From 65a81cee47c937cf07d70f8717d2f6225135b9f8 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Wed, 21 Aug 2024 22:35:57 -0700
Subject: [PATCH] power: Add LowPowerMode1 service

Add a new service to limit the platform TDP while handles are still held. This
feature is currently limited to the Steam Deck.
---
 com.steampowered.SteamOSManager1.xml |  36 +++
 data/platforms/jupiter.toml          |   1 +
 src/bin/steamosctl.rs                |  15 +-
 src/daemon/user.rs                   |  17 +-
 src/manager/root.rs                  |  11 +-
 src/manager/user.rs                  | 197 ++++++++++---
 src/platform.rs                      |   2 +
 src/power.rs                         | 414 ++++++++++++++++++++++++++-
 src/proxy/low_power_mode1.rs         |  27 ++
 src/proxy/mod.rs                     |   2 +
 10 files changed, 666 insertions(+), 56 deletions(-)
 create mode 100644 src/proxy/low_power_mode1.rs

diff --git a/com.steampowered.SteamOSManager1.xml b/com.steampowered.SteamOSManager1.xml
index 7207e2e..e32e03b 100644
--- a/com.steampowered.SteamOSManager1.xml
+++ b/com.steampowered.SteamOSManager1.xml
@@ -206,6 +206,42 @@
 
   </interface>
 
+  <!--
+      com.steampowered.SteamOSManager1.LowPowerMode1
+      @short_description: Interface for handling a low power mode.
+  -->
+  <interface name="com.steampowered.SteamOSManager1.LowPowerMode1">
+
+    <!--
+        EnterDownloadMode:
+
+        Enter a low power mode for downloads and get a handle that will keep
+        this mode active until all obtained handles are dropped.
+
+        @identifier: A human-readable string to identify who has obtained this handle.
+        @handle: A file handle that must be retained to keep download mode
+        active. When all handles are closed, low power mode is exited.
+    -->
+    <method name="EnterDownloadMode">
+      <arg type="s" name="identifier" direction="in"/>
+      <arg type="h" name="handle" direction="out"/>
+    </method>
+
+    <!--
+        ListDownloadModeHandles
+
+        Get a list of all of the currently open download mode handles.
+
+        @identifiers: A dict of all open download mode handles, as a pair of
+        the identifier passed to EnterDownloadMode and the number of handles
+        requested for that identifier.
+    -->
+    <method name="ListDownloadModeHandles">
+      <arg type="a{su}" name="identifiers" direction="out"/>
+    </method>
+
+  </interface>
+
   <!--
       com.steampowered.SteamOSManager1.Manager2
       @short_description: Interface for basic manager control.
diff --git a/data/platforms/jupiter.toml b/data/platforms/jupiter.toml
index f7981c9..881ebb8 100644
--- a/data/platforms/jupiter.toml
+++ b/data/platforms/jupiter.toml
@@ -31,6 +31,7 @@ systemd = "jupiter-fan-control.service"
 
 [tdp_limit]
 method = "gpu_hwmon"
+download_mode_limit = 6
 
 [tdp_limit.range]
 min = 3
diff --git a/src/bin/steamosctl.rs b/src/bin/steamosctl.rs
index ef2c65c..e437ce1 100644
--- a/src/bin/steamosctl.rs
+++ b/src/bin/steamosctl.rs
@@ -16,8 +16,9 @@ use steamos_manager::power::{CPUScalingGovernor, GPUPerformanceLevel, GPUPowerPr
 use steamos_manager::proxy::{
     AmbientLightSensor1Proxy, BatteryChargeLimit1Proxy, CpuScaling1Proxy, FactoryReset1Proxy,
     FanControl1Proxy, GpuPerformanceLevel1Proxy, GpuPowerProfile1Proxy, HdmiCec1Proxy,
-    Manager2Proxy, PerformanceProfile1Proxy, Storage1Proxy, TdpLimit1Proxy, UpdateBios1Proxy,
-    UpdateDock1Proxy, WifiDebug1Proxy, WifiDebugDump1Proxy, WifiPowerManagement1Proxy,
+    LowPowerMode1Proxy, Manager2Proxy, PerformanceProfile1Proxy, Storage1Proxy, TdpLimit1Proxy,
+    UpdateBios1Proxy, UpdateDock1Proxy, WifiDebug1Proxy, WifiDebugDump1Proxy,
+    WifiPowerManagement1Proxy,
 };
 use steamos_manager::wifi::{WifiBackend, WifiDebugMode, WifiPowerManagement};
 use zbus::fdo::{IntrospectableProxy, PropertiesProxy};
@@ -170,6 +171,9 @@ enum Commands {
         state: HdmiCecState,
     },
 
+    /// List active low power download mode handles
+    ListLowPowerDownloadModeHandles,
+
     /// Update the BIOS, if possible
     UpdateBios,
 
@@ -468,6 +472,13 @@ async fn main() -> Result<()> {
                 Err(_) => println!("Got unknown value {state} from backend"),
             }
         }
+        Commands::ListLowPowerDownloadModeHandles => {
+            let proxy = LowPowerMode1Proxy::new(&conn).await?;
+            let handles: HashMap<String, u32> = proxy.list_download_mode_handles().await?;
+            for (identifier, count) in handles.into_iter().sorted() {
+                println!("{identifier}: {count}");
+            }
+        }
         Commands::UpdateBios => {
             let proxy = UpdateBios1Proxy::new(&conn).await?;
             let _ = proxy.update_bios().await?;
diff --git a/src/daemon/user.rs b/src/daemon/user.rs
index b8a1237..cd30ef0 100644
--- a/src/daemon/user.rs
+++ b/src/daemon/user.rs
@@ -20,8 +20,8 @@ use crate::daemon::{channel, Daemon, DaemonCommand, DaemonContext};
 use crate::job::{JobManager, JobManagerService};
 use crate::manager::user::create_interfaces;
 use crate::path;
+use crate::power::TdpManagerService;
 use crate::udev::UdevMonitor;
-use crate::Service;
 
