Re: [net-next v4 7/8] net: wwan: prevent premature device unregister when NMEA port is present

[Sergey Ryazanov]

Hi Slark, Loic,

sorry for late joining the discussion, please find a design question below.

On 1/5/26 12:20, Slark Xiao wrote:
> From: Loic Poulain <loic.poulain@xxxxxxxxxxxxxxxx>
>
> The WWAN core unregisters the device when it has no remaining WWAN ops
> or child devices. For NMEA port types, the child is registered under
> the GNSS class instead of WWAN, so the core incorrectly assumes there
> are no children and unregisters the WWAN device too early. This leads
> to a second unregister attempt after the NMEA device is removed.
>
> To fix this issue, we register a virtual WWAN port device along the
> GNSS device, this ensures the WWAN device remains registered until
> all associated ports, including NMEA, are properly removed.

wwan core assumes whole responsibility for managing a WWAN device. We 
already use wwan_create_dev()/wwan_remove_dev() everywhere. But, we are 
checking the reminding references in an implicit way using 
device_for_each_child() and registered OPS existence. Thus, we need this 
trick with a virtual child port.

Does it make sense to switch to an explicit reference counting? We can 
introduce such counter to the wwan_device structure, and 
increment/decrement it on every wwan_create_dev()/wwan_remove_dev() 
call. So, we will do device_unregister() upon reference number becoming 
zero.

If it sounds promising, I can send a RFC, let's say, tomorrow.

--
Sergey