staging: vchiq: use completions instead of semaphores

It is preferred in the kernel to avoid using semaphores to wait for
events, as they are optimised for the opposite situation; where the
common case is that they are available and may block only occasionally.
FYI see this thread: https://lkml.org/lkml/2008/4/11/323.

Also completions are semantically more explicit in this case.
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c

@@ -44,7 +44,7 @@
 #include <linux/highmem.h>
 #include <linux/pagemap.h>
 #include <linux/bug.h>
-#include <linux/semaphore.h>
+#include <linux/completion.h>
 #include <linux/list.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
@@ -121,9 +121,9 @@ typedef struct user_service_struct {
 	int message_available_pos;
 	int msg_insert;
 	int msg_remove;
-	struct semaphore insert_event;
-	struct semaphore remove_event;
-	struct semaphore close_event;
+	struct completion insert_event;
+	struct completion remove_event;
+	struct completion close_event;
 	VCHIQ_HEADER_T * msg_queue[MSG_QUEUE_SIZE];
 } USER_SERVICE_T;
 
@@ -138,8 +138,8 @@ struct vchiq_instance_struct {
 	VCHIQ_COMPLETION_DATA_T completions[MAX_COMPLETIONS];
 	int completion_insert;
 	int completion_remove;
-	struct semaphore insert_event;
-	struct semaphore remove_event;
+	struct completion insert_event;
+	struct completion remove_event;
 	struct mutex completion_mutex;
 
 	int connected;
@@ -562,7 +562,8 @@ add_completion(VCHIQ_INSTANCE_T instance, VCHIQ_REASON_T reason,
 		vchiq_log_trace(vchiq_arm_log_level,
 			"%s - completion queue full", __func__);
 		DEBUG_COUNT(COMPLETION_QUEUE_FULL_COUNT);
-		if (down_interruptible(&instance->remove_event) != 0) {
+		if (wait_for_completion_interruptible(
+					&instance->remove_event)) {
 			vchiq_log_info(vchiq_arm_log_level,
 				"service_callback interrupted");
 			return VCHIQ_RETRY;
@@ -600,7 +601,7 @@ add_completion(VCHIQ_INSTANCE_T instance, VCHIQ_REASON_T reason,
 	insert++;
 	instance->completion_insert = insert;
 
-	up(&instance->insert_event);
+	complete(&instance->insert_event);
 
 	return VCHIQ_SUCCESS;
 }
@@ -673,7 +674,8 @@ service_callback(VCHIQ_REASON_T reason, VCHIQ_HEADER_T *header,
 			}
 
 			DEBUG_TRACE(SERVICE_CALLBACK_LINE);
-			if (down_interruptible(&user_service->remove_event)
+			if (wait_for_completion_interruptible(
+						&user_service->remove_event)
 				!= 0) {
 				vchiq_log_info(vchiq_arm_log_level,
 					"%s interrupted", __func__);
@@ -705,7 +707,7 @@ service_callback(VCHIQ_REASON_T reason, VCHIQ_HEADER_T *header,
 		}
 
 		spin_unlock(&msg_queue_spinlock);
-		up(&user_service->insert_event);
+		complete(&user_service->insert_event);
 
 		header = NULL;
 	}
@@ -745,7 +747,7 @@ static void close_delivered(USER_SERVICE_T *user_service)
 		unlock_service(user_service->service);
 
 		/* Wake the user-thread blocked in close_ or remove_service */
-		up(&user_service->close_event);
+		complete(&user_service->close_event);
 
 		user_service->close_pending = 0;
 	}
@@ -867,7 +869,7 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		if (status == VCHIQ_SUCCESS) {
 			/* Wake the completion thread and ask it to exit */
 			instance->closing = 1;
-			up(&instance->insert_event);
+			complete(&instance->insert_event);
 		}
 
 		break;
@@ -948,9 +950,9 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 				instance->completion_remove - 1;
 			user_service->msg_insert = 0;
 			user_service->msg_remove = 0;
-			sema_init(&user_service->insert_event, 0);
-			sema_init(&user_service->remove_event, 0);
-			sema_init(&user_service->close_event, 0);
+			init_completion(&user_service->insert_event);
+			init_completion(&user_service->remove_event);
+			init_completion(&user_service->close_event);
 