 #[derive(Copy, Clone, Default, Deserialize, Debug)]
 #[serde(default)]
@@ -104,7 +104,7 @@ pub(crate) type Command = DaemonCommand<()>;
 
 async fn create_connections(
     channel: Sender<Command>,
-) -> Result<(Connection, Connection, impl Service)> {
+) -> Result<(Connection, Connection, JobManagerService, TdpManagerService)> {
     let system = Connection::system().await?;
     let connection = Builder::session()?
         .name("com.steampowered.SteamOSManager1")?
@@ -113,10 +113,14 @@ async fn create_connections(
 
     let (jm_tx, rx) = unbounded_channel();
     let job_manager = JobManager::new(connection.clone()).await?;
-    let service = JobManagerService::new(job_manager, rx, system.clone());
-    create_interfaces(connection.clone(), system.clone(), channel, jm_tx).await?;
+    let jm_service = JobManagerService::new(job_manager, rx, system.clone());
 
-    Ok((connection, system, service))
+    let (tdp_tx, rx) = unbounded_channel();
+    let tdp_service = TdpManagerService::new(rx, &system).await?;
+
+    create_interfaces(connection.clone(), system.clone(), channel, jm_tx, tdp_tx).await?;
+
+    Ok((connection, system, jm_service, tdp_service))
 }
 
 pub async fn daemon() -> Result<()> {
@@ -127,7 +131,7 @@ pub async fn daemon() -> Result<()> {
     let subscriber = Registry::default().with(stdout_log);
     let (tx, rx) = channel::<UserContext>();
 
-    let (session, system, mirror_service) = match create_connections(tx).await {
+    let (session, system, mirror_service, tdp_service) = match create_connections(tx).await {
         Ok(c) => c,
         Err(e) => {
             let _guard = tracing::subscriber::set_default(subscriber);
@@ -140,6 +144,7 @@ pub async fn daemon() -> Result<()> {
     let mut daemon = Daemon::new(subscriber, system, rx).await?;
 
     daemon.add_service(mirror_service);
+    daemon.add_service(tdp_service);
 
     daemon.run(context).await
 }
diff --git a/src/manager/root.rs b/src/manager/root.rs
index 619b57a..48260d3 100644
--- a/src/manager/root.rs
+++ b/src/manager/root.rs
@@ -15,7 +15,7 @@ use tokio::sync::oneshot;
 use tracing::{error, info};
 use zbus::object_server::SignalEmitter;
 use zbus::zvariant::{self, Fd};
-use zbus::{fdo, interface, Connection};
+use zbus::{fdo, interface, proxy, Connection};
 
 use crate::daemon::root::{Command, RootCommand};
 use crate::daemon::DaemonCommand;
@@ -91,6 +91,15 @@ impl SteamOSManager {
     }
 }
 
+#[proxy(
+    interface = "com.steampowered.SteamOSManager1.RootManager",
+    default_service = "com.steampowered.SteamOSManager1",
+    default_path = "/com/steampowered/SteamOSManager1"
+)]
+pub(crate) trait RootManager {
+    fn set_tdp_limit(&self, limit: u32) -> zbus::Result<()>;
+}
+
 #[interface(name = "com.steampowered.SteamOSManager1.RootManager")]
 impl SteamOSManager {
     async fn prepare_factory_reset(&self, kind: u32) -> fdo::Result<u32> {
diff --git a/src/manager/user.rs b/src/manager/user.rs
index ed4aa1a..a8e40d3 100644
--- a/src/manager/user.rs
+++ b/src/manager/user.rs
@@ -6,13 +6,14 @@
  * SPDX-License-Identifier: MIT
  */
 
-use anyhow::Result;
+use anyhow::{Error, Result};
 use std::collections::HashMap;
 use tokio::sync::mpsc::{Sender, UnboundedSender};
 use tokio::sync::oneshot;
 use tracing::error;
 use zbus::object_server::SignalEmitter;
 use zbus::proxy::{Builder, CacheProperties};
+use zbus::zvariant::Fd;
 use zbus::{fdo, interface, zvariant, Connection, ObjectServer, Proxy};
 
 use crate::cec::{HdmiCecControl, HdmiCecState};
@@ -28,7 +29,7 @@ use crate::power::{
     get_available_cpu_scaling_governors, get_available_gpu_performance_levels,
     get_available_gpu_power_profiles, get_available_platform_profiles, get_cpu_scaling_governor,
     get_gpu_clocks, get_gpu_clocks_range, get_gpu_performance_level, get_gpu_power_profile,
-    get_max_charge_level, get_platform_profile, tdp_limit_manager, TdpLimitManager,
+    get_max_charge_level, get_platform_profile, tdp_limit_manager, TdpManagerCommand,
 };
 use crate::wifi::{
     get_wifi_backend, get_wifi_power_management_state, list_wifi_interfaces, WifiBackend,
@@ -131,14 +132,17 @@ struct GpuPowerProfile1 {
 }
 
