Reduce expansion control thread stack size, add comments

applications/services/expansion/expansion_worker.h

@@ -1,20 +1,78 @@
+/**
+ * @file expansion_worker.h
+ * @brief Expansion module handling thread wrapper.
+ *
+ * The worker is started each time an expansion module is detected
+ * and handles all of the communication protocols. Likewise, it is stopped
+ * upon module disconnection or communication error.
+ *
+ * @warning This file is a private implementation detail. Please do not attempt to use it in applications.
+ */
 #pragma once
 
 #include <furi_hal_serial_types.h>
 
+/**
+ * @brief Expansion worker opaque type declaration.
+ */
 typedef struct ExpansionWorker ExpansionWorker;
 
-typedef void (*ExpansionWorkerCallback)(void*);
+/**
+ * @brief Worker callback type.
+ *
+ * @see expansion_worker_set_callback()
+ *
+ * @param[in,out] context pointer to a user-defined object.
+ */
+typedef void (*ExpansionWorkerCallback)(void* context);
 
+/**
+ * @brief Create an expansion worker instance.
+ *
+ * @param[in] serial_id numerical identifier of the serial to be used by the worker.
+ * @returns pointer to the created instance.
+ */
 ExpansionWorker* expansion_worker_alloc(FuriHalSerialId serial_id);
 
+/**
+ * @brief Delete an expansion worker instance.
+ *
+ * @param[in,out] instance pointer to the instance to be deleted.
+ */
 void expansion_worker_free(ExpansionWorker* instance);
 
+/**
+ * @brief Set the module disconnect callback.
+ *
+ * The callback will be triggered upon worker stop EXCEPT
+ * when it was stopped via an expansion_worker_stop() call.
+ *
+ * In other words, the callback will ONLY be triggered if the worker was
+ * stopped due to the user disconnecting/resetting/powering down the module,
+ * or due to some communication error.
+ *
+ * @param[in,out] instance pointer to the worker instance to be modified.
+ * @param[in] callback pointer to the callback function to be called under the above conditions.
+ * @param[in] context pointer to a user-defined object, will be passed as a parameter to the callback.
+ */
 void expansion_worker_set_callback(
     ExpansionWorker* instance,
     ExpansionWorkerCallback callback,
     void* context);
 
+/**
+ * @brief Start the expansion module worker.
+ *
+ * @param[in,out] instance pointer to the worker instance to be started.
+ */
 void expansion_worker_start(ExpansionWorker* instance);
 
+/**
+ * @brief Stop the expansion module worker.
+ *
+ * If the worker was stopped via this call (and not because of module disconnect/
+ * protocol error), the callback will not be triggered.
+ *
+ * @param[in,out] instance pointer to the worker instance to be stopped.
+ */
 void expansion_worker_stop(ExpansionWorker* instance);