net: usb: lan78xx: restore VLAN and hash filters after link up

Configured VLANs intermittently stop receiving traffic after a link
down/up cycle, e.g. when the network cable is unplugged and plugged back
in. VLAN filtering stays enabled but all VLAN-tagged frames are dropped
until a VLAN is added or removed again.

The LAN7801 datasheet (DS00002123E) states:

  "A portion of the MAC operates on clocks generated by the Ethernet
   PHY. During a PHY reset event, this portion of the MAC is designed to
   not be taken out of reset until the PHY clocks are operational"
  (section 8.10, MAC Reset Watchdog Timer)

  "After a reset event, the RFE will automatically initialize the
   contents of the VHF to 0h."
  (section 7.1.4, VHF Organization)

Thus a link down/up cycle stops and restarts the PHY clock, resets the
PHY-clocked portion of the MAC, and the RFE clears its VLAN/DA hash
filter (VHF) memory. The VHF holds both the VLAN filter table and the
multicast hash table, but the driver never reprograms either from its
shadow copy once the link is back, so both stay empty.

Reprogram the VLAN filter and multicast hash tables on link up.

Reported-by: Sven Schuchmann <schuchmann@schleissheimer.de>
Closes: https://lore.kernel.org/netdev/BEZP281MB224501E38B30BFDC4BD3D364D9E32@BEZP281MB2245.DEUP281.PROD.OUTLOOK.COM/T/#u
Tested-by: Sven Schuchmann <schuchmann@schleissheimer.de>
Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
Link: https://patch.msgid.link/20260622102911.484045-1-nb@tipi-net.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions