bluez: Add Offload SCO nodes

For offload SCO, the audio stream should be routed to/from Bluetooth
chipset via ALSA.
To do this, this commit prevent the creation of the sco-source or sco-sink
nodes, and replace them by loopback nodes.
It's up to the platform to correctly the the route to the Bluetooth chipset
ALSA entries.

When the loopback node state change to running, the script also call the
bluetoothOffloadActive param of the device to start/stop the SCO link.

src/config/bluetooth.lua.d/50-bluez-config.lua

@@ -34,6 +34,9 @@ bluez_monitor.properties = {
   --   'Device' property of org.freedesktop.ModemManager1.Modem interface
   --["bluez5.hfphsp-backend-native-modem"] = "none",
 
+  -- HFP/HSP hardware offload SCO support (default: false).
+  --["bluez5.hw-offload-sco"] = false,
+
   -- Properties for the A2DP codec configuration
   --["bluez5.default.rate"] = 48000,
   --["bluez5.default.channels"] = 2,

src/scripts/monitors/bluez.lua

@@ -7,6 +7,20 @@
 
 local config = ... or {}
 
+devices_om = ObjectManager {
+  Interest {
+    type = "device",
+  }
+}
+
+nodes_om = ObjectManager {
+  Interest {
+    type = "node",
+    Constraint { "node.name", "#", "*.bluez_*put*"},
+    Constraint { "device.id", "+" },
+  }
+}
+
 -- preprocess rules and create Interest objects
 for _, r in ipairs(config.rules or {}) do
   r.interests = {}
@@ -37,9 +51,105 @@ function rulesApplyProperties(properties)
   end
 end
 
+function setOffloadActive(device, value)
+  local pod = Pod.Object {
+    "Spa:Pod:Object:Param:Props", "Props", bluetoothOffloadActive = value
+  }
+  device:set_params("Props", pod)
+end
+
+nodes_om:connect("object-added", function(_, node)
+  node:connect("state-changed", function(node, old_state, cur_state)
+    local interest = Interest {
+      type = "device",
+      Constraint { "object.id", "=", node.properties["device.id"]}
+    }
+    for d in devices_om:iterate (interest) do
+      if cur_state == "running" then
+        setOffloadActive(d, true)
+      else
+        setOffloadActive(d, false)
+      end
+    end
+  end)
+end)
+
+function createOffloadScoNode(parent, id, type, factory, properties)
+  local dev_props = parent.properties
+
+  local args = {
+    ["audio.channels"] = 1,
+    ["audio.position"] = "[MONO]",
+  }
+
+  local desc =
+      dev_props["device.description"]
+      or dev_props["device.name"]
+      or dev_props["device.nick"]
+      or dev_props["device.alias"]
+      or "bluetooth-device"
+  -- sanitize description, replace ':' with ' '
+  args["node.description"] = desc:gsub("(:)", " ")
+
+  if factory:find("sink") then
+    local capture_args = {
+      ["device.id"] = parent["bound-id"],
+      ["media.class"] = "Audio/Sink",
+      ["node.pause-on-idle"] = false,
+    }
+    for k, v in pairs(properties) do
+      capture_args[k] = v
+    end
+
+    local name = "bluez_output" .. "." .. (properties["api.bluez5.address"] or dev_props["device.name"]) .. "." .. tostring(id)
+    args["node.name"] = name:gsub("([^%w_%-%.])", "_")
+    args["capture.props"] = Json.Object(capture_args)
+    args["playback.props"] = Json.Object {
+      ["node.passive"] = true,
+      ["node.pause-on-idle"] = false,
+    }
+  elseif factory:find("source") then
+    local playback_args = {
+      ["device.id"] = parent["bound-id"],
+      ["media.class"] = "Audio/Source",
+      ["node.pause-on-idle"] = false,
+    }
+    for k, v in pairs(properties) do
+      playback_args[k] = v
+    end
+
+    local name = "bluez_input" .. "." .. (properties["api.bluez5.address"] or dev_props["device.name"]) .. "." .. tostring(id)
+    args["node.name"] = name:gsub("([^%w_%-%.])", "_")
+    args["capture.props"] = Json.Object {
+      ["node.passive"] = true,
+      ["node.pause-on-idle"] = false,
+    }
+    args["playback.props"] = Json.Object(playback_args)
+  else
+    Log.warning(parent, "Unsupported factory: " .. factory)
+    return
+  end
+
+  -- Transform 'args' to a json object here
+  local args_json = Json.Object(args)
+
+  -- and get the final JSON as a string from the json object
+  local args_string = args_json:get_data()
+
+  local loopback_properties = {}
+
+  local loopback = LocalModule("libpipewire-module-loopback", args_string, loopback_properties)
+  parent:store_managed_object(id, loopback)
+end
+
 function createNode(parent, id, type, factory, properties)
   local dev_props = parent.properties
 
+  if config.properties["bluez5.hw-offload-sco"] and factory:find("sco") then
+    createOffloadScoNode(parent, id, type, factory, properties)
+    return
+  end
+
   -- set the device id and spa factory name; REQUIRED, do not change
   properties["device.id"] = parent["bound-id"]
   properties["factory.name"] = factory
@@ -192,3 +302,6 @@ if logind_plugin then
 else
   monitor = createMonitor()
 end
+
+nodes_om:activate()
+devices_om:activate()