[PATCH 01/15] iio: buffer-dma: Get rid of incoming/outgoing queues

[Paul Cercueil]

The buffer-dma code was using two queues, incoming and outgoing, to
manage the state of the blocks in use.

While this totally works, it adds some complexity to the code,
especially since the code only manages 2 blocks. It is much easier to
just check each block's state manually, and keep a counter for the next
block to dequeue.

Since the new DMABUF based API wouldn't use these incoming and outgoing
queues anyway, getting rid of them now makes the upcoming changes
simpler.

Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
---
 drivers/iio/buffer/industrialio-buffer-dma.c | 68 ++++++++++----------
 include/linux/iio/buffer-dma.h               |  7 +-
 2 files changed, 37 insertions(+), 38 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
index d348af8b9705..abac88f20104 100644
--- a/drivers/iio/buffer/industrialio-buffer-dma.c
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -191,16 +191,8 @@ static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
 
 static void _iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
 {
-	struct iio_dma_buffer_queue *queue = block->queue;
-
-	/*
-	 * The buffer has already been freed by the application, just drop the
-	 * reference.
-	 */
-	if (block->state != IIO_BLOCK_STATE_DEAD) {
+	if (block->state != IIO_BLOCK_STATE_DEAD)
 		block->state = IIO_BLOCK_STATE_DONE;
-		list_add_tail(&block->head, &queue->outgoing);
-	}
 }
 
 /**
@@ -317,11 +309,8 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
 	 * dead. This means we can reset the lists without having to fear
 	 * corrution.
 	 */
-	INIT_LIST_HEAD(&queue->outgoing);
 	spin_unlock_irq(&queue->list_lock);
 
-	INIT_LIST_HEAD(&queue->incoming);
-
 	for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
 		if (queue->fileio.blocks[i]) {
 			block = queue->fileio.blocks[i];
@@ -346,7 +335,6 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
 		}
 
 		block->state = IIO_BLOCK_STATE_QUEUED;
-		list_add_tail(&block->head, &queue->incoming);
 	}
 
 out_unlock:
@@ -401,13 +389,18 @@ int iio_dma_buffer_enable(struct iio_buffer *buffer,
 	struct iio_dev *indio_dev)
 {
 	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
-	struct iio_dma_buffer_block *block, *_block;
+	struct iio_dma_buffer_block *block;
+	unsigned int i;
 
 	mutex_lock(&queue->lock);
 	queue->active = true;
-	list_for_each_entry_safe(block, _block, &queue->incoming, head) {
-		list_del(&block->head);
-		iio_dma_buffer_submit_block(queue, block);
+	queue->fileio.next_dequeue = 0;
+
+	for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
+		block = queue->fileio.blocks[i];
+
+		if (block->state == IIO_BLOCK_STATE_QUEUED)
+			iio_dma_buffer_submit_block(queue, block);
 	}
 	mutex_unlock(&queue->lock);
 
@@ -442,28 +435,33 @@ EXPORT_SYMBOL_GPL(iio_dma_buffer_disable);
 static void iio_dma_buffer_enqueue(struct iio_dma_buffer_queue *queue,
 	struct iio_dma_buffer_block *block)
 {
-	if (block->state == IIO_BLOCK_STATE_DEAD) {
+	if (block->state == IIO_BLOCK_STATE_DEAD)
 		iio_buffer_block_put(block);
-	} else if (queue->active) {
+	else if (queue->active)
 		iio_dma_buffer_submit_block(queue, block);
-	} else {
+	else
 		block->state = IIO_BLOCK_STATE_QUEUED;
-		list_add_tail(&block->head, &queue->incoming);
-	}
 }
 
 static struct iio_dma_buffer_block *iio_dma_buffer_dequeue(
 	struct iio_dma_buffer_queue *queue)
 {
 	struct iio_dma_buffer_block *block;
+	unsigned int idx;
 
