api,sar: add D-Bus interface to support SAR

Add a new D-Bus interface to support dynamic SAR across multiple platforms.
The new interface exposes methods to configure sar power levels,
handle the communications with the modem, and let the platform
code be agnostic to modem type.

introspection/all.xml

@@ -16,6 +16,7 @@
   <xi:include href="org.freedesktop.ModemManager1.Modem.Location.xml"/>
   <xi:include href="org.freedesktop.ModemManager1.Modem.Time.xml"/>
   <xi:include href="org.freedesktop.ModemManager1.Modem.Firmware.xml"/>
+  <xi:include href="org.freedesktop.ModemManager1.Modem.Sar.xml"/>
   <xi:include href="org.freedesktop.ModemManager1.Modem.Signal.xml"/>
   <xi:include href="org.freedesktop.ModemManager1.Modem.Oma.xml"/>
 

introspection/org.freedesktop.ModemManager1.Modem.Sar.xml

@@ -0,0 +1,66 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+
+<!--
+ ModemManager 1.0 Interface Specification
+
+   Copyright (C) 2020 Google, Inc.
+-->
+
+<node name="/" xmlns:doc="http://www.freedesktop.org/dbus/1.0/doc.dtd">
+
+  <!--
+      org.freedesktop.ModemManager1.Modem.Sar:
+      @short_description: The ModemManager dynamic SAR interface.
+
+      The SAR interface defines operations and properties for dynamic SAR.
+  -->
+  <interface name="org.freedesktop.ModemManager1.Modem.Sar">
+
+    <!--
+        Enable:
+        @enable: %TRUE to enable dynamic SAR and %FALSE to disable it.
+
+        Enable or disable dynamic SAR.
+
+        When enabled, the modem's output power level can be dynamically updated
+        by the host.
+
+        When disabled, the modem's output power level is dynamically updated
+        exclusively by the device.
+    -->
+    <method name="Enable">
+      <arg name="enable" type="b" direction="in" />
+    </method>
+
+    <!--
+        SetPowerLevel:
+        @level: Index of the SAR power level mapping table.
+
+        Set current dynamic SAR power level for all antennas on the device.
+
+        Please check with your modem vendor for detailed description on the
+        number of levels and corresponding power output for each level.
+
+        The index set here will apply to all antennas on the system.
+    -->
+    <method name="SetPowerLevel">
+      <arg name="level" type="u" direction="in" />
+    </method>
+
+    <!--
+        State:
+
+        Boolean indicating whether dynamic SAR is currently enabled.
+    -->
+    <property name="State" type="b" access="read" />
+
+    <!--
+        PowerLevel:
+
+        Current index of the SAR power level mapping table that is being used
+        for setting the output power of all antennas on the system.
+    -->
+    <property name="PowerLevel" type="u" access="read" />
+
+  </interface>
+</node>