 struct TdpLimit1 {
-    proxy: Proxy<'static>,
-    manager: Box<dyn TdpLimitManager>,
+    manager: UnboundedSender<TdpManagerCommand>,
 }
 
 struct HdmiCec1 {
     hdmi_cec: HdmiCecControl<'static>,
 }
 
+struct LowPowerMode1 {
+    manager: UnboundedSender<TdpManagerCommand>,
+}
+
 struct Manager2 {
     proxy: Proxy<'static>,
     channel: Sender<Command>,
@@ -146,7 +150,7 @@ struct Manager2 {
 
 struct PerformanceProfile1 {
     proxy: Proxy<'static>,
-    tdp_limit_manager: Option<Box<dyn TdpLimitManager>>,
+    tdp_limit_manager: UnboundedSender<TdpManagerCommand>,
 }
 
 struct Storage1 {
@@ -444,6 +448,39 @@ impl HdmiCec1 {
     }
 }
 
+#[interface(name = "com.steampowered.SteamOSManager1.LowPowerMode1")]
+impl LowPowerMode1 {
+    async fn enter_download_mode(&self, identifier: &str) -> fdo::Result<Fd> {
+        let (tx, rx) = oneshot::channel();
+        self.manager
+            .send(TdpManagerCommand::EnterDownloadMode(
+                identifier.to_string(),
+                tx,
+            ))
+            .map_err(|_| {
+                fdo::Error::Failed(String::from("Failed to obtain download mode handle"))
+            })?;
+        Ok(rx
+            .await
+            .map_err(to_zbus_fdo_error)?
+            .map_err(to_zbus_fdo_error)?
+            .ok_or(fdo::Error::Failed(String::from(
+                "Download mode not configured",
+            )))?
+            .into())
+    }
+
+    async fn list_download_mode_handles(&self) -> fdo::Result<HashMap<String, u32>> {
+        let (tx, rx) = oneshot::channel();
+        self.manager
+            .send(TdpManagerCommand::ListDownloadModeHandles(tx))
+            .map_err(|_| {
+                fdo::Error::Failed(String::from("Failed to obtain download mode handle list"))
+            })?;
+        rx.await.map_err(to_zbus_fdo_error)
+    }
+}
+
 #[interface(name = "com.steampowered.SteamOSManager1.Manager2")]
 impl Manager2 {
     async fn reload_config(&self) -> fdo::Result<()> {
@@ -499,22 +536,25 @@ impl PerformanceProfile1 {
         #[zbus(connection)] connection: &Connection,
     ) -> zbus::Result<()> {
         let _: () = self.proxy.call("SetPerformanceProfile", &(profile)).await?;
-        if self.tdp_limit_manager.is_some() {
-            let connection = connection.clone();
-            let manager = tdp_limit_manager().await.map_err(to_zbus_error)?;
-            let proxy = self.proxy.clone();
-            tokio::spawn(async move {
-                if manager.is_active().await.map_err(to_zbus_error)? {
-                    let tdp_limit = TdpLimit1 { proxy, manager };
-                    connection.object_server().at(MANAGER_PATH, tdp_limit).await
-                } else {
-                    connection
-                        .object_server()
-                        .remove::<TdpLimit1, _>(MANAGER_PATH)
-                        .await
-                }
-            });
-        }
+        let connection = connection.clone();
+        let manager = self.tdp_limit_manager.clone();
+        let _ = manager.send(TdpManagerCommand::UpdateDownloadMode);
+        tokio::spawn(async move {
+            let (tx, rx) = oneshot::channel();
+            manager.send(TdpManagerCommand::IsActive(tx))?;
+            Ok::<(), Error>(if rx.await?? {
+                let tdp_limit = TdpLimit1 { manager };
+                connection
+                    .object_server()
+                    .at(MANAGER_PATH, tdp_limit)
+                    .await?;
+            } else {
+                connection
+                    .object_server()
+                    .remove::<TdpLimit1, _>(MANAGER_PATH)
+                    .await?;
+            })
+        });
         Ok(())
     }
 
@@ -551,30 +591,56 @@ impl Storage1 {
 impl TdpLimit1 {
     #[zbus(property(emits_changed_signal = "false"))]
     async fn tdp_limit(&self) -> u32 {
-        self.manager.get_tdp_limit().await.unwrap_or(0)
+        let (tx, rx) = oneshot::channel();
+        if self
+            .manager
+            .send(TdpManagerCommand::GetTdpLimit(tx))
+            .is_err()
+        {
+            return 0;
+        }
+        rx.await.unwrap_or(Ok(0)).unwrap_or(0)
     }
 
     #[zbus(property)]
     async fn set_tdp_limit(&self, limit: u32) -> zbus::Result<()> {
-        self.proxy.call("SetTdpLimit", &(limit)).await
+        self.manager
+            .send(TdpManagerCommand::SetTdpLimit(limit))
+            .map_err(|_| zbus::Error::Failure(String::from("Failed to set TDP limit")))
     }
 
     #[zbus(property(emits_changed_signal = "const"))]
     async fn tdp_limit_min(&self) -> u32 {
-        self.manager
-            .get_tdp_limit_range()
-            .await
-            .map(|r| *r.start())
-            .unwrap_or(0)
+        let (tx, rx) = oneshot::channel();
+        if self
+            .manager
+            .send(TdpManagerCommand::GetTdpLimitRange(tx))
+            .is_err()
+        {
+            return 0;
+        }
+        if let Ok(range) = rx.await {
+            range.map(|r| *r.start()).unwrap_or(0)
+        } else {
+            0
+        }
     }
 