 	spin_lock_irq(&queue->list_lock);
-	block = list_first_entry_or_null(&queue->outgoing, struct
-		iio_dma_buffer_block, head);
-	if (block != NULL) {
-		list_del(&block->head);
+
+	idx = queue->fileio.next_dequeue;
+	block = queue->fileio.blocks[idx];
+
+	if (block->state == IIO_BLOCK_STATE_DONE) {
 		block->state = IIO_BLOCK_STATE_DEQUEUED;
+		idx = (idx + 1) % ARRAY_SIZE(queue->fileio.blocks);
+		queue->fileio.next_dequeue = idx;
+	} else {
+		block = NULL;
 	}
+
 	spin_unlock_irq(&queue->list_lock);
 
 	return block;
@@ -539,6 +537,7 @@ size_t iio_dma_buffer_data_available(struct iio_buffer *buf)
 	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buf);
 	struct iio_dma_buffer_block *block;
 	size_t data_available = 0;
+	unsigned int i;
 
 	/*
 	 * For counting the available bytes we'll use the size of the block not
@@ -552,8 +551,15 @@ size_t iio_dma_buffer_data_available(struct iio_buffer *buf)
 		data_available += queue->fileio.active_block->size;
 
 	spin_lock_irq(&queue->list_lock);
-	list_for_each_entry(block, &queue->outgoing, head)
-		data_available += block->size;
+
+	for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
+		block = queue->fileio.blocks[i];
+
+		if (block != queue->fileio.active_block
+		    && block->state == IIO_BLOCK_STATE_DONE)
+			data_available += block->size;
+	}
+
 	spin_unlock_irq(&queue->list_lock);
 	mutex_unlock(&queue->lock);
 
@@ -616,9 +622,6 @@ int iio_dma_buffer_init(struct iio_dma_buffer_queue *queue,
 	queue->dev = dev;
 	queue->ops = ops;
 
-	INIT_LIST_HEAD(&queue->incoming);
-	INIT_LIST_HEAD(&queue->outgoing);
-
 	mutex_init(&queue->lock);
 	spin_lock_init(&queue->list_lock);
 
@@ -645,11 +648,8 @@ void iio_dma_buffer_exit(struct iio_dma_buffer_queue *queue)
 			continue;
 		queue->fileio.blocks[i]->state = IIO_BLOCK_STATE_DEAD;
 	}
-	INIT_LIST_HEAD(&queue->outgoing);
 	spin_unlock_irq(&queue->list_lock);
 
-	INIT_LIST_HEAD(&queue->incoming);
-
 	for (i = 0; i < ARRAY_SIZE(queue->fileio.blocks); i++) {
 		if (!queue->fileio.blocks[i])
 			continue;
diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
index ff15c61bf319..d4ed5ff39d44 100644
--- a/include/linux/iio/buffer-dma.h
+++ b/include/linux/iio/buffer-dma.h
@@ -78,12 +78,15 @@ struct iio_dma_buffer_block {
  * @active_block: Block being used in read()
  * @pos: Read offset in the active block
  * @block_size: Size of each block
+ * @next_dequeue: index of next block that will be dequeued
  */
 struct iio_dma_buffer_queue_fileio {
 	struct iio_dma_buffer_block *blocks[2];
 	struct iio_dma_buffer_block *active_block;
 	size_t pos;
 	size_t block_size;
+
+	unsigned int next_dequeue;
 };
 
 /**
@@ -97,8 +100,6 @@ struct iio_dma_buffer_queue_fileio {
  *   atomic context as well as blocks on those lists. This is the outgoing queue
  *   list and typically also a list of active blocks in the part that handles
  *   the DMA controller
- * @incoming: List of buffers on the incoming queue
- * @outgoing: List of buffers on the outgoing queue
  * @active: Whether the buffer is currently active
  * @fileio: FileIO state
  */
@@ -109,8 +110,6 @@ struct iio_dma_buffer_queue {
 
 	struct mutex lock;
 	spinlock_t list_lock;
-	struct list_head incoming;
-	struct list_head outgoing;
 
 	bool active;
 
-- 
2.33.0