Message-ID: <CAFEp6-1Kk1QyT-akDXXqxgJRjvL+-On2x0zmafHETJYQ0UkVqg@mail.gmail.com>
Date: Tue, 6 Jan 2026 21:36:30 +0100
From: Loic Poulain <loic.poulain@....qualcomm.com>
To: Slark Xiao <slark_xiao@....com>
Cc: ryazanov.s.a@...il.com, johannes@...solutions.net, andrew+netdev@...n.ch,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, mani@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Muhammad Nuzaihan <zaihan@...ealasia.net>,
        Qiang Yu <quic_qianyu@...cinc.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Johan Hovold <johan@...nel.org>, kernel test robot <lkp@...el.com>
Subject: Re: [net-next v4 4/8] net: wwan: add NMEA port support

On Mon, Jan 5, 2026 at 11:21 AM Slark Xiao <slark_xiao@....com> wrote:
>
> From: Sergey Ryazanov <ryazanov.s.a@...il.com>
>
> Many WWAN modems come with embedded GNSS receiver inside and have a
> dedicated port to output geopositioning data. On the one hand, the
> GNSS receiver has little in common with WWAN modem and just shares a
> host interface and should be exported using the GNSS subsystem. On the
> other hand, GNSS receiver is not automatically activated and needs a
> generic WWAN control port (AT, MBIM, etc.) to be turned on. And a user
> space software needs extra information to find the control port.
>
> Introduce the new type of WWAN port - NMEA. When driver asks to register
> a NMEA port, the core allocates common parent WWAN device as usual, but
> exports the NMEA port via the GNSS subsystem and acts as a proxy between
> the device driver and the GNSS subsystem.
>
> From the WWAN device driver perspective, a NMEA port is registered as a
> regular WWAN port without any difference. And the driver interacts only
> with the WWAN core. From the user space perspective, the NMEA port is a
> GNSS device which parent can be used to enumerate and select the proper
> control port for the GNSS receiver management.
>
> Add the description for structure member gnss in wwan_port.
>
> CC: Slark Xiao <slark_xiao@....com>
> CC: Muhammad Nuzaihan <zaihan@...ealasia.net>
> CC: Qiang Yu <quic_qianyu@...cinc.com>
> CC: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> CC: Johan Hovold <johan@...nel.org>
>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202512312143.W82zclxI-lkp@intel.com/
> Suggested-by: Loic Poulain <loic.poulain@....qualcomm.com>
> Signed-off-by: Sergey Ryazanov <ryazanov.s.a@...il.com>

Reviewed-by: Loic Poulain <loic.poulain@....qualcomm.com>

> ---
>  drivers/net/wwan/Kconfig     |   1 +
>  drivers/net/wwan/wwan_core.c | 156 +++++++++++++++++++++++++++++++++--
>  include/linux/wwan.h         |   2 +
>  3 files changed, 154 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/wwan/Kconfig b/drivers/net/wwan/Kconfig
> index 410b0245114e..88df55d78d90 100644
> --- a/drivers/net/wwan/Kconfig
> +++ b/drivers/net/wwan/Kconfig
> @@ -7,6 +7,7 @@ menu "Wireless WAN"
>
>  config WWAN
>         tristate "WWAN Driver Core"
> +       depends on GNSS || GNSS = n
>         help
>           Say Y here if you want to use the WWAN driver core. This driver
>           provides a common framework for WWAN drivers.
