mt7925_mcu_set_mlo_roc() uses WARN_ON_ONCE() to check if link_conf or
channel is NULL. However, during MLO AP setup, it's normal for the
channel to not be configured yet when this function is called. The
WARN_ON_ONCE triggers a kernel warning/oops that makes the system
appear to have crashed, even though it's just a timing issue.

Example kernel oops during AP setup:
  WARNING: CPU: 0 PID: 12345 at drivers/net/wireless/mediatek/mt76/mt7925/mcu.c:1345
  Call Trace:
   mt7925_mcu_set_mlo_roc+0x...
   mt7925_remain_on_channel+0x...

Replace WARN_ON_ONCE with regular NULL checks and return -ENOLINK to
indicate the link is not fully configured yet. This allows the upper
layers to retry when the link is ready, without spamming the kernel
log with warnings.

Also add a check for mconf in the first loop to match the pattern
used in the second loop, preventing potential NULL dereference.

This fixes kernel oops reported during MLO AP setup on OpenWrt with
MT7925E hardware and similar issues on standard Linux distributions.

Fixes: c5d11e4a9fa8 ("wifi: mt76: mt7925: add mt7925_change_vif_links")
Link: https://github.com/openwrt/mt76/issues/1014
Signed-off-by: Zac Bowling <zac@zacbowling.com>
---
 .../net/wireless/mediatek/mt76/mt7925/mcu.c   | 20 +++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/mcu.c b/drivers/net/wireless/mediatek/mt76/mt7925/mcu.c
index 958ff9da9f01..8080fea30d23 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/mcu.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/mcu.c
@@ -1337,15 +1337,23 @@ int mt7925_mcu_set_mlo_roc(struct mt792x_bss_conf *mconf, u16 sel_links,
 	for (i = 0; i < ARRAY_SIZE(links); i++) {
 		links[i].id = i ? __ffs(~BIT(mconf->link_id) & sel_links) :
 				 mconf->link_id;
+
 		link_conf = mt792x_vif_to_bss_conf(vif, links[i].id);
-		if (WARN_ON_ONCE(!link_conf))
-			return -EPERM;
+		if (!link_conf)
+			return -ENOLINK;
 
 		links[i].chan = link_conf->chanreq.oper.chan;
-		if (WARN_ON_ONCE(!links[i].chan))
-			return -EPERM;
+		if (!links[i].chan)
+			/* Channel not configured yet - this can happen during
+			 * MLO AP setup when links are being added sequentially.
+			 * Return -ENOLINK to indicate link not ready.
+			 */
+			return -ENOLINK;
 
 		links[i].mconf = mt792x_vif_to_link(mvif, links[i].id);
+		if (!links[i].mconf)
+			return -ENOLINK;
+
 		links[i].tag = links[i].id == mconf->link_id ?
 			       UNI_ROC_ACQUIRE : UNI_ROC_SUB_LINK;
 
@@ -1359,8 +1367,8 @@ int mt7925_mcu_set_mlo_roc(struct mt792x_bss_conf *mconf, u16 sel_links,
 		type = MT7925_ROC_REQ_JOIN;
 
 	for (i = 0; i < ARRAY_SIZE(links) && i < hweight16(vif->active_links); i++) {
-		if (WARN_ON_ONCE(!links[i].mconf || !links[i].chan))
-			continue;
+		if (!links[i].mconf || !links[i].chan)
+			return -ENOLINK;
 
 		chan = links[i].chan;
 		center_ch = ieee80211_frequency_to_channel(chan->center_freq);
-- 
2.51.0