tcpdump vlan problems with lan78xx driver?

[Richard Gopstein]

I was debugging code which ran on one RPi 3B+, but failed on a different 3B+. Looks like the Pi with the problem has the LAN7800 ethernet chip, but the working one has the SMSC9512/9514 Fast Ethernet Adapter.

The scenario is that we run "tcpdump -i eth0 -e vlan" on a network which has vlans. On the working RPi (and also on an x86 based Ubuntu system), tcpdump displays packets with a vlan tag. On the Pi with the LAN7800, no packets are ever displayed. We also tried booting the failing Pi off the working Pi's sdcard. The failing RPi still would not display packets, hence it appearing to be a HW/driver issue.

pi@raspberrypi:~ $ uname -a
Linux raspberrypi 4.19.58-v7+ #1245 SMP Fri Jul 12 17:25:51 BST 2019 armv7l GNU/Linux

pi@raspberrypi:~ $ dmesg | grep 78xx
[ 0.324777] usbcore: registered new interface driver lan78xx
[ 4.280187] lan78xx 1-1.1.1:1.0 (unnamed net_device) (uninitialized): No External EEPROM. Setting MAC Speed
[ 4.299811] libphy: lan78xx-mdiobus: probed
[ 4.338242] lan78xx 1-1.1.1:1.0 (unnamed net_device) (uninitialized): int urb period 64

pi@raspberrypi:~ $ tcpdump -e vlan
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes

pi@raspberrypi:~ $ tcpdump --version
tcpdump version 4.9.2
libpcap version 1.8.1
OpenSSL 1.1.1c 28 May 2019

pi@raspberrypi:~ $ lsmod
Module Size Used by
nfnetlink_queue 24576 0
nfnetlink_log 20480 0
nfnetlink 16384 2 nfnetlink_log,nfnetlink_queue
rfcomm 49152 4
bnep 20480 2
hci_uart 40960 1
btbcm 16384 1 hci_uart
serdev 20480 1 hci_uart
bluetooth 389120 29 hci_uart,bnep,btbcm,rfcomm
ecdh_generic 28672 1 bluetooth
fuse 110592 3
8021q 32768 0
garp 16384 1 8021q
stp 16384 1 garp
llc 16384 2 garp,stp
evdev 24576 2
joydev 20480 0
fb_ili9486 16384 2
fbtft 45056 1 fb_ili9486
syscopyarea 16384 1 fbtft
sysfillrect 16384 1 fbtft
sysimgblt 16384 1 fbtft
ads7846 24576 0
fb_sys_fops 16384 1 fbtft
brcmfmac 311296 0
brcmutil 16384 1 brcmfmac
raspberrypi_hwmon 16384 0
sha256_generic 20480 0
hwmon 16384 2 raspberrypi_hwmon,ads7846
cfg80211 614400 1 brcmfmac
snd_bcm2835 24576 2
snd_pcm 102400 1 snd_bcm2835
rfkill 28672 6 bluetooth,cfg80211
snd_timer 32768 1 snd_pcm
bcm2835_codec 36864 0
bcm2835_v4l2 45056 0
snd 73728 7 snd_timer,snd_bcm2835,snd_pcm
v4l2_mem2mem 24576 1 bcm2835_codec
bcm2835_mmal_vchiq 32768 2 bcm2835_codec,bcm2835_v4l2
videobuf2_dma_contig 20480 1 bcm2835_codec
v4l2_common 16384 1 bcm2835_v4l2
videobuf2_vmalloc 16384 1 bcm2835_v4l2
videobuf2_memops 16384 2 videobuf2_dma_contig,videobuf2_vmalloc
videobuf2_v4l2 24576 3 bcm2835_codec,bcm2835_v4l2,v4l2_mem2mem
videobuf2_common 45056 4 bcm2835_codec,bcm2835_v4l2,v4l2_mem2mem,videobuf2_v4l2
i2c_bcm2835 16384 0
videodev 200704 6 bcm2835_codec,v4l2_common,videobuf2_common,bcm2835_v4l2,v4l2_mem2mem,videobuf2_v4l2
media 36864 2 videodev,v4l2_mem2mem
vc_sm_cma 36864 1 bcm2835_mmal_vchiq
spi_bcm2835 20480 0
uio_pdrv_genirq 16384 0
uio 20480 1 uio_pdrv_genirq
fixed 16384 0
i2c_dev 20480 0
ip_tables 24576 0
x_tables 32768 1 ip_tables
ipv6 450560 24

[peter green (plugwash)]

This looks like a kernel issue, can you report it to the raspberry pi kernel guys?

https://github.com/raspberrypi/linux/issues

[Richard Gopstein (u-rich)]

Ok. I added it there. Do I need to do anything to it here?