> diff --git a/drivers/net/wwan/wwan_core.c b/drivers/net/wwan/wwan_core.c
> index c735b9830e6e..453ff259809c 100644
> --- a/drivers/net/wwan/wwan_core.c
> +++ b/drivers/net/wwan/wwan_core.c
> @@ -1,5 +1,9 @@
>  // SPDX-License-Identifier: GPL-2.0-only
> -/* Copyright (c) 2021, Linaro Ltd <loic.poulain@...aro.org> */
> +/* WWAN Driver Core
> + *
> + * Copyright (c) 2021, Linaro Ltd <loic.poulain@...aro.org>
> + * Copyright (c) 2025, Sergey Ryazanov <ryazanov.s.a@...il.com>
> + */
>
>  #include <linux/bitmap.h>
>  #include <linux/err.h>
> @@ -16,6 +20,7 @@
>  #include <linux/types.h>
>  #include <linux/uaccess.h>
>  #include <linux/termios.h>
> +#include <linux/gnss.h>
>  #include <linux/wwan.h>
>  #include <net/rtnetlink.h>
>  #include <uapi/linux/wwan.h>
> @@ -71,6 +76,7 @@ struct wwan_device {
>   * @headroom_len: SKB reserved headroom size
>   * @frag_len: Length to fragment packet
>   * @at_data: AT port specific data
> + * @gnss: Pointer to GNSS device associated with this port
>   */
>  struct wwan_port {
>         enum wwan_port_type type;
> @@ -89,9 +95,16 @@ struct wwan_port {
>                         struct ktermios termios;
>                         int mdmbits;
>                 } at_data;
> +               struct gnss_device *gnss;
>         };
>  };
>
> +static int wwan_port_op_start(struct wwan_port *port);
> +static void wwan_port_op_stop(struct wwan_port *port);
> +static int wwan_port_op_tx(struct wwan_port *port, struct sk_buff *skb,
> +                          bool nonblock);
> +static int wwan_wait_tx(struct wwan_port *port, bool nonblock);
> +
>  static ssize_t index_show(struct device *dev, struct device_attribute *attr, char *buf)
>  {
>         struct wwan_device *wwan = to_wwan_dev(dev);
> @@ -340,6 +353,7 @@ static const struct {
>                 .name = "MIPC",
>                 .devsuf = "mipc",
>         },
> +       /* WWAN_PORT_NMEA is exported via the GNSS subsystem */
>  };
>
>  static ssize_t type_show(struct device *dev, struct device_attribute *attr,
> @@ -488,6 +502,124 @@ static void wwan_port_unregister_wwan(struct wwan_port *port)
>         device_del(&port->dev);
>  }
>
> +#if IS_ENABLED(CONFIG_GNSS)
> +static int wwan_gnss_open(struct gnss_device *gdev)
> +{
> +       return wwan_port_op_start(gnss_get_drvdata(gdev));
> +}
> +
> +static void wwan_gnss_close(struct gnss_device *gdev)
> +{
> +       wwan_port_op_stop(gnss_get_drvdata(gdev));
> +}
> +
> +static int wwan_gnss_write(struct gnss_device *gdev, const unsigned char *buf,
> +                          size_t count)
> +{
> +       struct wwan_port *port = gnss_get_drvdata(gdev);
> +       struct sk_buff *skb, *head = NULL, *tail = NULL;
> +       size_t frag_len, remain = count;
> +       int ret;
> +
> +       ret = wwan_wait_tx(port, false);
> +       if (ret)
> +               return ret;
> +
> +       do {
> +               frag_len = min(remain, port->frag_len);
> +               skb = alloc_skb(frag_len + port->headroom_len, GFP_KERNEL);
> +               if (!skb) {
> +                       ret = -ENOMEM;
> +                       goto freeskb;
> +               }
> +               skb_reserve(skb, port->headroom_len);
> +               memcpy(skb_put(skb, frag_len), buf + count - remain, frag_len);
> +
> +               if (!head) {
> +                       head = skb;
> +               } else {
> +                       if (!tail)
> +                               skb_shinfo(head)->frag_list = skb;
> +                       else
> +                               tail->next = skb;
> +
> +                       tail = skb;
> +                       head->data_len += skb->len;
> +                       head->len += skb->len;
> +                       head->truesize += skb->truesize;
> +               }
> +       } while (remain -= frag_len);
> +
> +       ret = wwan_port_op_tx(port, head, false);
> +       if (!ret)
> +               return count;
> +
> +freeskb:
> +       kfree_skb(head);
> +       return ret;
> +}
> +
> +static struct gnss_operations wwan_gnss_ops = {
> +       .open = wwan_gnss_open,
> +       .close = wwan_gnss_close,
> +       .write_raw = wwan_gnss_write,
> +};
> +
> +/* GNSS port specific device registration */
> +static int wwan_port_register_gnss(struct wwan_port *port)
> +{
> +       struct wwan_device *wwandev = to_wwan_dev(port->dev.parent);
> +       struct gnss_device *gdev;
> +       int err;
> +
> +       gdev = gnss_allocate_device(&wwandev->dev);
> +       if (!gdev)
> +               return -ENOMEM;
> +
> +       /* NB: for now we support only NMEA WWAN port type, so hardcode
> +        * the GNSS port type. If more GNSS WWAN port types will be added,
> +        * then we should dynamically mapt WWAN port type to GNSS type.
