LEDE on Archer C7 - jumbo frame not working

For Developers
1

Hi guys,

First of all - thanks for all the hard work in making the LEDE project a continuation of our beloved wrt platform.
My device is a Trendnet TEW-823DRU router which has quite a similar hardware as TP-Link Archer C7 v2 beside the 256 RAM. I am using the latest release candidate of LEDE. The problem i have is related with AR8327N switich and jumbo frames not working properly as you can see below:

root@OpenWrt:~# ifconfig eth1 down
root@OpenWrt:~# ifconfig eth1 mtu 9000
ifconfig: SIOCSIFMTU: Invalid argument
root@OpenWrt:~# ifconfig eth1 mtu 4072
ifconfig: SIOCSIFMTU: Invalid argument
root@OpenWrt:~# ifconfig eth1 mtu 4070
root@OpenWrt:~# ifconfig eth1 up

Would appreciate if you can fix it within the next releases.

2

This seems to be a known issue for a couple of years already https://dev.openwrt.org/ticket/18296

Would love to see this fixed.

3

FWIW something's definitely wrong with the driver. I turned off GRO with ethtool and saw a latency reduction on my WAN connection of ~5ms. Maybe it'll be smaller if I actually test it multiple times but I definitely feel it.

4

Not work on AG300H. I think all ar71xx not work too.

5

I made a pull request on GitHub, containing possible fix for the issue. For now, you can test these builds for TP-Link Archer C7 v2.