[RFC] Add notification support for relay services

embedded-service/src/relay/mod.rs

@@ -164,6 +164,9 @@ pub mod mctp {
         type ResultEnumType: for<'buf> mctp_rs::MctpMessageTrait<'buf, Header = Self::HeaderType>
             + RelayResponse<Self::ServiceIdType, Self::HeaderType>;
 
+        /// Returns a reference to the notification `Listener`.
+        fn notification_listener(&self) -> &crate::relay::notifications::Listener<'_>;
+
         /// Process the provided request and yield a result.
         fn process_request<'a>(
             &'a self,
@@ -449,18 +452,21 @@ pub mod mctp {
 
 
                     pub struct $relay_type_name<'hw> {
+                        listener: $crate::relay::notifications::Listener<'hw>,
                         $(
                             [<$service_name:snake _handler>]: &'hw $service_handler_type,
                         )+
                     }
 
                     impl<'hw> $relay_type_name<'hw> {
                         pub fn new(
+                            listener: $crate::relay::notifications::Listener<'hw>,
                             $(
                                 [<$service_name:snake _handler>]: &'hw $service_handler_type,
                             )+
                         ) -> Self {
                             Self {
+                                listener,
                                 $(
                                     [<$service_name:snake _handler>],
                                 )+
@@ -474,6 +480,10 @@ pub mod mctp {
                         type RequestEnumType = HostRequest;
                         type ResultEnumType = HostResult;
 
+                        fn notification_listener(&self) -> & $crate::relay::notifications::Listener<'_> {
+                            &self.listener
+                        }
+
                         fn process_request<'a>(
                             &'a self,
                             message: HostRequest,
@@ -501,3 +511,129 @@ pub mod mctp {
 
     pub use impl_odp_mctp_relay_handler;
 }
+
+/// Relay service notification support.
+pub mod notifications {
+    use crate::GlobalRawMutex;
+    use core::sync::atomic::{AtomicBool, Ordering};
+    use embassy_sync::channel;
+
+    /// Notification error.
+    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    #[cfg_attr(feature = "defmt", derive(defmt::Format))]
+    pub enum Error {
+        /// A notification is currently being processed.
+        Busy,
+        /// A [`Listener`] has already been instantiated.
+        ListenerInstantiated,
+    }
+
+    /// Notifier.
+    ///
+    /// Used by services to send notifications to the relay service.
+    pub struct Notifier<'ch> {
+        id: u8,
+        sender: channel::Sender<'ch, GlobalRawMutex, u8, 1>,
+    }
+
+    impl<'ch> Notifier<'ch> {
+        /// Notify the relay service that the service holding this [`Notifier`] needs attention from the host.
+        ///
+        /// This will wait if a different notification is currently being processed.
+        pub async fn notify(&self) {
+            self.sender.send(self.id).await
+        }
+
+        /// Try to notify the relay service that the service holding this [`Notifier`] needs attention from the host.
+        ///
+        /// # Errors
+        ///
+        /// Returns [`Error::Busy`] if a different notification is currently being processed.
+        pub fn try_notify(&self) -> Result<(), Error> {
+            self.sender.try_send(self.id).map_err(|_| Error::Busy)
+        }
+    }
+
+    /// Listener.
+    pub struct Listener<'ch> {
+        receiver: channel::Receiver<'ch, GlobalRawMutex, u8, 1>,
+    }
+
+    impl<'ch> Listener<'ch> {
+        /// Wait for a notification from any service, then returns the id associated with that notification.
+        pub async fn listen(&self) -> u8 {
+            self.receiver.receive().await
+        }
+
+        /// Try to listen for a notification from any service.
+        ///
+        /// Returns [`None`] if no notification is currently available.
+        pub fn try_listen(&self) -> Option<u8> {
+            self.receiver.try_receive().ok()
+        }
+    }
+
+    /// Notification handler.
+    pub struct NotificationHandler {
+        // The channel size is fixed to 1 (and not exposed as a configurable generic) so that
+        // it does not need to be exposed to consumers of `Notifier` and `Listener`.
+        //
+        // This is reasonable because notifications are expected to be handled quickly,
+        // and it is unlikely that multiple services will need to notify the host simultaneously.
+        //
+        // In the event that they do, the channel still provides backpressure so no notifications
+        // will be lost and the expected latency is minimal.
+        channel: channel::Channel<GlobalRawMutex, u8, 1>,
+        listener_instantiated: AtomicBool,
+    }
+
+    impl Default for NotificationHandler {
+        fn default() -> Self {
+            Self::new()
+        }
+    }
+
+    impl NotificationHandler {
+        /// Create a new [`NotificationHandler`] instance.
+        ///
+        /// This handler allows as many [`Notifier`]s to be created as needed,
+        /// but only one [`Listener`] may be created.
+        pub fn new() -> Self {
+            Self {
+                channel: channel::Channel::new(),
+                listener_instantiated: AtomicBool::new(false),
+            }
+        }
+
+        /// Create a new [`Notifier`] instance with given id.
+        ///
+        /// This [`Notifier`] is then typically passed to services upon instantiation.
+        ///
+        /// The meaning of the id is platform specific and is opaque to services,
+        /// but expectation is that the relay service understands how to interpret the id.
+        ///
+        /// Thus, the caller should ensure the given id matches what the relay service expects.
+        pub fn new_notifier(&self, id: u8) -> Notifier<'_> {
+            Notifier {
+                id,
+                sender: self.channel.sender(),
+            }
+        }
+
+        /// Create a new [`Listener`] instance.
+        ///
+        /// # Errors
+        ///
+        /// Only one [`Listener`] may exist.
+        /// Attempting to create another will return [`Error::ListenerInstantiated`].
+        pub fn new_listener(&self) -> Result<Listener<'_>, Error> {
+            if !self.listener_instantiated.swap(true, Ordering::Relaxed) {
+                Ok(Listener {
+                    receiver: self.channel.receiver(),
+                })
+            } else {
+                Err(Error::ListenerInstantiated)
+            }
+        }
+    }
+}