     #[zbus(property(emits_changed_signal = "const"))]
     async fn tdp_limit_max(&self) -> u32 {
-        self.manager
-            .get_tdp_limit_range()
-            .await
-            .map(|r| *r.end())
-            .unwrap_or(0)
+        let (tx, rx) = oneshot::channel();
+        if self
+            .manager
+            .send(TdpManagerCommand::GetTdpLimitRange(tx))
+            .is_err()
+        {
+            return 0;
+        }
+        if let Ok(range) = rx.await {
+            range.map(|r| *r.end()).unwrap_or(0)
+        } else {
+            0
+        }
     }
 }
 
@@ -663,6 +729,7 @@ async fn create_config_interfaces(
     proxy: &Proxy<'static>,
     object_server: &ObjectServer,
     job_manager: &UnboundedSender<JobManagerCommand>,
+    tdp_manager: &UnboundedSender<TdpManagerCommand>,
 ) -> Result<()> {
     let Some(config) = platform_config().await? else {
         return Ok(());
@@ -676,7 +743,7 @@ async fn create_config_interfaces(
     };
     let performance_profile = PerformanceProfile1 {
         proxy: proxy.clone(),
-        tdp_limit_manager: tdp_limit_manager().await.ok(),
+        tdp_limit_manager: tdp_manager.clone(),
     };
     let storage = Storage1 {
         proxy: proxy.clone(),
@@ -700,16 +767,22 @@ async fn create_config_interfaces(
     }
 
     if let Ok(manager) = tdp_limit_manager().await {
+        let low_power_mode = LowPowerMode1 {
+            manager: tdp_manager.clone(),
+        };
+        if config
+            .tdp_limit
+            .as_ref()
+            .and_then(|config| config.download_mode_limit)
+            .is_some()
+        {
+            object_server.at(MANAGER_PATH, low_power_mode).await?;
+        }
         if manager.is_active().await? {
-            object_server
-                .at(
-                    MANAGER_PATH,
-                    TdpLimit1 {
-                        proxy: proxy.clone(),
-                        manager,
-                    },
-                )
-                .await?;
+            let tdp_limit = TdpLimit1 {
+                manager: tdp_manager.clone(),
+            };
+            object_server.at(MANAGER_PATH, tdp_limit).await?;
         }
     }
 
@@ -756,6 +829,7 @@ pub(crate) async fn create_interfaces(
     system: Connection,
     daemon: Sender<Command>,
     job_manager: UnboundedSender<JobManagerCommand>,
+    tdp_manager: UnboundedSender<TdpManagerCommand>,
 ) -> Result<()> {
     let proxy = Builder::<Proxy>::new(&system)
         .destination("com.steampowered.SteamOSManager1")?
@@ -800,7 +874,7 @@ pub(crate) async fn create_interfaces(
     let object_server = session.object_server();
     object_server.at(MANAGER_PATH, manager).await?;
 
-    create_config_interfaces(&proxy, object_server, &job_manager).await?;
+    create_config_interfaces(&proxy, object_server, &job_manager, &tdp_manager).await?;
 
     if device_type().await.unwrap_or_default() == DeviceType::SteamDeck {
         object_server.at(MANAGER_PATH, als).await?;
@@ -867,6 +941,7 @@ mod test {
     use crate::systemd::test::{MockManager, MockUnit};
     use crate::{path, power, testing};
 
+    use std::num::NonZeroU32;
     use std::os::unix::fs::PermissionsExt;
     use std::time::Duration;
     use tokio::fs::{set_permissions, write};
@@ -892,6 +967,7 @@ mod test {
             tdp_limit: Some(TdpLimitConfig {
                 method: TdpLimitingMethod::GpuHwmon,
                 range: Some(RangeConfig::new(3, 15)),
+                download_mode_limit: NonZeroU32::new(6),
             }),
             gpu_clocks: Some(RangeConfig::new(200, 1600)),
             battery_charge_limit: Some(BatteryChargeLimitConfig {
@@ -910,6 +986,7 @@ mod test {
         let mut handle = testing::start();
         let (tx_ctx, _rx_ctx) = channel::<UserContext>();
         let (tx_job, _rx_job) = unbounded_channel::<JobManagerCommand>();
+        let (tx_tdp, _rx_tdp) = unbounded_channel::<TdpManagerCommand>();
 
         if let Some(ref mut config) = platform_config {
             config.set_test_paths();
@@ -945,7 +1022,14 @@ mod test {
             .process_cb
             .set(|_, _| Ok((0, String::from("Interface wlan0"))));
         power::test::create_nodes().await?;
-        create_interfaces(connection.clone(), connection.clone(), tx_ctx, tx_job).await?;
+        create_interfaces(
+            connection.clone(),
+            connection.clone(),
+            tx_ctx,
+            tx_job,
+            tx_tdp,
+        )
+        .await?;
 
         sleep(Duration::from_millis(1)).await;
 
@@ -1083,6 +1167,13 @@ mod test {
             .unwrap());
     }
 
+    #[tokio::test]
+    async fn interface_missing_tdp_limit1() {
+        let test = start(None).await.expect("start");
+
+        assert!(test_interface_missing::<TdpLimit1>(&test.connection).await);
+    }
+
     #[tokio::test]
     async fn interface_matches_hdmi_cec1() {
         let test = start(all_config()).await.expect("start");
@@ -1092,6 +1183,22 @@ mod test {
             .unwrap());
     }
 
