netdev - Re:Re: [RFC PATCH v2 0/6] net: wwan: add NMEA port type support

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Message-ID: <6d92e13b.5e8c.19a81315289.Coremail.slark_xiao@163.com>
Date: Fri, 14 Nov 2025 15:08:04 +0800 (CST)
From: "Slark Xiao" <slark_xiao@....com>
To: "Sergey Ryazanov" <ryazanov.s.a@...il.com>
Cc: "Daniele Palmas" <dnlplm@...il.com>,
	"Loic Poulain" <loic.poulain@....qualcomm.com>,
	"Muhammad Nuzaihan" <zaihan@...ealasia.net>,
	"Johannes Berg" <johannes@...solutions.net>,
	"Andrew Lunn" <andrew+netdev@...n.ch>,
	"Eric Dumazet" <edumazet@...gle.com>,
	"David S . Miller" <davem@...emloft.net>,
	"Jakub Kicinski" <kuba@...nel.org>,
	"Paolo Abeni" <pabeni@...hat.com>, netdev@...r.kernel.org,
	"Qiang Yu" <quic_qianyu@...cinc.com>,
	"Manivannan Sadhasivam" <mani@...nel.org>,
	"Johan Hovold" <johan@...nel.org>
Subject: Re:Re: [RFC PATCH v2 0/6] net: wwan: add NMEA port type support


At 2025-10-13 06:55:28, "Sergey Ryazanov" <ryazanov.s.a@...il.com> wrote:
>Hi Daniele,
>
>On 10/10/25 16:47, Daniele Palmas wrote:
>> Il giorno mer 8 ott 2025 alle ore 23:00 Sergey Ryazanov
>> <ryazanov.s.a@...il.com> ha scritto:
>>> On 10/2/25 18:44, Loic Poulain wrote:
>>>> On Tue, Sep 30, 2025 at 9:22 AM Daniele Palmas <dnlplm@...il.com> wrote:
>>>> [...]
>>>>> diff --git a/drivers/net/wwan/wwan_hwsim.c b/drivers/net/wwan/wwan_hwsim.c
>>>>> index a748b3ea1602..e4b1bbff9af2 100644
>>>>> --- a/drivers/net/wwan/wwan_hwsim.c
>>>>> +++ b/drivers/net/wwan/wwan_hwsim.c
>>>>> @@ -236,7 +236,7 @@ static void wwan_hwsim_nmea_emul_timer(struct timer_list *t)
>>>>>           /* 43.74754722298909 N 11.25759835922875 E in DMM format */
>>>>>           static const unsigned int coord[4 * 2] = { 43, 44, 8528, 0,
>>>>>                                                      11, 15, 4559, 0 };
>>>>> -       struct wwan_hwsim_port *port = from_timer(port, t, nmea_emul.timer);
>>>>> +       struct wwan_hwsim_port *port = timer_container_of(port, t,
>>>>> nmea_emul.timer);
>>>>>
>>>>> it's basically working fine in operative mode though there's an issue
>>>>> at the host shutdown, not able to properly terminate.
>>>>>
>>>>> Unfortunately I was not able to gather useful text logs besides the picture at
>>>>>
>>>>> https://drive.google.com/file/d/13ObWikuiMMUENl2aZerzxFBg57OB1KNj/view?usp=sharing
>>>>>
>>>>> showing an oops with the following call stack:
>>>>>
>>>>> __simple_recursive_removal
>>>>> preempt_count_add
>>>>> __pfx_remove_one
>>>>> wwan_remove_port
>>>>> mhi_wwan_ctrl_remove
>>>>> mhi_driver_remove
>>>>> device_remove
>>>>> device_del
>>>>>
>>>>> but the issue is systematic. Any idea?
>>>>>
>>>>> At the moment I don't have the time to debug this deeper, I don't even
>>>>> exclude the chance that it could be somehow related to the modem. I
>>>>> would like to further look at this, but I'm not sure exactly when I
>>>>> can....
>>>>
>>>> Thanks a lot for testing, Sergey, do you know what is wrong with port removal?
>>>
>>> Daniele, thanks a lot for verifying the proposal on a real hardware and
>>> sharing the build fix.
>>>
>>> Unfortunately, I unable to reproduce the crash. I have tried multiple
>>> times to reboot a VM running the simulator module even with opened GNSS
>>> device. No luck. It reboots and shutdowns smoothly.
>>>
>> 
>> I've probably figured out what's happening.
>> 
>> The problem seems that the gnss device is not considered a wwan_child
>> by is_wwan_child and this makes device_unregister in wwan_remove_dev
>> to be called twice.
>> 
>> For testing I've overwritten the gnss device class with the following hack:
>> 
>> diff --git a/drivers/net/wwan/wwan_core.c b/drivers/net/wwan/wwan_core.c
>> index 4d29fb8c16b8..32b3f7c4a402 100644
>> --- a/drivers/net/wwan/wwan_core.c
>> +++ b/drivers/net/wwan/wwan_core.c
>> @@ -599,6 +599,7 @@ static int wwan_port_register_gnss(struct wwan_port *port)
>>                  gnss_put_device(gdev);
>>                  return err;
>>          }
>> +       gdev->dev.class = &wwan_class;
>> 
>>          dev_info(&wwandev->dev, "port %s attached\n", dev_name(&gdev->dev));
>> 
>> and now the system powers off without issues.
>> 
>> So, not sure how to fix it properly, but at least does the analysis
>> make sense to you?
>
>Nice catch! I had a doubt regarding correct child port detection. Let me 
>double check, and thank you for pointing me to the possible source of 
>issues.
>
>--
>Sergey

Hi Sergey,
Sorry for bothering this thread again.
Do we have any updates on this potential issue? If this issue is not a big problem,
Could we commit these patches into a branch then every one could help debug
it based on this base code? 
I think we shall have a base to develop. No code is perfect.

Thanks.