[PATCH net] net: usb: lan78xx: reject invalid EEPROM write requests

The runtime PM handling removed the -EINVAL return for invalid
EEPROM/OTP write requests. These requests now return zero from a
successful usb_autopm_get_interface() call, even though no data is
written.

Set ret to -EINVAL for invalid requests while preserving the runtime
PM reference release.

Fixes: 8a7ffeb795f8 ("lan78xx: Fix for eeprom read/write when device auto suspend")
Signed-off-by: Stefano Munari <redacted>
---
Tested on a Raspberry Pi 3 Model B+ with the onboard Ethernet
controller, using raspberrypi/linux commit bba53a117a4a on the
rpi-6.6.y branch as the baseline.

  ethtool -E eth0 magic 0 offset 0 length 1 value 0

The command succeeds without the patch and reports "Invalid argument"
with the patch applied.
---
 drivers/net/usb/lan78xx.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 5655941f1478..7ac263454d45 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c

@@ -1719,6 +1719,8 @@ static int lan78xx_ethtool_set_eeprom(struct net_device *netdev,
 		 (ee->len == 512) &&
 		 (data[0] == OTP_INDICATOR_1))
 		ret = lan78xx_write_raw_otp(dev, ee->offset, ee->len, data);
+	else
+		ret = -EINVAL;
 
 	usb_autopm_put_interface(dev->intf);
 

-- 
2.55.0