+    #[tokio::test]
+    async fn interface_matches_low_power_mode1() {
+        let test = start(all_config()).await.expect("start");
+
+        assert!(test_interface_matches::<LowPowerMode1>(&test.connection)
+            .await
+            .unwrap());
+    }
+
+    #[tokio::test]
+    async fn interface_missing_low_power_mode1() {
+        let test = start(None).await.expect("start");
+
+        assert!(test_interface_missing::<LowPowerMode1>(&test.connection).await);
+    }
+
     #[tokio::test]
     async fn interface_matches_manager2() {
         let test = start(all_config()).await.expect("start");
diff --git a/src/platform.rs b/src/platform.rs
index c96872d..e4c7b54 100644
--- a/src/platform.rs
+++ b/src/platform.rs
@@ -11,6 +11,7 @@ use nix::unistd::{access, AccessFlags};
 use serde::de::Error;
 use serde::{Deserialize, Deserializer};
 use std::io::ErrorKind;
+use std::num::NonZeroU32;
 use std::os::unix::fs::MetadataExt;
 use std::path::PathBuf;
 use strum::VariantNames;
@@ -128,6 +129,7 @@ pub(crate) struct TdpLimitConfig {
     #[serde(deserialize_with = "de_tdp_limiter_method")]
     pub method: TdpLimitingMethod,
     pub range: Option<RangeConfig<u32>>,
+    pub download_mode_limit: Option<NonZeroU32>,
 }
 
 #[derive(Clone, Default, Deserialize, Debug)]
diff --git a/src/power.rs b/src/power.rs
index c8655da..769ee47 100644
--- a/src/power.rs
+++ b/src/power.rs
@@ -10,16 +10,27 @@ use async_trait::async_trait;
 use lazy_static::lazy_static;
 use num_enum::TryFromPrimitive;
 use regex::Regex;
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use std::num::NonZeroU32;
 use std::ops::RangeInclusive;
+use std::os::fd::OwnedFd;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
 use strum::{Display, EnumString, VariantNames};
 use tokio::fs::{self, try_exists, File};
-use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
-use tracing::{error, warn};
+use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader, Interest};
+use tokio::net::unix::pipe;
+use tokio::sync::mpsc::UnboundedReceiver;
+use tokio::sync::oneshot;
+use tokio::task::JoinSet;
+use tracing::{debug, error, warn};
+use zbus::Connection;
 
 use crate::hardware::{device_type, DeviceType};
+use crate::manager::root::RootManagerProxy;
 use crate::platform::platform_config;
+use crate::Service;
 use crate::{path, write_synced};
 
 const HWMON_PREFIX: &str = "/sys/class/hwmon";
@@ -125,6 +136,26 @@ pub(crate) async fn tdp_limit_manager() -> Result<Box<dyn TdpLimitManager>> {
     })
 }
 
+pub(crate) struct TdpManagerService {
+    proxy: RootManagerProxy<'static>,
+    channel: UnboundedReceiver<TdpManagerCommand>,
+    download_set: JoinSet<String>,
+    download_handles: HashMap<String, u32>,
+    download_mode_limit: Option<NonZeroU32>,
+    previous_limit: Option<NonZeroU32>,
+    manager: Box<dyn TdpLimitManager>,
+}
+
+pub(crate) enum TdpManagerCommand {
+    SetTdpLimit(u32),
+    GetTdpLimit(oneshot::Sender<Result<u32>>),
+    GetTdpLimitRange(oneshot::Sender<Result<RangeInclusive<u32>>>),
+    IsActive(oneshot::Sender<Result<bool>>),
+    UpdateDownloadMode,
+    EnterDownloadMode(String, oneshot::Sender<Result<Option<OwnedFd>>>),
+    ListDownloadModeHandles(oneshot::Sender<HashMap<String, u32>>),
+}
+
 async fn read_gpu_sysfs_contents<S: AsRef<Path>>(suffix: S) -> Result<String> {
     // Read a given suffix for the GPU
     let base = find_hwmon(GPU_HWMON_NAME).await?;
@@ -606,15 +637,209 @@ pub(crate) async fn set_platform_profile(name: &str, profile: &str) -> Result<()
         .map_err(|message| anyhow!("Error writing to sysfs: {message}"))
 }
 
