monitors/alsa: provide splitting of UCM SplitPCM nodes

Instruct ACP to provide information about UCM SplitPCM channel
splitting instead of doing it with alsa-lib plugins.

Use the provided information to load loopbacks that create virtual sinks
that do the channel remapping from UCM.

src/scripts/monitors/alsa.lua

@@ -5,6 +5,9 @@
 --
 -- SPDX-License-Identifier: MIT
 
+SPLIT_PCM_PARENT_OFFSET = 256
+SPLIT_PCM_OFFSET = 512
+
 cutils = require ("common-utils")
 log = Log.open_topic ("s-monitors")
 
@@ -30,8 +33,150 @@ function applyDefaultDeviceProperties (properties)
   properties["api.acp.auto-profile"] = false
   properties["api.acp.auto-port"] = false
   properties["api.dbus.ReserveDevice1.Priority"] = -20
+  properties["api.alsa.split-enable"] = true
 end
 
+function createSplitPCMHWNode(dev_props, properties)
+  local skip_keys = {
+    "api.alsa.split.position", "card.profile.device", "device.profile.description",
+    "device.profile.name"
+  }
+  local props = {}
+
+  for k, v in pairs(properties) do
+    props[k] = v
+  end
+  for _, k in pairs(skip_keys) do
+    props[k] = nil
+  end
+
+  -- create the underlying hidden ALSA node
+  props["node.name"] = props["api.alsa.split.name"]
+  props["node.description"] = string.format("%s %s", dev_props["device.description"],
+        props["api.alsa.path"]:gsub("^[^,]*[,:]", ""))
+  if props["api.alsa.pcm.stream"] == "capture" then
+    props["media.class"] = "Audio/Source/Internal"
+  else
+    props["media.class"] = "Audio/Sink/Internal"
+  end
+  props["api.alsa.use-chmap"] = false
+  props["api.alsa.split.parent"] = true
+  props["audio.position"] = props["api.alsa.split.hw-position"]
+  local channels = Json.Raw (props["api.alsa.split.hw-position"]):parse ()
+  props["audio.channels"] = tostring(#channels)
+
+  props = JsonUtils.match_rules_update_properties (config.rules, props)
+
+  if cutils.parseBool (props ["node.disabled"]) then
+    log:notice ("ALSA node " .. props ["node.name"] .. " disabled")
+    return nil
+  end
+
+  return Node("adapter", props)
+end
+
+function createSplitPCMLoopback(parent, id, obj_type, factory, properties)
+  local skip_keys = {
+    -- not suitable for loopback
+    "audio.rate",
+    "clock.quantum-limit",
+    "factory.name",
+    "node.driver",
+    "node.pause-on-idle",
+    "node.want-driver",
+    "port.group",
+    "priority.driver",
+    "resample.disable",
+    "resample.prefill",
+  }
+  local args
+  local props = {}
+
+  props["node.virtual"] = false
+
+  for k, v in pairs(properties) do
+    props[k] = v
+  end
+  for _, k in pairs(skip_keys) do
+    props[k] = nil
+  end
+
+  local split_props = {
+    ["node.name"] = properties["node.name"] .. ".split",
+    ["node.description"] = string.format(I18n.gettext("Split %s"), properties["node.description"]),
+    ["audio.position"] = properties["api.alsa.split.position"],
+    ["stream.dont-remix"] = true,
+    ["node.passive"] = true,
+    ["node.dont-fallback"] = true,
+    ["node.linger"] = true,
+    ["target.object"] = properties["api.alsa.split.name"],
+  }
+
+  if properties["api.alsa.pcm.stream"] == "playback" then
+    props["media.class"] = "Audio/Sink"
+    split_props["media.class"] = "Stream/Output/Audio/Internal"
+    args = Json.Object {
+      ["capture.props"] = Json.Object (props),
+      ["playback.props"] = Json.Object (split_props),
+    }
+  else
+    props["media.class"] = "Audio/Source"
+    split_props["media.class"] = "Stream/Input/Audio/Internal"
+    args = Json.Object {
+      ["playback.props"] = Json.Object (props),
+      ["capture.props"] = Json.Object (split_props),
+    }
+  end
+
+  return LocalModule("libpipewire-module-loopback", args:get_data(), {})
+end
+
+devices_om = ObjectManager {
+  Interest {
+    type = "device",
+  }
+}
+
+split_nodes_om = ObjectManager {
+  Interest {
+    type = "node",
+    Constraint { "api.alsa.split.position", "+", type = "pw" },
+  }
+}
+
+split_nodes_om:connect ("object-added", function(_, node)
+    -- Connect ObjectConfig events to the right node
+    if not monitor then
+      return
+    end
+
+    local interest = Interest {
+      type = "device",
+      Constraint { "object.id", "=", node.properties["device.id"] }
+    }
+    log:info("Split PCM node found: " .. tostring (node["bound-id"]))
+
+    for device in devices_om:iterate (interest) do
+      local device_id = device.properties["spa.object.id"]
+      if not device_id then
+        goto next_device
+      end
+
+      local spa_device = monitor:get_managed_object (tonumber (device_id))
+      if not spa_device then
+        goto next_device
+      end
+
+      local id = node.properties["card.profile.device"]
+      if id ~= nil then
+        log:info(".. assign to device: " .. tostring (device["bound-id"]) .. " node " .. tostring (id))
+        spa_device:store_managed_object (id, node)
+      end
+
+      ::next_device::
+    end
+end)
+
 function createNode(parent, id, obj_type, factory, properties)
   local dev_props = parent.properties
   local parent_id = tonumber(dev_props["spa.object.id"])
@@ -161,6 +306,10 @@ function createNode(parent, id, obj_type, factory, properties)
   end
 