espi-service/src/espi_service.rs

@@ -1,6 +1,6 @@
 use core::slice;
 
-use embassy_futures::select::select;
+use embassy_futures::select::select3;
 use embassy_imxrt::espi;
 use embassy_sync::channel::Channel;
 use embassy_sync::mutex::Mutex;
@@ -56,31 +56,32 @@ impl<'hw, RelayHandler: embedded_services::relay::mctp::RelayHandler> Service<'h
     pub(crate) async fn run_service(&self) -> ! {
         let mut espi = self.espi.lock().await;
         loop {
-            let event = select(espi.wait_for_event(), self.host_tx_queue.receive()).await;
+            let event = select3(
+                espi.wait_for_event(),
+                self.host_tx_queue.receive(),
+                self.relay_handler.notification_listener().listen(),
+            )
+            .await;
 
             match event {
-                embassy_futures::select::Either::First(controller_event) => {
+                embassy_futures::select::Either3::First(controller_event) => {
                     self.process_controller_event(&mut espi, controller_event)
                         .await
                         .unwrap_or_else(|e| {
                             error!("Critical error processing eSPI controller event: {:?}", e);
                         });
                 }
-                embassy_futures::select::Either::Second(host_msg) => {
+                embassy_futures::select::Either3::Second(host_msg) => {
                     self.process_response_to_host(&mut espi, host_msg).await
                 }
+                embassy_futures::select::Either3::Third(id) => {
+                    espi.irq_push(id).await;
+                    info!("espi: Notification id {} sent to Host!", id);
+                }
             }
         }
     }
 
-    // TODO The notification system was not actually used, so this is currently dead code.
-    //      We need to implement some interface for triggering notifications from other subsystems, and it may do something like this:
-    //
-    // async fn process_notification_to_host(&self, espi: &mut espi::Espi<'_>, notification: &NotificationMsg) {
-    //     espi.irq_push(notification.offset).await;
-    //     info!("espi: Notification id {} sent to Host!", notification.offset);
-    // }
-
     fn write_to_hw(&self, espi: &mut espi::Espi<'hw>, packet: &[u8]) -> Result<(), embassy_imxrt::espi::Error> {
         // Send packet via your transport medium
         // SAFETY: Safe as the access to espi is protected by a mut reference.

thermal-service/src/lib.rs

@@ -4,6 +4,7 @@
 #![allow(clippy::unwrap_used)]
 
 use embedded_sensors_hal_async::temperature::DegreesCelsius;
+use embedded_services::relay::notifications::Notifier;
 use thermal_service_messages::{ThermalRequest, ThermalResult};
 
 mod context;
@@ -36,21 +37,29 @@ pub enum Event {
 
 pub struct Service<'hw> {
     context: context::Context<'hw>,
+    notifier: Notifier<'hw>,
 }
 
 impl<'hw> Service<'hw> {
     pub async fn init(
         service_storage: &'hw embassy_sync::once_lock::OnceLock<Service<'hw>>,
         sensors: &'hw [&'hw sensor::Device],
         fans: &'hw [&'hw fan::Device],
+        notifier: Notifier<'hw>,
     ) -> &'hw Self {
         service_storage.get_or_init(|| Self {
             context: context::Context::new(sensors, fans),
+            notifier,
         })
     }
 
     /// Send a thermal event
     pub async fn send_event(&self, event: Event) {
+        // If a threshold event is triggered, we want to notify host
+        if matches!(event, Event::ThresholdExceeded(_, _, _) | Event::ThresholdCleared(_, _)) {
+            self.notifier.notify().await;
+        }
+
         self.context.send_event(event).await
     }