spi: create a message queueing infrastructure

This rips the message queue in the PL022 driver out and pushes
it into (optional) common infrastructure. Drivers that want to
use the message pumping thread will need to define the new
per-messags transfer methods and leave the deprecated transfer()
method as NULL.

Most of the design is described in the documentation changes that
are included in this patch.

Since there is a queue that need to be stopped when the system
is suspending/resuming, two new calls are implemented for the
device drivers to call in their suspend()/resume() functions:
spi_master_suspend() and spi_master_resume().

ChangeLog v1->v2:
- Remove Kconfig entry and do not make the queue support optional
  at all, instead be more agressive and have it as part of the
  compulsory infrastructure.
- If the .transfer() method is implemented, delete print a small
  deprecation notice and do not start the transfer pump.
- Fix a bitrotted comment.
ChangeLog v2->v3:
- Fix up a problematic sequence courtesy of Chris Blair.
- Stop rather than destroy the queue on suspend() courtesy of
  Chris Blair.

Signed-off-by: Chris Blair <chris.blair@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 338 insertions, 1 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index b2ccdea30cb9..5ae1e84d9037 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -30,6 +30,9 @@
 #include <linux/of_spi.h>
 #include <linux/pm_runtime.h>
 #include <linux/export.h>
+#include <linux/sched.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
 
 static void spidev_release(struct device *dev)
 {
@@ -507,6 +510,293 @@ spi_register_board_info(struct spi_board_info const *info, unsigned n)
 
