net: ks8851-ml: Fix IRQ handling and locking

BugLink: https://bugs.launchpad.net/bugs/1868629

[ Upstream commit 44343418 ]

The KS8851 requires that packet RX and TX are mutually exclusive.
Currently, the driver hopes to achieve this by disabling interrupt
from the card by writing the card registers and by disabling the
interrupt on the interrupt controller. This however is racy on SMP.

Replace this approach by expanding the spinlock used around the
ks_start_xmit() TX path to ks_irq() RX path to assure true mutual
exclusion and remove the interrupt enabling/disabling, which is
now not needed anymore. Furthermore, disable interrupts also in
ks_net_stop(), which was missing before.

Note that a massive improvement here would be to re-use the KS8851
driver approach, which is to move the TX path into a worker thread,
interrupt handling to threaded interrupt, and synchronize everything
with mutexes, but that would be a much bigger rework, for a separate
patch.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Petr Stetiar <ynezz@true.cz>
Cc: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

drivers/net/ethernet/micrel/ks8851_mll.c

@@ -831,14 +831,17 @@ static irqreturn_t ks_irq(int irq, void *pw)
 {
 	struct net_device *netdev = pw;
 	struct ks_net *ks = netdev_priv(netdev);
+	unsigned long flags;
 	u16 status;
 
+	spin_lock_irqsave(&ks->statelock, flags);
 	/*this should be the first in IRQ handler */
 	ks_save_cmd_reg(ks);
 
 	status = ks_rdreg16(ks, KS_ISR);
 	if (unlikely(!status)) {
 		ks_restore_cmd_reg(ks);
+		spin_unlock_irqrestore(&ks->statelock, flags);
 		return IRQ_NONE;
 	}
 
@@ -864,6 +867,7 @@ static irqreturn_t ks_irq(int irq, void *pw)
 		ks->netdev->stats.rx_over_errors++;
 	/* this should be the last in IRQ handler*/
 	ks_restore_cmd_reg(ks);
+	spin_unlock_irqrestore(&ks->statelock, flags);
 	return IRQ_HANDLED;
 }
 
@@ -933,6 +937,7 @@ static int ks_net_stop(struct net_device *netdev)
 
 	/* shutdown RX/TX QMU */
 	ks_disable_qmu(ks);
+	ks_disable_int(ks);
 
 	/* set powermode to soft power down to save power */
 	ks_set_powermode(ks, PMECR_PM_SOFTDOWN);
@@ -989,10 +994,9 @@ static netdev_tx_t ks_start_xmit(struct sk_buff *skb, struct net_device *netdev)
 {
 	netdev_tx_t retv = NETDEV_TX_OK;
 	struct ks_net *ks = netdev_priv(netdev);
+	unsigned long flags;
 
-	disable_irq(netdev->irq);
-	ks_disable_int(ks);
-	spin_lock(&ks->statelock);
+	spin_lock_irqsave(&ks->statelock, flags);
 
 	/* Extra space are required:
 	*  4 byte for alignment, 4 for status/length, 4 for CRC
@@ -1006,9 +1010,7 @@ static netdev_tx_t ks_start_xmit(struct sk_buff *skb, struct net_device *netdev)
 		dev_kfree_skb(skb);
 	} else
 		retv = NETDEV_TX_BUSY;
-	spin_unlock(&ks->statelock);
-	ks_enable_int(ks);
-	enable_irq(netdev->irq);
+	spin_unlock_irqrestore(&ks->statelock, flags);
 	return retv;
 }