netdev - Re: [PATCH net v5 2/3] net: usb: ax88179_178a: add USB device driver for config selection

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Message-ID: <fe42645d-0447-4bf4-98c5-ea288f8f6f5a@rowland.harvard.edu>
Date: Tue, 21 Oct 2025 12:33:21 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Oliver Neukum <oneukum@...e.com>
Cc: Michal Pecio <michal.pecio@...il.com>, yicongsrfy@....com,
	andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, linux-usb@...r.kernel.org, netdev@...r.kernel.org,
	pabeni@...hat.com
Subject: Re: [PATCH net v5 2/3] net: usb: ax88179_178a: add USB device driver
 for config selection

On Tue, Oct 21, 2025 at 11:13:29AM +0200, Oliver Neukum wrote:
> On 20.10.25 18:59, Alan Stern wrote:
> 
> > Another possibility is simply to give up on handling all of this
> > automatically in the kernel.  The usb_modeswitch program certainly
> > should be capable of determining when a USB network device ought to
> > switch to a different configuration; that's very similar to the things
> > it does already.  Maybe userspace is the best place to implement this
> > stuff.
> 
> That would make usb_modeswitch or yet a new udev component mandatory.
> That is the exact opposite of what we would like to achieve.

In the same way that usb_modeswitch or a udev script is already 
mandatory for a bunch of other devices?

In this case, it wouldn't be quite as mandatory since the user can 
always change the configuration by hand.  Some of the things 
usb_modeswitch does probably aren't so easy to accomplish.

I agree, it would be great if the kernel could handle all these things 
for people.  But sometimes it's just a lot easier to do stuff in 
userspace.

> > Furthermore, with usb_modeswitch it's not at all uncommon to have some
> > drivers bind momentarily before being kicked off.  People don't care
> > about it very much, as long it all happens reliably and automatically.
> 
> That is probably not wise in the long run. If the device whose driver
> we kick off is a CD-ROM, nobody cares. If it is a network interface,
> we'll have to deal with ugly cases like user space already having
> sent a DHCP query when we kick the old driver off the interface.

Doesn't the same concern apply every time a network interface goes down?

Alan Stern