 /*-------------------------------------------------------------------------*/
 
+/**
+ * spi_pump_messages - kthread work function which processes spi message queue
+ * @work: pointer to kthread work struct contained in the master struct
+ *
+ * This function checks if there is any spi message in the queue that
+ * needs processing and if so call out to the driver to initialize hardware
+ * and transfer each message.
+ *
+ */
+static void spi_pump_messages(struct kthread_work *work)
+{
+	struct spi_master *master =
+		container_of(work, struct spi_master, pump_messages);
+	unsigned long flags;
+	bool was_busy = false;
+	int ret;
+
+	/* Lock queue and check for queue work */
+	spin_lock_irqsave(&master->queue_lock, flags);
+	if (list_empty(&master->queue) || !master->running) {
+		if (master->busy) {
+			ret = master->unprepare_transfer_hardware(master);
+			if (ret) {
+				dev_err(&master->dev,
+					"failed to unprepare transfer hardware\n");
+				return;
+			}
+		}
+		master->busy = false;
+		spin_unlock_irqrestore(&master->queue_lock, flags);
+		return;
+	}
+
+	/* Make sure we are not already running a message */
+	if (master->cur_msg) {
+		spin_unlock_irqrestore(&master->queue_lock, flags);
+		return;
+	}
+	/* Extract head of queue */
+	master->cur_msg =
+	    list_entry(master->queue.next, struct spi_message, queue);
+
+	list_del_init(&master->cur_msg->queue);
+	if (master->busy)
+		was_busy = true;
+	else
+		master->busy = true;
+	spin_unlock_irqrestore(&master->queue_lock, flags);
+
+	if (!was_busy) {
+		ret = master->prepare_transfer_hardware(master);
+		if (ret) {
+			dev_err(&master->dev,
+				"failed to prepare transfer hardware\n");
+			return;
+		}
+	}
+
+	ret = master->transfer_one_message(master, master->cur_msg);
+	if (ret) {
+		dev_err(&master->dev,
+			"failed to transfer one message from queue\n");
+		return;
+	}
+}
+
+static int spi_init_queue(struct spi_master *master)
+{
+	struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
+
+	INIT_LIST_HEAD(&master->queue);
+	spin_lock_init(&master->queue_lock);
+
+	master->running = false;
+	master->busy = false;
+
+	init_kthread_worker(&master->kworker);
+	master->kworker_task = kthread_run(kthread_worker_fn,
+					   &master->kworker,
+					   dev_name(&master->dev));
+	if (IS_ERR(master->kworker_task)) {
+		dev_err(&master->dev, "failed to create message pump task\n");
+		return -ENOMEM;
+	}
+	init_kthread_work(&master->pump_messages, spi_pump_messages);
+
+	/*
+	 * Master config will indicate if this controller should run the
+	 * message pump with high (realtime) priority to reduce the transfer
+	 * latency on the bus by minimising the delay between a transfer
+	 * request and the scheduling of the message pump thread. Without this
+	 * setting the message pump thread will remain at default priority.
+	 */
+	if (master->rt) {
+		dev_info(&master->dev,
+			"will run message pump with realtime priority\n");
+		sched_setscheduler(master->kworker_task, SCHED_FIFO, &param);
+	}
+
+	return 0;
+}
+
+/**
+ * spi_get_next_queued_message() - called by driver to check for queued
+ * messages
+ * @master: the master to check for queued messages
+ *
+ * If there are more messages in the queue, the next message is returned from
+ * this call.
+ */
+struct spi_message *spi_get_next_queued_message(struct spi_master *master)
+{
+	struct spi_message *next;
+	unsigned long flags;
+
+	/* get a pointer to the next message, if any */
+	spin_lock_irqsave(&master->queue_lock, flags);
+	if (list_empty(&master->queue))
+		next = NULL;
+	else
+		next = list_entry(master->queue.next,
+				  struct spi_message, queue);
+	spin_unlock_irqrestore(&master->queue_lock, flags);
+
+	return next;
+}
+EXPORT_SYMBOL_GPL(spi_get_next_queued_message);
+
+/**
+ * spi_finalize_current_message() - the current message is complete
+ * @master: the master to return the message to
+ *
+ * Called by the driver to notify the core that the message in the front of the
+ * queue is complete and can be removed from the queue.
+ */
+void spi_finalize_current_message(struct spi_master *master)
+{
+	struct spi_message *mesg;
+	unsigned long flags;
+
+	spin_lock_irqsave(&master->queue_lock, flags);
+	mesg = master->cur_msg;
+	master->cur_msg = NULL;
+
+	queue_kthread_work(&master->kworker, &master->pump_messages);
+	spin_unlock_irqrestore(&master->queue_lock, flags);
+
+	mesg->state = NULL;
+	if (mesg->complete)
+		mesg->complete(mesg->context);
+}
+EXPORT_SYMBOL_GPL(spi_finalize_current_message);
+
+static int spi_start_queue(struct spi_master *master)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&master->queue_lock, flags);
+
+	if (master->running || master->busy) {
+		spin_unlock_irqrestore(&master->queue_lock, flags);
+		return -EBUSY;
+	}
+
+	master->running = true;
+	master->cur_msg = NULL;
+	spin_unlock_irqrestore(&master->queue_lock, flags);
+
+	queue_kthread_work(&master->kworker, &master->pump_messages);
+
+	return 0;
+}
+
+static int spi_stop_queue(struct spi_master *master)
+{
+	unsigned long flags;
+	unsigned limit = 500;
+	int ret = 0;
+
+	spin_lock_irqsave(&master->queue_lock, flags);
+
+	/*
+	 * This is a bit lame, but is optimized for the common execution path.
+	 * A wait_queue on the master->busy could be used, but then the common
+	 * execution path (pump_messages) would be required to call wake_up or
+	 * friends on every SPI message. Do this instead.
+	 */
+	while ((!list_empty(&master->queue) || master->busy) && limit--) {
+		spin_unlock_irqrestore(&master->queue_lock, flags);
+		msleep(10);
+		spin_lock_irqsave(&master->queue_lock, flags);
+	}
+
+	if (!list_empty(&master->queue) || master->busy)
+		ret = -EBUSY;
+	else
+		master->running = false;
+
+	spin_unlock_irqrestore(&master->queue_lock, flags);
+
+	if (ret) {
+		dev_warn(&master->dev,
+			 "could not stop message queue\n");
+		return ret;
+	}
+	return ret;
+}
+
+static int spi_destroy_queue(struct spi_master *master)
+{
+	int ret;
+
+	ret = spi_stop_queue(master);
+
+	/*
+	 * flush_kthread_worker will block until all work is done.
+	 * If the reason that stop_queue timed out is that the work will never
+	 * finish, then it does no good to call flush/stop thread, so
+	 * return anyway.
+	 */
+	if (ret) {
+		dev_err(&master->dev, "problem destroying queue\n");
+		return ret;
+	}
+
+	flush_kthread_worker(&master->kworker);
+	kthread_stop(master->kworker_task);
+
+	return 0;
+}
+
+/**
+ * spi_queued_transfer - transfer function for queued transfers
+ * @spi: spi device which is requesting transfer
+ * @msg: spi message which is to handled is queued to driver queue
+ */
+static int spi_queued_transfer(struct spi_device *spi, struct spi_message *msg)
+{
+	struct spi_master *master = spi->master;
+	unsigned long flags;
+
+	spin_lock_irqsave(&master->queue_lock, flags);
+
+	if (!master->running) {
+		spin_unlock_irqrestore(&master->queue_lock, flags);
+		return -ESHUTDOWN;
+	}
+	msg->actual_length = 0;
+	msg->status = -EINPROGRESS;
+
+	list_add_tail(&msg->queue, &master->queue);
+	if (master->running && !master->busy)
+		queue_kthread_work(&master->kworker, &master->pump_messages);
+
+	spin_unlock_irqrestore(&master->queue_lock, flags);
+	return 0;
+}
+
+static int spi_master_initialize_queue(struct spi_master *master)
+{
+	int ret;
+
+	master->queued = true;
+	master->transfer = spi_queued_transfer;
+
+	/* Initialize and start queue */
+	ret = spi_init_queue(master);
+	if (ret) {
+		dev_err(&master->dev, "problem initializing queue\n");
+		goto err_init_queue;
+	}
+	ret = spi_start_queue(master);
+	if (ret) {
+		dev_err(&master->dev, "problem starting queue\n");
+		goto err_start_queue;
+	}
+
+	return 0;
+
+err_start_queue:
+err_init_queue:
+	spi_destroy_queue(master);
+	return ret;
+}
+
+/*-------------------------------------------------------------------------*/
+
 static void spi_master_release(struct device *dev)
 {
 	struct spi_master *master;
@@ -522,6 +812,7 @@ static struct class spi_master_class = {
 };
 
