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

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

[WGH]

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

Re: cdc_ncm doesn't detect link unless ethtool is run (ASIX AX88179B)

[Oliver Neukum]

[-- Attachment #1: Type: text/plain, Size: 535 bytes --]

On 15.11.25 09:58, WGH wrote:
> 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.

Hi,

that strongly points to a race condition.
Could you try the attached diagnostic patch?

	Regards
		Oliver

[-- Attachment #2: ncm_bind_uncond.patch --]
[-- Type: text/x-patch, Size: 442 bytes --]

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 1d9faa70ba3b..d042ba574217 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1892,7 +1892,7 @@ usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod)
 
 	netif_device_attach(net);
 
-	if (dev->driver_info->flags & FLAG_LINK_INTR)
+	//if (dev->driver_info->flags & FLAG_LINK_INTR)
 		usbnet_link_change(dev, 0, 0);
 
 	return 0;

Re: cdc_ncm doesn't detect link unless ethtool is run (ASIX AX88179B)

[WGH]

On 11/15/25 15:33, Oliver Neukum wrote:
> On 15.11.25 09:58, WGH wrote:
>> 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.
>
> Hi,
>
> that strongly points to a race condition.
> Could you try the attached diagnostic patch?
>
>     Regards
>         Oliver

Nope, this patch doesn't help.