Support modem discovery via automatic modem implementation

README.md

@@ -79,6 +79,56 @@ Here's an example with a service provider list:
   }
 ```
 
+## Automatic modem detection
+
+If it is not known ahead of time what modem will be installed, the
+`VintageNetMobile.Modem.Automatic` implementation can detect and configure it
+for you. It works by waiting for the system to report a USB device with a known
+vendor and product ID. Once one is found, it calls `VintageNet.configure/3` to
+change the configuration from using the `Automatic` modem to the actual modem
+implementation. It tells `VintageNet.configure/3` to not persist the
+configuration so that the detection process runs again on the next boot.
+
+Here's an example:
+
+```elixir
+  %{
+    type: VintageNetMobile,
+    vintage_net_mobile: %{
+      modem: VintageNetMobile.Modem.Automatic,
+      service_providers: [
+        %{apn: "wireless.twilio.com"}
+      ]
+    }
+  }
+```
+
+See [VintageNetMobile.Modem.Automatic.Discovery](lib/vintage_net_mobile/modem/automatic/discovery.ex)
+for a list of modems that can be detected.
+
+To check if your modem has been detected correctly you can run
+`VintageNet.info()` and check the output configuration's `:modem` field:
+
+```elixir
+iex> VintageNet.info()
+Interface ppp0
+  Type: VintageNetMobile
+  Power: Starting up/on (248378 ms left)
+  Present: true
+  State: :configured (0:01:13)
+  Connection: :internet (21.8 s)
+  Addresses: 111.11.111.111/32
+  Configuration:
+    %{
+      type: VintageNetMobile,
+      vintage_net_mobile: %{
+        modem: VintageNetMobile.Modem.TelitLE910,
+        service_providers: [%{apn: "thebestapn"}]
+      }
+    }
+
+```
+
 ## VintageNet Properties
 
 In addition to the common `vintage_net` properties for all interface types, this

lib/vintage_net_mobile/modem/automatic.ex

@@ -0,0 +1,27 @@
+defmodule VintageNetMobile.Modem.Automatic do
+  @moduledoc """
+  Modem for automatic detection and configuration of USB-based modems
+
+  This is useful for when you need to support different types of modems and you
+  cannot provide a static configuration for one particular modem.
+  """
+  @behaviour VintageNetMobile.Modem
+
+  alias VintageNet.Interface.RawConfig
+  alias VintageNetMobile.Modem.Automatic.Discovery
+
+  @impl VintageNetMobile.Modem
+  def normalize(config), do: config
+
+  @impl VintageNetMobile.Modem
+  def add_raw_config(raw_config, %{vintage_net_mobile: _mobile}, _opts) do
+    child_specs = [
+      {Discovery, [raw_config: raw_config]}
+    ]
+
+    %RawConfig{
+      raw_config
+      | child_specs: child_specs
+    }
+  end
+end

lib/vintage_net_mobile/modem/automatic/discovery.ex

@@ -0,0 +1,96 @@
+defmodule VintageNetMobile.Modem.Automatic.Discovery do
+  @moduledoc false
+
+  # A process for trying to discover a the type of modem and some basic
+  # information to allow dynamic configuration items
+
+  use GenServer
+
+  alias Circuits.UART
+
+  # the poll time for trying to enumerate the UARTS
+  @enumeration_poll 3_000
+
+  # To discover a which modem to use this process looks at the vendor ids and
+  # manufacturer id to map to a `VintageNetMobile.Modem` implementation.
