linux-kernel - cdc_ncm doesn't detect link unless ethtool is run (ASIX AX88179B)

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Message-ID: <1c3f0582-4c92-41b3-a3db-5158661d4e1a@ya.ru>
Date: Sat, 15 Nov 2025 11:58:23 +0300
From: WGH <da-wgh@...ru>
To: oliver@...kum.org, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 linux-usb@...r.kernel.org, netdev@...r.kernel.org,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: cdc_ncm doesn't detect link unless ethtool is run (ASIX AX88179B)

Hello.

I'm running Linux 6.17.7, and recently obtained a UGREEN 6 in 1 hub containing an AX88179B chip.

By default, it uses the generic cdc_ncm driver, and it works mostly okay.

The annoying problem I have is that most of the time the kernel doesn't notice that the link is up. ip link reports NO-CARRIER, network management daemon doesn't configure the interface, and so on.

The workaround I found is to run ethtool enp6s0f4u1u2c2. As soon as I do that, NO-CARRIER disappears, and network connection configures normally.

There are no interesting dmesg messages. No link status reports, just a couple of messages just after driver initiialization.

Nov 14 12:51:47 sixty-four kernel: usb 5-1.2: new SuperSpeed USB device number 19 using xhci_hcd
Nov 14 12:51:47 sixty-four kernel: usb 5-1.2: New USB device found, idVendor=0b95, idProduct=1790, bcdDevice= 2.00
Nov 14 12:51:47 sixty-four kernel: usb 5-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
Nov 14 12:51:47 sixty-four kernel: usb 5-1.2: Product: AX88179B
Nov 14 12:51:47 sixty-four kernel: usb 5-1.2: Manufacturer: ASIX
Nov 14 12:51:47 sixty-four kernel: usb 5-1.2: SerialNumber: 0000000000BE7F
Nov 14 12:51:47 sixty-four kernel: cdc_ncm 5-1.2:2.0: MAC-Address: XX:XX:XX:XX:XX:XX
Nov 14 12:51:47 sixty-four kernel: cdc_ncm 5-1.2:2.0: setting rx_max = 16384
Nov 14 12:51:47 sixty-four kernel: cdc_ncm 5-1.2:2.0: setting tx_max = 16384
Nov 14 12:51:47 sixty-four kernel: cdc_ncm 5-1.2:2.0 eth0: register 'cdc_ncm' at usb-0000:06:00.4-1.2, CDC NCM (NO ZLP), XX:XX:XX:XX:XX:XX
Nov 14 12:51:47 sixty-four kernel: cdc_ncm 5-1.2:2.0 enp6s0f4u1u2c2: renamed from eth0