+impl TdpManagerService {
+    pub async fn new(
+        channel: UnboundedReceiver<TdpManagerCommand>,
+        connection: &Connection,
+    ) -> Result<TdpManagerService> {
+        let config = platform_config().await?;
+        let config = config
+            .as_ref()
+            .and_then(|config| config.tdp_limit.as_ref())
+            .ok_or(anyhow!("No TDP limit configured"))?;
+
+        let manager = tdp_limit_manager().await?;
+        let proxy = RootManagerProxy::new(connection).await?;
+
+        Ok(TdpManagerService {
+            proxy,
+            channel,
+            download_set: JoinSet::new(),
+            download_handles: HashMap::new(),
+            previous_limit: None,
+            download_mode_limit: config.download_mode_limit,
+            manager,
+        })
+    }
+
+    async fn update_download_mode(&mut self) -> Result<()> {
+        if !self.manager.is_active().await? {
+            return Ok(());
+        }
+
+        let Some(download_mode_limit) = self.download_mode_limit else {
+            return Ok(());
+        };
+
+        let Some(current_limit) = NonZeroU32::new(self.manager.get_tdp_limit().await?) else {
+            // If current_limit is 0 then the interface is broken, likely because TDP limiting
+            // isn't possible with the current power profile or system, so we should just ignore
+            // it for now.
+            return Ok(());
+        };
+
+        if self.download_handles.is_empty() {
+            if let Some(previous_limit) = self.previous_limit {
+                debug!("Leaving download mode, setting TDP to {previous_limit}");
+                self.set_tdp_limit(previous_limit.get()).await?;
+                self.previous_limit = None;
+            }
+        } else {
+            if self.previous_limit.is_none() {
+                debug!("Entering download mode, caching TDP limit of {current_limit}");
+                self.previous_limit = Some(current_limit);
+            }
+            if current_limit != download_mode_limit {
+                self.set_tdp_limit(download_mode_limit.get()).await?;
+            }
+        }
+
+        Ok(())
+    }
+
+    async fn get_download_mode_handle(
+        &mut self,
+        identifier: impl AsRef<str>,
+    ) -> Result<Option<OwnedFd>> {
+        if self.download_mode_limit.is_none() {
+            return Ok(None);
+        }
+        let (send, recv) = pipe::pipe()?;
+        let identifier = identifier.as_ref().to_string();
+        self.download_handles
+            .entry(identifier.clone())
+            .and_modify(|count| *count += 1)
+            .or_insert(1);
+        self.download_set
+            .spawn(TdpManagerService::wait_on_handle(recv, identifier));
+        self.update_download_mode().await?;
+        Ok(Some(send.into_blocking_fd()?))
+    }
+
+    async fn wait_on_handle(recv: pipe::Receiver, identifier: String) -> String {
+        loop {
+            let mut buf = [0; 1024];
+            let read = match recv.ready(Interest::READABLE).await {
+                Ok(r) if r.is_read_closed() => break,
+                Ok(r) if r.is_readable() => recv.try_read(&mut buf),
+                Err(e) => Err(e),
+                Ok(e) => {
+                    warn!("Download mode handle received unexpected event: {e:?}");
+                    break;
+                }
+            };
+            if let Err(e) = read {
+                warn!("Download mode handle received unexpected error: {e:?}");
+                break;
+            }
+        }
+        identifier
+    }
+
+    async fn set_tdp_limit(&self, limit: u32) -> Result<()> {
+        Ok(self
+            .proxy
+            .set_tdp_limit(limit)
+            .await
+            .inspect_err(|e| error!("Failed to set TDP limit: {e}"))?)
+    }
+
+    async fn handle_command(&mut self, command: TdpManagerCommand) -> Result<()> {
+        match command {
+            TdpManagerCommand::SetTdpLimit(limit) => {
+                if self.download_handles.is_empty() {
+                    self.set_tdp_limit(limit).await?;
+                }
+            }
+            TdpManagerCommand::GetTdpLimit(reply) => {
+                let _ = reply.send(self.manager.get_tdp_limit().await);
+            }
+            TdpManagerCommand::GetTdpLimitRange(reply) => {
+                let _ = reply.send(self.manager.get_tdp_limit_range().await);
+            }
+            TdpManagerCommand::IsActive(reply) => {
+                let _ = reply.send(self.manager.is_active().await);
+            }
+            TdpManagerCommand::UpdateDownloadMode => {
+                self.update_download_mode().await?;
+            }
+            TdpManagerCommand::EnterDownloadMode(identifier, reply) => {
+                let fd = self.get_download_mode_handle(identifier).await;
+                let _ = reply.send(fd);
+            }
+            TdpManagerCommand::ListDownloadModeHandles(reply) => {
+                let _ = reply.send(self.download_handles.clone());
+            }
+        }
+        Ok(())
+    }
+}
+
+impl Service for TdpManagerService {
+    const NAME: &'static str = "tdp-manager";
+
+    async fn run(&mut self) -> Result<()> {
+        loop {
+            if self.download_set.is_empty() {
+                let message = match self.channel.recv().await {
+                    None => bail!("TDP manager service channel broke"),
+                    Some(message) => message,
+                };
+                let _ = self
+                    .handle_command(message)
+                    .await
+                    .inspect_err(|e| error!("Failed to handle command: {e}"));
+            } else {
+                tokio::select! {
+                    message = self.channel.recv() => {
+                        let message = match message {
+                            None => bail!("TDP manager service channel broke"),
+                            Some(message) => message,
+                        };
+                        let _ = self.handle_command(message)
+                            .await
+                            .inspect_err(|e| error!("Failed to handle command: {e}"));
+                    },
+                    identifier = self.download_set.join_next() => {
+                        match identifier {
+                            None => (),
+                            Some(Ok(identifier)) => {
+                                match self.download_handles.entry(identifier) {
+                                    Entry::Occupied(e) if e.get() == &1 => {
+                                        e.remove();
+                                        if self.download_handles.is_empty() {
+                                            if let Err(e) = self.update_download_mode().await {
+                                                error!("Failed to update download mode: {e}");
+                                            }
+                                        }
+                                    },
+                                    Entry::Occupied(mut e) => *e.get_mut() -= 1,
+                                    Entry::Vacant(_) => (),
+                                }
+                            }
+                            Some(Err(e)) => warn!("Failed to get closed download mode handle: {e}"),
+                        }
+                    },
+                }
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 pub(crate) mod test {
     use super::*;
+    use crate::error::to_zbus_fdo_error;
     use crate::hardware::test::fake_model;
     use crate::hardware::SteamDeckVariant;
     use crate::platform::{BatteryChargeLimitConfig, PlatformConfig, RangeConfig, TdpLimitConfig};
     use crate::{enum_roundtrip, testing};
     use anyhow::anyhow;
+    use std::time::Duration;
     use tokio::fs::{create_dir_all, read_to_string, remove_dir, write};
+    use tokio::sync::mpsc::{channel, unbounded_channel, Sender};
+    use tokio::time::sleep;
+    use zbus::{fdo, interface};
 