 			if (args.is_open) {
 				status = vchiq_open_service_internal
@@ -1007,7 +1009,8 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		   has been closed until the client library calls the
 		   CLOSE_DELIVERED ioctl, signalling close_event. */
 		if (user_service->close_pending &&
-			down_interruptible(&user_service->close_event))
+			wait_for_completion_interruptible(
+				&user_service->close_event))
 			status = VCHIQ_RETRY;
 		break;
 	}
@@ -1182,7 +1185,8 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 			DEBUG_TRACE(AWAIT_COMPLETION_LINE);
 			mutex_unlock(&instance->completion_mutex);
-			rc = down_interruptible(&instance->insert_event);
+			rc = wait_for_completion_interruptible(
+						&instance->insert_event);
 			mutex_lock(&instance->completion_mutex);
 			if (rc != 0) {
 				DEBUG_TRACE(AWAIT_COMPLETION_LINE);
@@ -1310,7 +1314,7 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		}
 
 		if (ret != 0)
-			up(&instance->remove_event);
+			complete(&instance->remove_event);
 		mutex_unlock(&instance->completion_mutex);
 		DEBUG_TRACE(AWAIT_COMPLETION_LINE);
 	} break;
@@ -1350,8 +1354,8 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			do {
 				spin_unlock(&msg_queue_spinlock);
 				DEBUG_TRACE(DEQUEUE_MESSAGE_LINE);
-				if (down_interruptible(
-					&user_service->insert_event) != 0) {
+				if (wait_for_completion_interruptible(
+					&user_service->insert_event)) {
 					vchiq_log_info(vchiq_arm_log_level,
 						"DEQUEUE_MESSAGE interrupted");
 					ret = -EINTR;
@@ -1373,7 +1377,7 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		user_service->msg_remove++;
 		spin_unlock(&msg_queue_spinlock);
 
-		up(&user_service->remove_event);
+		complete(&user_service->remove_event);
 		if (header == NULL)
 			ret = -ENOTCONN;
 		else if (header->size <= args.bufsize) {
@@ -1979,8 +1983,8 @@ vchiq_open(struct inode *inode, struct file *file)
 
 		vchiq_debugfs_add_instance(instance);
 
-		sema_init(&instance->insert_event, 0);
-		sema_init(&instance->remove_event, 0);
+		init_completion(&instance->insert_event);
+		init_completion(&instance->remove_event);
 		mutex_init(&instance->completion_mutex);
 		mutex_init(&instance->bulk_waiter_list_mutex);
 		INIT_LIST_HEAD(&instance->bulk_waiter_list);
@@ -2033,12 +2037,12 @@ vchiq_release(struct inode *inode, struct file *file)
 
 		/* Wake the completion thread and ask it to exit */
 		instance->closing = 1;
-		up(&instance->insert_event);
+		complete(&instance->insert_event);
 
 		mutex_unlock(&instance->completion_mutex);
 
 		/* Wake the slot handler if the completion queue is full. */
-		up(&instance->remove_event);
+		complete(&instance->remove_event);
 
 		/* Mark all services for termination... */
 		i = 0;
@@ -2047,7 +2051,7 @@ vchiq_release(struct inode *inode, struct file *file)
 			USER_SERVICE_T *user_service = service->base.userdata;
 
 			/* Wake the slot handler if the msg queue is full. */
-			up(&user_service->remove_event);
+			complete(&user_service->remove_event);
 
 			vchiq_terminate_service_internal(service);
 			unlock_service(service);
@@ -2059,7 +2063,7 @@ vchiq_release(struct inode *inode, struct file *file)
 			!= NULL) {
 			USER_SERVICE_T *user_service = service->base.userdata;
 
-			down(&service->remove_event);
+			wait_for_completion(&service->remove_event);
 
 			BUG_ON(service->srvstate != VCHIQ_SRVSTATE_FREE);
 
@@ -2103,7 +2107,7 @@ vchiq_release(struct inode *inode, struct file *file)
 
 				/* Wake any blocked user-thread */
 				if (instance->use_close_delivered)
-					up(&user_service->close_event);
+					complete(&user_service->close_event);
 				unlock_service(service);
 			}
 			instance->completion_remove++;

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h

@@ -35,7 +35,7 @@
 #define VCHIQ_CORE_H
 
 #include <linux/mutex.h>
-#include <linux/semaphore.h>
+#include <linux/completion.h>
 #include <linux/kthread.h>
 
 #include "vchiq_cfg.h"
@@ -307,8 +307,8 @@ typedef struct vchiq_service_struct {
 	VCHIQ_BULK_QUEUE_T bulk_tx;
 	VCHIQ_BULK_QUEUE_T bulk_rx;
 
-	struct semaphore remove_event;
-	struct semaphore bulk_remove_event;
+	struct completion remove_event;
+	struct completion bulk_remove_event;
 	struct mutex bulk_mutex;
 
 	struct service_stats_struct {
@@ -337,7 +337,7 @@ typedef struct vchiq_service_quota_struct {
 	unsigned short slot_use_count;
 	unsigned short message_quota;
 	unsigned short message_use_count;
-	struct semaphore quota_event;
+	struct completion quota_event;
 	int previous_tx_index;
 } VCHIQ_SERVICE_QUOTA_T;
 
