf_dst[hdr_len + 2] = hw->conf.chandef.chan->hw_value;
+
+	memcpy(buf_dst + hdr_len + 3, buf_src + hdr_len, left);
+}
 struct mwl8k_cmd_set_beacon {
 	struct mwl8k_cmd_pkt_hdr header;
 	__le16 beacon_len;
@@ -2975,17 +3011,32 @@ struct mwl8k_cmd_set_beacon {
 static int mwl8k_cmd_set_beacon(struct ieee80211_hw *hw,
 				struct ieee80211_vif *vif, u8 *beacon, int len)
 {
+	bool ds_params_present = mwl8k_beacon_has_ds_params(beacon, len);
 	struct mwl8k_cmd_set_beacon *cmd;
-	int rc;
+	int rc, final_len = len;
 
-	cmd = kzalloc(sizeof(*cmd) + len, GFP_KERNEL);
+	if (!ds_params_present)
+		/*
+		 * mwl8k firmware requires a DS Params IE with the current
+		 * channel in AP beacons. If mac80211/hostapd does not
+		 * include it, inject one here. IE ID + length + channel
+		 * number = 3 bytes.
+		 */
+		final_len += 3;
+
+	cmd = kzalloc(sizeof(*cmd) + final_len, GFP_KERNEL);
 	if (cmd == NULL)
 		return -ENOMEM;
 
 	cmd->header.code = cpu_to_le16(MWL8K_CMD_SET_BEACON);
-	cmd->header.length = cpu_to_le16(sizeof(*cmd) + len);
-	cmd->beacon_len = cpu_to_le16(len);
-	memcpy(cmd->beacon, beacon, len);
+	cmd->header.length = cpu_to_le16(sizeof(*cmd) + final_len);
+	cmd->beacon_len = cpu_to_le16(final_len);
+
+	if (ds_params_present)
+		memcpy(cmd->beacon, beacon, len);
+	else
+		mwl8k_beacon_copy_inject_ds_params(hw, cmd->beacon, beacon,
+						   len);
 
 	rc = mwl8k_post_pervif_cmd(hw, vif, &cmd->header);
 	kfree(cmd);
-- 
2.34.1

Missing wifi: prefix.

> +
> +	/* Inject a DS Params IE at the beginning of the IE list */

It hasn't really been called "IE" ("information element") in years, just
"element". Might want to update your terminology (at least for new
code), same also in subect. Also the element you're talking about is
(now?) "DSSS Parameter Set" in the spec.

> +	buf_dst[hdr_len + 0] = WLAN_EID_DS_PARAMS;
> +	buf_dst[hdr_len + 1] = 1;
> +	buf_dst[hdr_len + 2] = hw->conf.chandef.chan->hw_value;

That's wrong, it should be after the SSID and Supported Rates and BSS
Membership Selectors elements.

Normally this doesn't matter much, but I wouldn't be surprised if there
were implementations that assume the SSID is at a fixed first position.

johannes