 
+
 /**
  * spi_alloc_master - allocate SPI master controller
  * @dev: the controller, possibly using the platform_bus
@@ -621,6 +912,17 @@ int spi_register_master(struct spi_master *master)
 	dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev),
 			dynamic ? " (dynamic)" : "");
 
+	/* If we're using a queued driver, start the queue */
+	if (master->transfer)
+		dev_info(dev, "master is unqueued, this is deprecated\n");
+	else {
+		status = spi_master_initialize_queue(master);
+		if (status) {
+			device_unregister(&master->dev);
+			goto done;
+		}
+	}
+
 	mutex_lock(&board_lock);
 	list_add_tail(&master->list, &spi_master_list);
 	list_for_each_entry(bi, &board_list, list)
@@ -636,7 +938,6 @@ done:
 }
 EXPORT_SYMBOL_GPL(spi_register_master);
 
-
 static int __unregister(struct device *dev, void *null)
 {
 	spi_unregister_device(to_spi_device(dev));
@@ -657,6 +958,11 @@ void spi_unregister_master(struct spi_master *master)
 {
 	int dummy;
 
+	if (master->queued) {
+		if (spi_destroy_queue(master))
+			dev_err(&master->dev, "queue remove failed\n");
+	}
+
 	mutex_lock(&board_lock);
 	list_del(&master->list);
 	mutex_unlock(&board_lock);
@@ -666,6 +972,37 @@ void spi_unregister_master(struct spi_master *master)
 }
 EXPORT_SYMBOL_GPL(spi_unregister_master);
 
+int spi_master_suspend(struct spi_master *master)
+{
+	int ret;
+
+	/* Basically no-ops for non-queued masters */
+	if (!master->queued)
+		return 0;
+
+	ret = spi_stop_queue(master);
+	if (ret)
+		dev_err(&master->dev, "queue stop failed\n");
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(spi_master_suspend);
+
+int spi_master_resume(struct spi_master *master)
+{
+	int ret;
+
+	if (!master->queued)
+		return 0;
+
+	ret = spi_start_queue(master);
+	if (ret)
+		dev_err(&master->dev, "queue restart failed\n");
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(spi_master_resume);
+
 static int __spi_master_match(struct device *dev, void *data)
 {
 	struct spi_master *m;