linux-kernel - [PATCH v2] smsc911x: add second read of EEPROM mac when possible corruption seen

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Message-ID: <20250903132610.966787-1-colin.foster@in-advantage.com>
Date: Wed,  3 Sep 2025 08:26:10 -0500
From: Colin Foster <colin.foster@...advantage.com>
To: linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Cc: Steve Glendinning <steve.glendinning@...well.net>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH v2] smsc911x: add second read of EEPROM mac when possible corruption seen

When the EEPROM MAC is read by way of ADDRH, it can return all 0s the
first time. Subsequent reads succeed.

This is fully reproduceable on the Phytec PCM049 SOM.

Re-read the ADDRH when this behaviour is observed, in an attempt to
correctly apply the EEPROM MAC address.

Signed-off-by: Colin Foster <colin.foster@...advantage.com>
---
 drivers/net/ethernet/smsc/smsc911x.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/smsc/smsc911x.c b/drivers/net/ethernet/smsc/smsc911x.c
index a2e511912e6a9..a0a4bb051a4c5 100644
--- a/drivers/net/ethernet/smsc/smsc911x.c
+++ b/drivers/net/ethernet/smsc/smsc911x.c
@@ -2162,10 +2162,20 @@ static const struct net_device_ops smsc911x_netdev_ops = {
 static void smsc911x_read_mac_address(struct net_device *dev)
 {
 	struct smsc911x_data *pdata = netdev_priv(dev);
-	u32 mac_high16 = smsc911x_mac_read(pdata, ADDRH);
-	u32 mac_low32 = smsc911x_mac_read(pdata, ADDRL);
+	u32 mac_high16, mac_low32;
 	u8 addr[ETH_ALEN];
 
+	mac_high16 = smsc911x_mac_read(pdata, ADDRH);
+	mac_low32 = smsc911x_mac_read(pdata, ADDRL);
+
+	/* The first mac_read in some setups can incorrectly read 0. Re-read it
+	 * to get the full MAC if this is observed.
+	 */
+	if (mac_high16 == 0) {
+		SMSC_TRACE(pdata, probe, "Re-read MAC ADDRH\n");
+		mac_high16 = smsc911x_mac_read(pdata, ADDRH);
+	}
+
 	addr[0] = (u8)(mac_low32);
 	addr[1] = (u8)(mac_low32 >> 8);
 	addr[2] = (u8)(mac_low32 >> 16);
-- 
2.43.0