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.

> 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.


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