     pub async fn setup() -> Result<()> {
         // Use hwmon5 just as a test. We needed a subfolder of HWMON_PREFIX
@@ -792,6 +1017,7 @@ CCLK_RANGE in Core0:
         platform_config.tdp_limit = Some(TdpLimitConfig {
             method: TdpLimitingMethod::GpuHwmon,
             range: Some(RangeConfig { min: 3, max: 15 }),
+            download_mode_limit: None,
         });
         handle.test.platform_config.replace(Some(platform_config));
         let manager = tdp_limit_manager().await.unwrap();
@@ -815,6 +1041,7 @@ CCLK_RANGE in Core0:
         platform_config.tdp_limit = Some(TdpLimitConfig {
             method: TdpLimitingMethod::GpuHwmon,
             range: Some(RangeConfig { min: 3, max: 15 }),
+            download_mode_limit: None,
         });
         handle.test.platform_config.replace(Some(platform_config));
         let manager = tdp_limit_manager().await.unwrap();
@@ -1360,4 +1587,187 @@ CCLK_RANGE in Core0:
             &["a", "b", "c"]
         );
     }
+
+    struct MockTdpLimit {
+        queue: Sender<()>,
+    }
+
+    #[interface(name = "com.steampowered.SteamOSManager1.RootManager")]
+    impl MockTdpLimit {
+        async fn set_tdp_limit(&mut self, limit: u32) -> fdo::Result<()> {
+            let hwmon = path(HWMON_PREFIX);
+            write(
+                hwmon.join("hwmon5").join(TDP_LIMIT1),
+                format!("{limit}000000\n"),
+            )
+            .await
+            .expect("write");
+            self.queue.send(()).await.map_err(to_zbus_fdo_error)?;
+            Ok(())
+        }
+    }
+
+    #[tokio::test]
+    async fn test_low_power_lock() {
+        let mut h = testing::start();
+        setup().await.expect("setup");
+
+        let connection = h.new_dbus().await.expect("new_dbus");
+        let (tx, rx) = unbounded_channel();
+        let (fin_tx, fin_rx) = oneshot::channel();
+        let (start_tx, start_rx) = oneshot::channel();
+        let (reply_tx, mut reply_rx) = channel(1);
+
+        let iface = MockTdpLimit { queue: reply_tx };
+
+        let mut platform_config = PlatformConfig::default();
+        platform_config.tdp_limit = Some(TdpLimitConfig {
+            method: TdpLimitingMethod::GpuHwmon,
+            range: Some(RangeConfig { min: 3, max: 15 }),
+            download_mode_limit: NonZeroU32::new(6),
+        });
+        h.test.platform_config.replace(Some(platform_config));
+        let manager = tdp_limit_manager().await.unwrap();
+
+        connection
+            .request_name("com.steampowered.SteamOSManager1")
+            .await
+            .expect("reserve_name");
+        let object_server = connection.object_server();
+        object_server
+            .at("/com/steampowered/SteamOSManager1", iface)
+            .await
+            .expect("at");
+
+        let mut service = TdpManagerService::new(rx, &connection)
+            .await
+            .expect("service");
+        let task = tokio::spawn(async move {
+            start_tx.send(()).unwrap();
+            tokio::select! {
+                r = service.run() => r,
+                _ = fin_rx => Ok(()),
+            }
+        });
+        start_rx.await.expect("start_rx");
+
+        sleep(Duration::from_millis(1)).await;
+
+        tx.send(TdpManagerCommand::SetTdpLimit(15)).unwrap();
+        reply_rx.recv().await;
+        assert_eq!(manager.get_tdp_limit().await.unwrap(), 15);
+
+        let (os_tx, os_rx) = oneshot::channel();
+        tx.send(TdpManagerCommand::ListDownloadModeHandles(os_tx))
+            .unwrap();
+        assert!(os_rx.await.unwrap().is_empty());
+
+        let (h_tx, h_rx) = oneshot::channel();
+        tx.send(TdpManagerCommand::EnterDownloadMode(
+            String::from("test"),
+            h_tx,
+        ))
+        .unwrap();
+
+        {
+            let _h = h_rx.await.unwrap().expect("result").expect("handle");
+            reply_rx.recv().await;
+            assert_eq!(manager.get_tdp_limit().await.unwrap(), 6);
+
+            let (os_tx, os_rx) = oneshot::channel();
+            tx.send(TdpManagerCommand::ListDownloadModeHandles(os_tx))
+                .unwrap();
+            assert_eq!(os_rx.await.unwrap(), [(String::from("test"), 1u32)].into());
+
+            tx.send(TdpManagerCommand::SetTdpLimit(15)).unwrap();
+            assert!(tokio::select! {
+                _ = reply_rx.recv() => false,
+                _ = sleep(Duration::from_millis(2)) => true,
+            });
+            assert_eq!(manager.get_tdp_limit().await.unwrap(), 6);
+        }
+        reply_rx.recv().await;
+        assert_eq!(manager.get_tdp_limit().await.unwrap(), 15);
+
+        tx.send(TdpManagerCommand::SetTdpLimit(12)).unwrap();
+        reply_rx.recv().await;
+        assert_eq!(manager.get_tdp_limit().await.unwrap(), 12);
+
