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

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Message-ID: <CAFEp6-1xoFW6xpQHPN4_XNtbjwvW=TUdFrOkFKwM+-rEH7WqMg@mail.gmail.com>
Date: Mon, 30 Jun 2025 09:30:14 +0200
From: Loic Poulain <loic.poulain@....qualcomm.com>
To: Sergey Ryazanov <ryazanov.s.a@...il.com>
Cc: 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, Slark Xiao <slark_xiao@....com>,
        Muhammad Nuzaihan <zaihan@...ealasia.net>,
        Qiang Yu <quic_qianyu@...cinc.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Johan Hovold <johan@...nel.org>
Subject: Re: [RFC PATCH v2 0/6] net: wwan: add NMEA port type support

Hi Sergey,


On Sun, Jun 29, 2025 at 12:07 PM Sergey Ryazanov <ryazanov.s.a@...il.com> wrote:
>
> Hi Loic,
>
> On 6/29/25 05:50, Loic Poulain wrote:
> > Hi Sergey,
> >
> > On Tue, Jun 24, 2025 at 11:39 PM Sergey Ryazanov <ryazanov.s.a@...il.com> wrote:
> >> The series introduces a long discussed NMEA port type support for the
> >> WWAN subsystem. There are two goals. From the WWAN driver perspective,
> >> NMEA exported as any other port type (e.g. AT, MBIM, QMI, etc.). From
> >> user space software perspective, the exported chardev belongs to the
> >> GNSS class what makes it easy to distinguish desired port and the WWAN
> >> device common to both NMEA and control (AT, MBIM, etc.) ports makes it
> >> easy to locate a control port for the GNSS receiver activation.
> >>
> >> Done by exporting the NMEA port via the GNSS subsystem with the WWAN
> >> core acting as proxy between the WWAN modem driver and the GNSS
> >> subsystem.
> >>
> >> The series starts from a cleanup patch. Then two patches prepares the
> >> WWAN core for the proxy style operation. Followed by a patch introding a
> >> new WWNA port type, integration with the GNSS subsystem and demux. The
> >> series ends with a couple of patches that introduce emulated EMEA port
> >> to the WWAN HW simulator.
> >>
> >> The series is the product of the discussion with Loic about the pros and
> >> cons of possible models and implementation. Also Muhammad and Slark did
> >> a great job defining the problem, sharing the code and pushing me to
> >> finish the implementation. Many thanks.
> >>
> >> Comments are welcomed.
> >>
> >> Slark, Muhammad, if this series suits you, feel free to bundle it with
> >> the driver changes and (re-)send for final inclusion as a single series.
> >>
> >> Changes RFCv1->RFCv2:
> >> * Uniformly use put_device() to release port memory. This made code less
> >>    weird and way more clear. Thank you, Loic, for noticing and the fix
> >>    discussion!
> >
> > I think you can now send that series without the RFC tag. It looks good to me.
>
> Thank you for reviewing it. Do you think it makes sense to introduce new
> API without an actual user? Ok, we have two drivers potentially ready to
> use GNSS port type, but they are not yet here. That is why I have send
> as RFC. On another hand, testing with simulator has not revealed any
> issue and GNSS port type implementation looks ready to be merged.

Right, we need a proper user for it, I think some MHI PCIe modems already
have this NMEA port available, so it can easily be added to this PR. For sure
we will need someone to test this.

> Let's wait a month or so and if no actual driver patch going to be send,
> then I will resend as formal patch to have the functionality in the
> kernel in advance.

ack.

Regards,
Loic