lan743x: fix "BUG: invalid wait context" when setting rx mode

In the net core, the struct net_device_ops -> ndo_set_rx_mode()
callback is called with the dev->addr_list_lock spinlock held.

However, this driver's ndo_set_rx_mode callback eventually calls
lan743x_dp_write(), which acquires a mutex. Mutex acquisition
may sleep, and this is not allowed when holding a spinlock.

Fix by removing the dp_lock mutex entirely. Its purpose is to
prevent concurrent accesses to the data port. No concurrent
accesses are possible, because the dev->addr_list_lock
spinlock in the core only lets through one thread at a time.

Fixes: 23f0703 ("lan743x: Add main source files for new lan743x driver")
Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
Link: https://lore.kernel.org/r/20201109203828.5115-1-TheSven73@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Sven Van Asbroeck

drivers/net/ethernet/microchip/lan743x_main.c

@@ -674,14 +674,12 @@ static int lan743x_intr_open(struct lan743x_adapter *adapter)
 static int lan743x_dp_write(struct lan743x_adapter *adapter,
 			    u32 select, u32 addr, u32 length, u32 *buf)
 {
-	int ret = -EIO;
 	u32 dp_sel;
 	int i;
 
-	mutex_lock(&adapter->dp_lock);
 	if (lan743x_csr_wait_for_bit(adapter, DP_SEL, DP_SEL_DPRDY_,
 				     1, 40, 100, 100))
-		goto unlock;
+		return -EIO;
 	dp_sel = lan743x_csr_read(adapter, DP_SEL);
 	dp_sel &= ~DP_SEL_MASK_;
 	dp_sel |= select;
@@ -693,13 +691,10 @@ static int lan743x_dp_write(struct lan743x_adapter *adapter,
 		lan743x_csr_write(adapter, DP_CMD, DP_CMD_WRITE_);
 		if (lan743x_csr_wait_for_bit(adapter, DP_SEL, DP_SEL_DPRDY_,
 					     1, 40, 100, 100))
-			goto unlock;
+			return -EIO;
 	}
-	ret = 0;
 
-unlock:
-	mutex_unlock(&adapter->dp_lock);
-	return ret;
+	return 0;
 }
 
 static u32 lan743x_mac_mii_access(u16 id, u16 index, int read)
@@ -2735,7 +2730,6 @@ static int lan743x_hardware_init(struct lan743x_adapter *adapter,
 
 	adapter->intr.irq = adapter->pdev->irq;
 	lan743x_csr_write(adapter, INT_EN_CLR, 0xFFFFFFFF);
-	mutex_init(&adapter->dp_lock);
 
 	ret = lan743x_gpio_init(adapter);
 	if (ret)

drivers/net/ethernet/microchip/lan743x_main.h

@@ -712,9 +712,6 @@ struct lan743x_adapter {
 	struct lan743x_csr      csr;
 	struct lan743x_intr     intr;
 
-	/* lock, used to prevent concurrent access to data port */
-	struct mutex		dp_lock;
-
 	struct lan743x_gpio	gpio;
 	struct lan743x_ptp	ptp;