net: eth-mux: try decoupling work-queue suggested by chatgpt

but still rcu lock

$ ip link set eth1 up
[   31.594416] Aeonsemi AS21xxx mdio-bus:1c: Firmware Version: 1.8.5
[   31.600622] mtk_soc_eth 15100000.ethernet eth1: PHY [mdio-bus:1c] driver [Aeonsemi AS21xxx] (irq=POLL)
[   31.617827] mtk_soc_eth 15100000.ethernet eth1: configuring for phy/usxgmii link mode
[   31.638421] mtk_soc_eth 15100000.ethernet eth1: DBG phylink_start:2654

[   91.635970] rcu: INFO: rcu_sched self-detected stall on CPU
[   91.641548] rcu:     1-....: (5999 ticks this GP) idle=feb4/1/0x4000000000000000 softirq=1332/1332 fqs=3000
[   91.651018] rcu:     (t=6000 jiffies g=489 q=16 ncpus=4)
[   91.656062] CPU: 1 UID: 0 PID: 3408 Comm: ip Not tainted 6.18.0-rc1-bpi-r4 #2 NONE
[   91.656069] Hardware name: Bananapi BPI-R4 (DT)
[   91.656071] pstate: 20400005 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   91.656076] pc : phylink_start+0xd4/0x57c
[   91.656088] lr : phylink_start+0x2cc/0x57c
[   91.656092] sp : ffffffc08826b4a0
[   91.656094] x29: ffffffc08826b4a0 x28: ffffff80c2bde080 x27: ffffffc080fbac48
[   91.656101] x26: ffffff80c0f56000 x25: ffffffc080fb9c98 x24: 0000000000000001
[   91.656106] x23: 0000000000001002 x22: ffffff80c0f56a00 x21: ffffff80c0f56000
[   91.656111] x20: 0000000000000000 x19: ffffff80c1370c00 x18: 00000000ffffffff
[   91.656116] x17: 0000000000003040 x16: 0000000000005078 x15: 0000000000000006
[   91.656121] x14: 00000000ffffffea x13: ffffffc08826b148 x12: ffffffc081869cf0
[   91.656126] x11: 0000000000000001 x10: 0000000000000001 x9 : 0000000000017fe8
[   91.656131] x8 : c0000000ffffefff x7 : ffffffc081811c70 x6 : 0000000000000001
[   91.656136] x5 : ffffff80ff761688 x4 : 0000000000000000 x3 : 0000000000000000
[   91.656140] x2 : ffffff80c1370ca0 x1 : ffffff80c0a7eca0 x0 : ffffff80c0a7ec80
[   91.656146] Call trace:
[   91.656148]  phylink_start+0xd4/0x57c (P)
[   91.656154]  mtk_open+0x45c/0xb24
[   91.656159]  __dev_open+0x110/0x228
[   91.656167]  __dev_change_flags+0x1e8/0x240
[   91.656172]  netif_change_flags+0x24/0x6c
[   91.656176]  do_setlink.isra.0+0xb50/0xe4c
[   91.656181]  rtnl_newlink+0x684/0x968

Author: frank-w

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -4919,26 +4919,17 @@ static const struct net_device_ops mtk_netdev_ops = {
 	.ndo_select_queue	= mtk_select_queue,
 };
 
-static void mux_poll(struct work_struct *work)
+static void mtk_mux_reconfig_work(struct work_struct *work)
 {
-	struct mtk_mux *mux = container_of(work, struct mtk_mux, poll.work);
+	struct mtk_mux *mux = container_of(work, struct mtk_mux, reconfig_work);
 	struct mtk_mac *mac = mux->mac;
 	struct mtk_eth *eth = mac->hw;
 	struct net_device *dev = eth->netdev[mac->id];
-	unsigned int new_channel;
-	int sfp_present;
+	unsigned int new_channel = mux->pending_channel;
 
-	//dev_info(eth->dev, "ethernet mux: %s:%d\n",__func__,__LINE__);
-	if (IS_ERR(mux->mod_def0_gpio) || IS_ERR(mux->chan_sel_gpio))
-		goto reschedule;
-
-	sfp_present = gpiod_get_value_cansleep(mux->mod_def0_gpio);
-	new_channel = sfp_present ? mux->sfp_present_channel : !mux->sfp_present_channel;
-
-	if (mux->channel == new_channel || !netif_running(dev))
-		goto reschedule;
+	if (!netif_running(dev))
+		return;
 
-	dev_info(eth->dev, "ethernet mux: line:%d new channel:%d,sfp:%d\n",__LINE__, new_channel,sfp_present);
 	rtnl_lock();
 
 	mtk_stop(dev);
@@ -4950,13 +4941,32 @@ static void mux_poll(struct work_struct *work)
 
 	gpiod_set_value_cansleep(mux->chan_sel_gpio, new_channel);
 
-	usleep_range(100000,200000);
-
 	mtk_open(dev);
 
+	mux->channel = new_channel;
+
 	rtnl_unlock();
+}
 
-	mux->channel = new_channel;
+static void mux_poll(struct work_struct *work)
+{
+	struct mtk_mux *mux = container_of(work, struct mtk_mux, poll.work);
+	struct mtk_mac *mac = mux->mac;
+	struct mtk_eth *eth = mac->hw;
+	struct net_device *dev = eth->netdev[mac->id];
+	unsigned int new_channel;
+	int sfp_present;
+
+	if (IS_ERR(mux->mod_def0_gpio) || IS_ERR(mux->chan_sel_gpio))
+		goto reschedule;
+
+	sfp_present = gpiod_get_value_cansleep(mux->mod_def0_gpio);
+	new_channel = sfp_present ? mux->sfp_present_channel : !mux->sfp_present_channel;
+
+	if (mux->channel != new_channel && netif_running(dev)) {
+		mux->pending_channel = new_channel;
+		schedule_work(&mux->reconfig_work);
+	}
 
 reschedule:
 	mod_delayed_work(system_wq, &mux->poll, msecs_to_jiffies(100));
@@ -5025,6 +5035,7 @@ static void mtk_release_mux(struct mtk_eth *eth, int id)
 		return;
 
 	cancel_delayed_work_sync(&mux->poll);
+	cancel_work_sync(&mux->reconfig_work);
 
 	if (!IS_ERR_OR_NULL(mux->mod_def0_gpio))
 		gpiod_put(mux->mod_def0_gpio);
@@ -5116,6 +5127,7 @@ static int mtk_add_mux(struct mtk_eth *eth, struct device_node *np)
 	dev_info(eth->dev, "ethernet mux: line:%d added new mux\n",__LINE__);
 	INIT_DELAYED_WORK(&mux->poll, mux_poll);
 	mod_delayed_work(system_wq, &mux->poll, msecs_to_jiffies(3000));
+	INIT_WORK(&mux->reconfig_work, mtk_mux_reconfig_work);
 
 	return 0;