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From: Adam Bennett <>
To: "Bjørn Mork" <>
Cc: Felipe Balbi <>,
	Greg Kroah-Hartman <>,
Subject: Re: Possible bug with cdc_ether, triggers NETDEV WATCHDOG
Date: Wed, 9 Oct 2019 09:27:48 -0400
Message-ID: <> (raw)
In-Reply-To: <>

On 10/9/19 4:53 AM, Bjørn Mork wrote:

> Adam Bennett <> writes:
>> I've been messing around with a Raspberry Pi Zero, in its ethernet
>> gadget mode.  This possible bug report is not against the Pi Zero
>> linux kernel, but rather the host computer's linux kernel.  I've been
>> able to reproduce the same host computer issue with my normal laptop,
>> and an embedded board (buildroot-based). Both run a newish version of
>> 4.19.
> The issue is reported on the host, but it's really a problem with the
> gadget.  You'll probably have the same issues with any host, including
> hosts running something other than Linux.  They just won't be as verbose
> about it.
That was my original assumption also.  But I tested the Pi Zero on 
Windows 10 (build 1903) and latest MacOS, and it works fine on those 
>> The bug report is that most of the time I cannot ping through the
>> local link, and I get a kernel debug message:  sometimes I can ping
>> the Pi Zero with no kernel message, most of the time I can't ping and
>> the message comes up, and occasionally I get the message right when I
>> plug in the Pi Zero, before I issue the ping command.
>> Here is the dmesg on my normal laptop (I've included the plug-in
>> sequence also):
>> [11728.029900] usb 1-1: new high-speed USB device number 10 using xhci_hcd
>> [11728.434200] usb 1-1: device descriptor read/64, error -71
> First symptom of something wrong with the gadget...
>> [11728.669543] usb 1-1: New USB device found, idVendor=0525,
>> idProduct=a4a2, bcdDevice= 4.19
>> [11728.669548] usb 1-1: New USB device strings: Mfr=1, Product=2,
>> SerialNumber=0
>> [11728.669551] usb 1-1: Product: RNDIS/Ethernet Gadget
>> [11728.669554] usb 1-1: Manufacturer: Linux 4.19.75+ with 20980000.usb
>> [11728.674528] cdc_ether 1-1:1.0 usb0: register 'cdc_ether' at
>> usb-0000:00:14.0-1, CDC Ethernet Device, 22:93:3a:1e:ac:5c
>> [11730.725278] cdc_ether 1-1:1.0 enp0s20f0u1: renamed from usb0
>> [11768.174915] ------------[ cut here ]------------
>> [11768.174921] NETDEV WATCHDOG: enp0s20f0u1 (cdc_ether): transmit
>> queue 0 timed out
> This warning means that the gadget doesn't accept the packets we send
> it.  There isn't much the host can do about that, except dropping
> packets on the floor.  Which is why the warning is this loud.
Would a firewall on either the linux host or the Pi Zero cause the same 
problem (and message)?
> Bjørn

  reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-07 21:15 Adam Bennett
2019-10-09  8:53 ` Bjørn Mork
2019-10-09 13:27   ` Adam Bennett [this message]
2019-10-14  9:04     ` Oliver Neukum

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