[PATCH net] net: stmmac: dwmac-motorcomm: fix eFUSE MAC address read failure

[Johan Alvarado]

This patch fixes an issue where reading the MAC address from the eFUSE
fails due to a race condition.

The root cause was identified by comparing the driver's behavior with a
custom U-Boot port. In U-Boot, the MAC address was read successfully
every time because the driver was loaded later in the boot process, giving
the hardware ample time to initialize. In Linux, reading the eFUSE
immediately returns all zeros, resulting in a fallback to a random MAC address.

Hardware cold-boot testing revealed that the eFUSE controller requires a
short settling time to load its internal data. Adding a 2000-5000us
delay after the reset ensures the hardware is fully ready, allowing the
native MAC address to be read consistently.

Fixes: 02ff155ea281 ("net: stmmac: Add glue driver for Motorcomm YT6801 ethernet controller")
Reported-by: Georg Gottleuber <ggo@xxxxxxxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/all/24cfefff-1233-4745-8c47-812b502d5d19@xxxxxxxxxxxxxxxxxxx/
Signed-off-by: Johan Alvarado <contact@xxxxxxxx>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac-motorcomm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-motorcomm.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-motorcomm.c
index 8b45b9cf7202..663d87ccfa0f 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-motorcomm.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-motorcomm.c
@@ -6,6 +6,7 @@
  */
 
 #include <linux/bits.h>
+#include <linux/delay.h>
 #include <linux/dev_printk.h>
 #include <linux/io.h>
 #include <linux/iopoll.h>
@@ -334,6 +335,13 @@ static int motorcomm_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 
 	motorcomm_reset(priv);
 
+	/*
+	 * After system reset, the eFuse controller needs time to load
+	 * its internal data. Without this delay, eFuse reads return
+	 * all zeros, causing MAC address detection to fail.
+	 */
+	usleep_range(2000, 5000);
+
 	ret = motorcomm_efuse_read_mac(&pdev->dev, priv, res.mac);
 	if (ret == -ENOENT) {
 		dev_warn(&pdev->dev, "eFuse contains no valid MAC address\n");
-- 
2.53.0