net: usb: cdc_ether: add quirk for AMI BMC stale link events

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On AMD Genoa/Turin platforms the BMC-provided USB-Ethernet gadget
(American Megatrends, VID 0x046b PID 0xffb0) intermittently fails to
respond to ARP after AC cold boot.  usbmon captures a stale
NETWORK_CONNECTION(off) immediately followed by
NETWORK_CONNECTION(on) on the interrupt endpoint (~130us apart)
after enumeration.  Because alloc_netdev() leaves
__LINK_STATE_NOCARRIER cleared, netif_carrier_ok() returns true
when the spurious OFF arrives, so usbnet_cdc_status() cannot
recognise it as redundant and schedules EVENT_LINK_CHANGE.
__handle_link_change() then calls unlink_urbs(), killing ~60 rx
URBs whose payload has already been DMA'd into memory — xHCI trace
confirms them completing as -ECONNRESET with non-zero residual
length.  rx_complete() drops these unconditionally.  The following
ON restores the carrier and re-submits URBs, but the ARP reply is
already lost; the interface looks "up but silent" until ifdown/ifup.

Fix this by adding a device-specific quirk with FLAG_LINK_INTR set,
which makes usbnet_probe() call netif_carrier_off() after bind.
With initial carrier == OFF, usbnet_cdc_status() recognises the
spurious OFF as matching the current state and drops it; the
subsequent ON is the first real event and brings the link up
cleanly without ever tearing down the rx queue.  The scheduled
link-change kevent is harmless because EVENT_DEV_OPEN is not yet
set at probe time.

This is applied as a device-specific quirk rather than a change to
the shared cdc_info driver_info because some CDC devices never
send NETWORK_CONNECTION notifications; forcing carrier off for
them would leave the link permanently DOWN.  Restricting the change
to this VID/PID keeps that class of device untouched.

Tested on Genoa and Turin across 100+ AC cold boot cycles; ping
first-packet success rate went from intermittent to 100%.

Signed-off-by: Jinhui Guo <guojinhui.liam@bytedance.com>
Link: https://patch.msgid.link/20260730051341.24930-1-guojinhui.liam@bytedance.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

...

This commit is contained in:

Jinhui Guo 2026-07-30 13:13:41 +08:00 • committed by Jakub Kicinski

parent 90359b5288

commit 089ca284af

1 changed files with 16 additions and 0 deletions

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drivers/net/usb/cdc_ether.c

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