netdev - [PATCH net] lan78xx: Resolve issue with changing MAC address

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Message-ID: <SN6PR12MB2765BEF510D47A4F34F61E6CC9BD0@SN6PR12MB2765.namprd12.prod.outlook.com>
Date:   Tue, 18 Dec 2018 05:38:22 +0000
From:   Jason Martinsen <jasonmartinsen@....com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net] lan78xx: Resolve issue with changing MAC address

Current state for the lan78xx driver does not allow for changing the MAC address of the interface, without either removing the module (if you compiled it that way) or rebooting the machine.  If you attempt to change the MAC address, ifconfig will show the new address, however, the system/interface will not respond to any traffic using that configuration.  A few short-term options to work around this are to unload the module and reload it with the new MAC address, change the interface to "promisc", or reboot with the correct configuration to change the MAC.

This patch enables the ability to change the MAC address via fairly normal means...
ifdown <interface>
modify entry in /etc/network/interfaces OR a similar method   
ifup <interface>
Then test via any network communication, such as ICMP requests to gateway.

My only test platform for this patch has been a raspberry pi model 3b+.

Signed-off-by: Jason Martinsen <jasonmartinsen@....com>

-----

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index be1917be28f2..77d3c85febf1 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -2320,6 +2320,10 @@ static int lan78xx_set_mac_addr(struct net_device *netdev, void *p)
        ret = lan78xx_write_reg(dev, RX_ADDRL, addr_lo);
        ret = lan78xx_write_reg(dev, RX_ADDRH, addr_hi);

+       /* Added to support MAC address changes */
+       ret = lan78xx_write_reg(dev, MAF_LO(0), addr_lo);
+       ret = lan78xx_write_reg(dev, MAF_HI(0), addr_hi | MAF_HI_VALID_);
+
        return 0;
 }