net: stmmac: dwmac4: extend timeout for VLAN Tag register busy bit check

Increase the timeout for checking the busy bit of the VLAN Tag register
from 10µs to 500ms. This change is necessary to accommodate scenarios
where Energy Efficient Ethernet (EEE) is enabled.

Overnight testing revealed that when EEE is active, the busy bit can
remain set for up to approximately 300ms. The new 500ms timeout provides
a safety margin.

Fixes: ed64639 ("net: stmmac: Add support for VLAN Rx filtering")
Reviewed-by: Andrew Lunn <[email protected]>
Signed-off-by: Shenwei Wang <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: Shenwei Wang

drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c

@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/ethtool.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include "stmmac.h"
 #include "stmmac_pcs.h"
 #include "dwmac4.h"
@@ -471,7 +472,7 @@ static int dwmac4_write_vlan_filter(struct net_device *dev,
 				    u8 index, u32 data)
 {
 	void __iomem *ioaddr = (void __iomem *)dev->base_addr;
-	int i, timeout = 10;
+	int ret;
 	u32 val;
 
 	if (index >= hw->num_vlan)
@@ -487,16 +488,15 @@ static int dwmac4_write_vlan_filter(struct net_device *dev,
 
 	writel(val, ioaddr + GMAC_VLAN_TAG);
 
-	for (i = 0; i < timeout; i++) {
-		val = readl(ioaddr + GMAC_VLAN_TAG);
-		if (!(val & GMAC_VLAN_TAG_CTRL_OB))
-			return 0;
-		udelay(1);
+	ret = readl_poll_timeout(ioaddr + GMAC_VLAN_TAG, val,
+				 !(val & GMAC_VLAN_TAG_CTRL_OB),
+				 1000, 500000);
+	if (ret) {
+		netdev_err(dev, "Timeout accessing MAC_VLAN_Tag_Filter\n");
+		return -EBUSY;
 	}
 
-	netdev_err(dev, "Timeout accessing MAC_VLAN_Tag_Filter\n");
-
-	return -EBUSY;
+	return 0;
 }
 
 static int dwmac4_add_hw_vlan_rx_fltr(struct net_device *dev,