+
+  # A source to find vendor and manufacturer ids is
+  # https://elixir.bootlin.com/linux/latest/source/drivers/usb/serial/option.c#L245
+
+  @quectel_vender_id 0x2C7C
+  @telit_vendor_id 0x1BC7
+
+  @modems %{
+    {@telit_vendor_id, 0x1201} => VintageNetMobile.Modem.TelitLE910,
+    {@quectel_vender_id, 0x0125} => VintageNetMobile.Modem.QuectelEC25,
+    # map the EC21 to the EC25 as they work the same
+    {@quectel_vender_id, 0x0121} => VintageNetMobile.Modem.QuectelEC25,
+    {@quectel_vender_id, 0x0296} => VintageNetMobile.Modem.QuectelBG96
+  }
+
+  @typedoc """
+  Init args
+
+  - `:raw_config` - The RawConfig that contains configuration information to
+    pass the discovered modem
+  """
+  @type init_arg() :: {:raw_config, VintageNet.Interface.RawConfig.t()}
+
+  @doc """
+  Start the discovery server
+  """
+  @spec start_link([init_arg()]) :: GenServer.on_start()
+  def start_link(args) do
+    GenServer.start_link(__MODULE__, args, name: __MODULE__)
+  end
+
+  @impl GenServer
+  def init(args) do
+    {:ok, %{modem: nil, raw_config: args[:raw_config]}, {:continue, :detect_modem}}
+  end
+
+  @impl GenServer
+  def handle_continue(:detect_modem, state) do
+    {:noreply, do_detect_modem(state)}
+  end
+
+  @impl GenServer
+  def handle_info(:detect_modem, state) do
+    {:noreply, do_detect_modem(state)}
+  end
+
+  defp do_detect_modem(state) do
+    case detect_modem() do
+      nil ->
+        Process.send_after(self(), :detect_modem, @enumeration_poll)
+        state
+
+      modem ->
+        state = %{state | modem: modem}
+        :ok = configure_vintage_net(state)
+
+        state
+    end
+  end
+
+  defp configure_vintage_net(state) do
+    config = state.raw_config.source_config.vintage_net_mobile |> Map.put(:modem, state.modem)
+
+    VintageNet.configure(
+      state.raw_config.ifname,
+      %{type: VintageNetMobile, vintage_net_mobile: config},
+      persist: false
+    )
+  end
+
+  defp detect_modem() do
+    UART.enumerate()
+    |> Enum.find_value(&known_modem/1)
+  end
+
+  defp known_modem({_tty, %{vendor_id: vid, product_id: pid}}) do
+    Map.get(@modems, {vid, pid})
+  end
+
+  defp known_modem(_), do: nil
+end

test/vintage_net_mobile/modem/automatic_test.exs

@@ -0,0 +1,49 @@
+defmodule VintageNetMobile.Modem.AutomaticTest do
+  use ExUnit.Case, async: true
+
+  alias VintageNetMobile.Modem.Automatic
+  alias VintageNetMobile.Modem.Automatic.Discovery
+  alias VintageNet.Interface.RawConfig
+
+  test "create LTE configuration" do
+    input = %{
+      type: VintageNetMobile,
+      vintage_net_mobile: %{
+        modem: Automatic,
+        service_providers: [%{apn: "choosethislteitissafe"}, %{apn: "wireless.twilio.com"}]
+      }
+    }
+
+    # RawConfig that will be passed to the discovered modem
+    base_raw_config = %RawConfig{
+      ifname: "ppp0",
+      type: VintageNetMobile,
+      source_config: input,
+      required_ifnames: ["wwan0"],
+      up_cmds: [],
+      down_cmds: [],
+      files: [],
+      child_specs: []
+    }
+
+    output = %RawConfig{
+      ifname: "ppp0",
+      type: VintageNetMobile,
+      source_config: input,
+      required_ifnames: ["wwan0"],
+      up_cmds: [
+        {:run_ignore_errors, "mknod", ["/dev/ppp", "c", "108", "0"]}
+      ],
+      down_cmds: [
+        {:fun, VintageNet.PropertyTable, :clear_prefix,
+         [VintageNet, ["interface", "ppp0", "mobile"]]}
+      ],
+      files: [],
+      child_specs: [
+        {Discovery, [raw_config: base_raw_config]}
+      ]
+    }
+
+    assert output == VintageNetMobile.to_raw_config("ppp0", input, Utils.default_opts())
+  end
+end