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

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Message-ID: <CAFEp6-3pvrMmyRg37Vyv_NhXeOukY9A4TYBE9f42zMR5i04k_Q@mail.gmail.com>
Date: Wed, 19 Nov 2025 12:27:49 +0100
From: Loic Poulain <loic.poulain@....qualcomm.com>
To: Slark Xiao <slark_xiao@....com>
Cc: Sergey Ryazanov <ryazanov.s.a@...il.com>,
        Daniele Palmas <dnlplm@...il.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

Hi Slark,

On Fri, Nov 14, 2025 at 8:08 AM Slark Xiao <slark_xiao@....com> wrote:
>
>
> 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.

We shouldn’t merge a series that is known to be broken or causes
crashes. However, based on Daniele’s feedback, the series can be
fixed.

You can check the tentative fix here:
https://github.com/loicpoulain/linux/commits/wwan/pending
This branch includes Sergey’s patch from the mailing list along with a
proposed fix.

If you can test it on your side, that would be very helpful.

Also, it’s fine to resubmit the corrected series without the RFC tag,
as long as you keep Sergey as the original author.

Regards,
Loic