> +        */
> +       gdev->type = GNSS_TYPE_NMEA;
> +       gdev->ops = &wwan_gnss_ops;
> +       gnss_set_drvdata(gdev, port);
> +
> +       port->gnss = gdev;
> +
> +       err = gnss_register_device(gdev);
> +       if (err) {
> +               gnss_put_device(gdev);
> +               return err;
> +       }
> +
> +       dev_info(&wwandev->dev, "port %s attached\n", dev_name(&gdev->dev));
> +
> +       return 0;
> +}
> +
> +/* GNSS port specific device unregistration */
> +static void wwan_port_unregister_gnss(struct wwan_port *port)
> +{
> +       struct wwan_device *wwandev = to_wwan_dev(port->dev.parent);
> +       struct gnss_device *gdev = port->gnss;
> +
> +       dev_info(&wwandev->dev, "port %s disconnected\n", dev_name(&gdev->dev));
> +
> +       gnss_deregister_device(gdev);
> +       gnss_put_device(gdev);
> +}
> +#else
> +static inline int wwan_port_register_gnss(struct wwan_port *port)
> +{
> +       return -EOPNOTSUPP;
> +}
> +
> +static inline void wwan_port_unregister_gnss(struct wwan_port *port)
> +{
> +       WARN_ON(1);     /* This handler cannot be called */
> +}
> +#endif
> +
>  struct wwan_port *wwan_create_port(struct device *parent,
>                                    enum wwan_port_type type,
>                                    const struct wwan_port_ops *ops,
> @@ -528,7 +660,11 @@ struct wwan_port *wwan_create_port(struct device *parent,
>         dev_set_drvdata(&port->dev, drvdata);
>         device_initialize(&port->dev);
>
> -       err = wwan_port_register_wwan(port);
> +       if (port->type == WWAN_PORT_NMEA)
> +               err = wwan_port_register_gnss(port);
> +       else
> +               err = wwan_port_register_wwan(port);
> +
>         if (err)
>                 goto error_put_device;
>
> @@ -558,7 +694,10 @@ void wwan_remove_port(struct wwan_port *port)
>         wake_up_interruptible(&port->waitqueue);
>         skb_queue_purge(&port->rxq);
>
> -       wwan_port_unregister_wwan(port);
> +       if (port->type == WWAN_PORT_NMEA)
> +               wwan_port_unregister_gnss(port);
> +       else
> +               wwan_port_unregister_wwan(port);
>
>         put_device(&port->dev);
>
> @@ -569,8 +708,15 @@ EXPORT_SYMBOL_GPL(wwan_remove_port);
>
>  void wwan_port_rx(struct wwan_port *port, struct sk_buff *skb)
>  {
> -       skb_queue_tail(&port->rxq, skb);
> -       wake_up_interruptible(&port->waitqueue);
> +       if (port->type == WWAN_PORT_NMEA) {
> +#if IS_ENABLED(CONFIG_GNSS)
> +               gnss_insert_raw(port->gnss, skb->data, skb->len);
> +#endif
> +               consume_skb(skb);
> +       } else {
> +               skb_queue_tail(&port->rxq, skb);
> +               wake_up_interruptible(&port->waitqueue);
> +       }
>  }
>  EXPORT_SYMBOL_GPL(wwan_port_rx);
>
> diff --git a/include/linux/wwan.h b/include/linux/wwan.h
> index a4d6cc0c9f68..1e0e2cb53579 100644
> --- a/include/linux/wwan.h
> +++ b/include/linux/wwan.h
> @@ -19,6 +19,7 @@
>   * @WWAN_PORT_FASTBOOT: Fastboot protocol control
>   * @WWAN_PORT_ADB: ADB protocol control
>   * @WWAN_PORT_MIPC: MTK MIPC diagnostic interface
> + * @WWAN_PORT_NMEA: embedded GNSS receiver with NMEA output
>   *
>   * @WWAN_PORT_MAX: Highest supported port types
>   * @WWAN_PORT_UNKNOWN: Special value to indicate an unknown port type
> @@ -34,6 +35,7 @@ enum wwan_port_type {
>         WWAN_PORT_FASTBOOT,
>         WWAN_PORT_ADB,
>         WWAN_PORT_MIPC,
> +       WWAN_PORT_NMEA,
>
>         /* Add new port types above this line */
>
> --
> 2.25.1
>

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