netdev - RTL8156(A|B) chip requires r8156 to be force loaded to operate

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Message-ID: <20211224203018.z2n7sylht47ownga@Thors>
Date:   Fri, 24 Dec 2021 21:30:18 +0100
From:   Ryan Lahfa <ryan@...fa.xyz>
To:     netdev@...r.kernel.org
Subject: RTL8156(A|B) chip requires r8156 to be force loaded to operate

Hi all,

I recently bought an USB-C 2.5Gbps external network card, which shows in
`lsusb` as:

> Bus 002 Device 003: ID 0bda:8156 Realtek Semiconductor Corp. USB 10/100/1G/2.5G LAN

By default, on my distribution (NixOS "21.11pre319254.b5182c214fa")'s
latest kernel (`pkgs.linuxPackages_latest`) which shows in `uname -nar`
as:

> Linux $machine 5.15.10 #1-NixOS SMP Fri Dec 17 09:30:17 UTC 2021 x86_64 GNU/Linux

The network card is loaded with `cdc_ncm` driver and is unable to detect
any carrier even when one is actually plugged in, I tried multiple
things, I confirmed independently that the carrier is working.

Through further investigations and with the help of a user on
Libera.Chat #networking channel, we blacklisted `cdc_ncm`, but nothing
get loaded in turn.

Then, I forced the usage of r8152 for the device 0bda:8156 using `echo
0bda 8156 > /sys/bus/usb/drivers/r8152/new_id`, and... miracle.
Everything just worked.

I am uncertain whether this falls in kernel's responsibility or not, it
seems indeed that my device is listed for r8152: https://github.com/torvalds/linux/blob/master/drivers/net/usb/r8152.c#L9790 introduced by this commit https://github.com/torvalds/linux/commit/195aae321c829dd1945900d75561e6aa79cce208 if I understand well, which is tagged for 5.15.

I am curious to see how difficult would that be to write a patch for
this and fix it, meanwhile, here is my modest contribution with this bug
report, hopefully, this is the right place for them.

Kind regards,
-- 
Ryan Lahfa