@@ -410,7 +410,7 @@ struct vchiq_state_struct {
 	unsigned short default_message_quota;
 
 	/* Event indicating connect message received */
-	struct semaphore connect;
+	struct completion connect;
 
 	/* Mutex protecting services */
 	struct mutex mutex;
@@ -426,16 +426,16 @@ struct vchiq_state_struct {
 	struct task_struct *sync_thread;
 
 	/* Local implementation of the trigger remote event */
-	struct semaphore trigger_event;
+	struct completion trigger_event;
 
 	/* Local implementation of the recycle remote event */
-	struct semaphore recycle_event;
+	struct completion recycle_event;
 
 	/* Local implementation of the sync trigger remote event */
-	struct semaphore sync_trigger_event;
+	struct completion sync_trigger_event;
 
 	/* Local implementation of the sync release remote event */
-	struct semaphore sync_release_event;
+	struct completion sync_release_event;
 
 	char *tx_data;
 	char *rx_data;
@@ -481,12 +481,12 @@ struct vchiq_state_struct {
 	int unused_service;
 
 	/* Signalled when a free slot becomes available. */
-	struct semaphore slot_available_event;
+	struct completion slot_available_event;
 
-	struct semaphore slot_remove_event;
+	struct completion slot_remove_event;
 
 	/* Signalled when a free data slot becomes available. */
-	struct semaphore data_quota_event;
+	struct completion data_quota_event;
 
 	struct state_stats_struct {
 		int slot_stalls;
@@ -505,7 +505,7 @@ struct vchiq_state_struct {
 
 struct bulk_waiter {
 	VCHIQ_BULK_T *bulk;
-	struct semaphore event;
+	struct completion event;
 	int actual;
 };
 

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_util.c

@@ -48,8 +48,8 @@ int vchiu_queue_init(VCHIU_QUEUE_T *queue, int size)
 	queue->write = 0;
 	queue->initialized = 1;
 
-	sema_init(&queue->pop, 0);
-	sema_init(&queue->push, 0);
+	init_completion(&queue->pop);
+	init_completion(&queue->push);
 
 	queue->storage = kcalloc(size, sizeof(VCHIQ_HEADER_T *), GFP_KERNEL);
 	if (!queue->storage) {
@@ -80,7 +80,7 @@ void vchiu_queue_push(VCHIU_QUEUE_T *queue, VCHIQ_HEADER_T *header)
 		return;
 
 	while (queue->write == queue->read + queue->size) {
-		if (down_interruptible(&queue->pop) != 0)
+		if (wait_for_completion_interruptible(&queue->pop))
 			flush_signals(current);
 	}
 
@@ -100,17 +100,17 @@ void vchiu_queue_push(VCHIU_QUEUE_T *queue, VCHIQ_HEADER_T *header)
 
 	queue->write++;
 
-	up(&queue->push);
+	complete(&queue->push);
 }
 
 VCHIQ_HEADER_T *vchiu_queue_peek(VCHIU_QUEUE_T *queue)
 {
 	while (queue->write == queue->read) {
-		if (down_interruptible(&queue->push) != 0)
+		if (wait_for_completion_interruptible(&queue->push))
 			flush_signals(current);
 	}
 
-	up(&queue->push); // We haven't removed anything from the queue.
+	complete(&queue->push); // We haven't removed anything from the queue.
 
 	/*
 	 * Read from queue->storage must be visible after read from
@@ -126,7 +126,7 @@ VCHIQ_HEADER_T *vchiu_queue_pop(VCHIU_QUEUE_T *queue)
 	VCHIQ_HEADER_T *header;
 
 	while (queue->write == queue->read) {
-		if (down_interruptible(&queue->push) != 0)
+		if (wait_for_completion_interruptible(&queue->push))
 			flush_signals(current);
 	}
 
@@ -146,7 +146,7 @@ VCHIQ_HEADER_T *vchiu_queue_pop(VCHIU_QUEUE_T *queue)
 
 	queue->read++;
 
-	up(&queue->pop);
+	complete(&queue->pop);
 
 	return header;
 }

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_util.h

@@ -35,7 +35,7 @@
 #define VCHIQ_UTIL_H
 
 #include <linux/types.h>
-#include <linux/semaphore.h>
+#include <linux/completion.h>
 #include <linux/mutex.h>
 #include <linux/bitops.h>
 #include <linux/kthread.h>
@@ -60,8 +60,8 @@ typedef struct {
 	int write;
 	int initialized;
 
-	struct semaphore pop;
-	struct semaphore push;
+	struct completion pop;
+	struct completion push;
 
 	VCHIQ_HEADER_T **storage;
 } VCHIU_QUEUE_T;