   -- apply properties from rules defined in JSON .conf file
+  local orig_properties = {}
+  for k, v in pairs(properties) do
+    orig_properties[k] = v
+  end
   properties = JsonUtils.match_rules_update_properties (config.rules, properties)
 
   if cutils.parseBool (properties ["node.disabled"]) then
@@ -171,6 +320,36 @@ function createNode(parent, id, obj_type, factory, properties)
   node_names_table[properties["node.name"]] = true
   id_name_table[parent_id][id] = properties["node.name"]
 
+  -- handle split HW node
+  if properties["api.alsa.split.position"] ~= nil then
+    local split_hw_node_name = string.format("%s.%s",
+      (stream == "capture" and "alsa_input" or "alsa_output"),
+      properties["api.alsa.path"]:gsub("([:,])", "_"))
+    properties["api.alsa.split.name"] = split_hw_node_name
+    orig_properties["api.alsa.split.name"] = split_hw_node_name
+
+    if not node_names_table [split_hw_node_name] then
+      log:info ("Create ALSA SplitPCM HW node " .. split_hw_node_name)
+
+      local node = createSplitPCMHWNode(dev_props, orig_properties)
+      if node ~= nil then
+        node:activate(Feature.Proxy.BOUND)
+        parent:store_managed_object(SPLIT_PCM_PARENT_OFFSET + id, node)
+
+        node_names_table[split_hw_node_name] = true
+        id_name_table[parent_id][SPLIT_PCM_PARENT_OFFSET + id] = split_hw_node_name
+      end
+    end
+
+    -- create split PCM node
+    log:info ("Create ALSA SplitPCM split node " .. properties["node.name"])
+
+    local loopback = createSplitPCMLoopback (parent, id, obj_type, factory, properties)
+    parent:store_managed_object(SPLIT_PCM_OFFSET + id, loopback)
+    parent:set_managed_pending(id)
+    return
+  end
+
   -- create the node
   local node = Node("adapter", properties)
   node:activate(Feature.Proxy.BOUND, function (_, err)
@@ -184,12 +363,18 @@ end
 
 function removeNode(parent, id)
   local parent_id = tonumber(parent.properties["spa.object.id"])
-  local node_name = id_name_table[parent_id][id]
+  local ids = {id, SPLIT_PCM_PARENT_OFFSET + id, SPLIT_PCM_OFFSET + id}
 
-  if node_name ~= nil then
-    log:info ("Removing node " .. node_name)
-    node_names_table[node_name] = nil
-    id_name_table[parent_id][id] = nil
+  for _, j in pairs(ids) do
+    local node_name = id_name_table[parent_id][j]
+
+    parent:store_managed_object(j, nil)
+
+    if node_name ~= nil then
+      log:info ("Removing node " .. node_name)
+      node_names_table[node_name] = nil
+      id_name_table[parent_id][j] = nil
+    end
   end
 end
 
@@ -421,3 +606,6 @@ end
 
 -- create the monitor
 monitor = createMonitor()
+
+devices_om:activate()
+split_nodes_om:activate()