+        let (os_tx, os_rx) = oneshot::channel();
+        tx.send(TdpManagerCommand::ListDownloadModeHandles(os_tx))
+            .unwrap();
+        assert!(os_rx.await.unwrap().is_empty());
+
+        fin_tx.send(()).expect("fin");
+        task.await.expect("exit").expect("exit2");
+    }
+
+    #[tokio::test]
+    async fn test_disabled_low_power_lock() {
+        let mut h = testing::start();
+        setup().await.expect("setup");
+
+        let connection = h.new_dbus().await.expect("new_dbus");
+        let (tx, rx) = unbounded_channel();
+        let (fin_tx, fin_rx) = oneshot::channel();
+        let (start_tx, start_rx) = oneshot::channel();
+        let (reply_tx, mut reply_rx) = channel(1);
+
+        let iface = MockTdpLimit { queue: reply_tx };
+
+        let mut platform_config = PlatformConfig::default();
+        platform_config.tdp_limit = Some(TdpLimitConfig {
+            method: TdpLimitingMethod::GpuHwmon,
+            range: Some(RangeConfig { min: 3, max: 15 }),
+            download_mode_limit: None,
+        });
+        h.test.platform_config.replace(Some(platform_config));
+        let manager = tdp_limit_manager().await.unwrap();
+
+        connection
+            .request_name("com.steampowered.SteamOSManager1")
+            .await
+            .expect("reserve_name");
+        let object_server = connection.object_server();
+        object_server
+            .at("/com/steampowered/SteamOSManager1", iface)
+            .await
+            .expect("at");
+
+        let mut service = TdpManagerService::new(rx, &connection)
+            .await
+            .expect("service");
+        let task = tokio::spawn(async move {
+            start_tx.send(()).unwrap();
+            tokio::select! {
+                r = service.run() => r,
+                _ = fin_rx => Ok(()),
+            }
+        });
+        start_rx.await.expect("start_rx");
+
+        sleep(Duration::from_millis(1)).await;
+
+        tx.send(TdpManagerCommand::SetTdpLimit(15)).unwrap();
+        reply_rx.recv().await;
+        assert_eq!(manager.get_tdp_limit().await.unwrap(), 15);
+
+        let (os_tx, os_rx) = oneshot::channel();
+        tx.send(TdpManagerCommand::ListDownloadModeHandles(os_tx))
+            .unwrap();
+        assert!(os_rx.await.unwrap().is_empty());
+
+        let (h_tx, h_rx) = oneshot::channel();
+        tx.send(TdpManagerCommand::EnterDownloadMode(
+            String::from("test"),
+            h_tx,
+        ))
+        .unwrap();
+
+        let h = h_rx.await.unwrap().expect("result");
+        assert!(h.is_none());
+
+        fin_tx.send(()).expect("fin");
+        task.await.expect("exit").expect("exit2");
+    }
 }
diff --git a/src/proxy/low_power_mode1.rs b/src/proxy/low_power_mode1.rs
new file mode 100644
index 0000000..b282a2a
--- /dev/null
+++ b/src/proxy/low_power_mode1.rs
@@ -0,0 +1,27 @@
+//! # D-Bus interface proxy for: `com.steampowered.SteamOSManager1.LowPowerMode1`
+//!
+//! This code was generated by `zbus-xmlgen` `4.1.0` from D-Bus introspection data.
+//! Source: `com.steampowered.SteamOSManager1.xml`.
+//!
+//! You may prefer to adapt it, instead of using it verbatim.
+//!
+//! More information can be found in the [Writing a client proxy] section of the zbus
+//! documentation.
+//!
+//!
+//! [Writing a client proxy]: https://dbus2.github.io/zbus/client.html
+//! [D-Bus standard interfaces]: https://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces,
+use zbus::proxy;
+#[proxy(
+    interface = "com.steampowered.SteamOSManager1.LowPowerMode1",
+    default_service = "com.steampowered.SteamOSManager1",
+    default_path = "/com/steampowered/SteamOSManager1",
+    assume_defaults = true
+)]
+pub trait LowPowerMode1 {
+    /// EnterDownloadMode method
+    fn enter_download_mode(&self, identifier: &str) -> zbus::Result<zbus::zvariant::OwnedFd>;
+
+    /// ListDownloadModeHandles method
+    fn list_download_mode_handles(&self) -> zbus::Result<std::collections::HashMap<String, u32>>;
+}
diff --git a/src/proxy/mod.rs b/src/proxy/mod.rs
index 58d5020..f0e0704 100644
--- a/src/proxy/mod.rs
+++ b/src/proxy/mod.rs
@@ -22,6 +22,7 @@ mod fan_control1;
 mod gpu_performance_level1;
 mod gpu_power_profile1;
 mod hdmi_cec1;
+mod low_power_mode1;
 mod manager2;
 mod performance_profile1;
 mod storage1;
@@ -39,6 +40,7 @@ pub use crate::proxy::fan_control1::FanControl1Proxy;
 pub use crate::proxy::gpu_performance_level1::GpuPerformanceLevel1Proxy;
 pub use crate::proxy::gpu_power_profile1::GpuPowerProfile1Proxy;
 pub use crate::proxy::hdmi_cec1::HdmiCec1Proxy;
+pub use crate::proxy::low_power_mode1::LowPowerMode1Proxy;
 pub use crate::proxy::manager2::Manager2Proxy;
 pub use crate::proxy::performance_profile1::PerformanceProfile1Proxy;
 pub use crate::proxy::storage1::Storage1Proxy;