spi: spi-bfin5xx: Remove deprecated create_singlethread_workqueue

The workqueue "workqueue" serves as a driver message queue.
It has a single work item(&drv_data->pump_messages) and hence doesn't
require ordering. Also, it is not being used on a memory reclaim path.
Hence, the singlethreaded workqueue has been replaced with the use of
system_wq.

System workqueues have been able to handle high level of concurrency
for a long time now and hence it's not required to have a singlethreaded
workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue
created with create_singlethread_workqueue(), system_wq allows multiple
work items to overlap executions even on the same CPU; however, a
per-cpu workqueue doesn't have any CPU locality or global ordering
guarantee unless the target CPU is explicitly specified and thus the
increase of local concurrency shouldn't make any difference.

Work item has been flushed in bfin_spi_destroy_queue() to ensure that there
are no pending tasks while disconnecting the driver.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-bfin5xx.c

@@ -67,8 +67,6 @@ struct bfin_spi_master_data {
 	/* BFIN hookup */
 	struct bfin5xx_spi_master *master_info;
 
-	/* Driver message queue */
-	struct workqueue_struct *workqueue;
 	struct work_struct pump_messages;
 	spinlock_t lock;
 	struct list_head queue;
@@ -359,7 +357,7 @@ static void bfin_spi_giveback(struct bfin_spi_master_data *drv_data)
 	drv_data->cur_msg = NULL;
 	drv_data->cur_transfer = NULL;
 	drv_data->cur_chip = NULL;
-	queue_work(drv_data->workqueue, &drv_data->pump_messages);
+	schedule_work(&drv_data->pump_messages);
 	spin_unlock_irqrestore(&drv_data->lock, flags);
 
 	msg->state = NULL;
@@ -946,7 +944,7 @@ static int bfin_spi_transfer(struct spi_device *spi, struct spi_message *msg)
 	list_add_tail(&msg->queue, &drv_data->queue);
 
 	if (drv_data->running && !drv_data->busy)
-		queue_work(drv_data->workqueue, &drv_data->pump_messages);
+		schedule_work(&drv_data->pump_messages);
 
 	spin_unlock_irqrestore(&drv_data->lock, flags);
 
@@ -1177,12 +1175,7 @@ static int bfin_spi_init_queue(struct bfin_spi_master_data *drv_data)
 	tasklet_init(&drv_data->pump_transfers,
 		     bfin_spi_pump_transfers, (unsigned long)drv_data);
 
-	/* init messages workqueue */
 	INIT_WORK(&drv_data->pump_messages, bfin_spi_pump_messages);
-	drv_data->workqueue = create_singlethread_workqueue(
-				dev_name(drv_data->master->dev.parent));
-	if (drv_data->workqueue == NULL)
-		return -EBUSY;
 
 	return 0;
 }
@@ -1204,7 +1197,7 @@ static int bfin_spi_start_queue(struct bfin_spi_master_data *drv_data)
 	drv_data->cur_chip = NULL;
 	spin_unlock_irqrestore(&drv_data->lock, flags);
 
-	queue_work(drv_data->workqueue, &drv_data->pump_messages);
+	schedule_work(&drv_data->pump_messages);
 
 	return 0;
 }
@@ -1246,7 +1239,7 @@ static int bfin_spi_destroy_queue(struct bfin_spi_master_data *drv_data)
 	if (status != 0)
 		return status;
 
-	destroy_workqueue(drv_data->workqueue);
+	flush_work(&drv_data->pump_messages);
 
 	return 0;
 }