[RFC PATCH 5/5] iio: buffer-dma: add support for cyclic DMA transfers

[Alexandru Ardelean <alexandru.ardelean@analog.com>]

From: Lars-Peter Clausen <lars@metafoo.de>

This change adds support for cyclic DMA transfers using the IIO buffer DMA
infrastructure.
To do this, userspace must set the IIO_BUFFER_BLOCK_FLAG_CYCLIC flag on the
block when enqueueing them via the ENQUEUE_BLOCK ioctl().

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
 .../buffer/industrialio-buffer-dmaengine.c    | 24 ++++++++++++-------
 include/uapi/linux/iio/buffer.h               |  1 +
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
index 013cc7c1ecf4..94c93a636ad4 100644
--- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
+++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
@@ -82,14 +82,22 @@ static int iio_dmaengine_buffer_submit_block(struct iio_dma_buffer_queue *queue,
 
 	direction = dmaengine_buffer->is_tx ? DMA_MEM_TO_DEV : DMA_DEV_TO_MEM;
 
-	desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
-		block->phys_addr, block->block.bytes_used, direction,
-		DMA_PREP_INTERRUPT);
-	if (!desc)
-		return -ENOMEM;
-
-	desc->callback_result = iio_dmaengine_buffer_block_done;
-	desc->callback_param = block;
+	if (block->block.flags & IIO_BUFFER_BLOCK_FLAG_CYCLIC) {
+		desc = dmaengine_prep_dma_cyclic(dmaengine_buffer->chan,
+			block->phys_addr, block->block.bytes_used,
+			block->block.bytes_used, direction, 0);
+		if (!desc)
+			return -ENOMEM;
+	} else {
+		desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
+			block->phys_addr, block->block.bytes_used, direction,
+			DMA_PREP_INTERRUPT);
+		if (!desc)
+			return -ENOMEM;
+
+		desc->callback_result = iio_dmaengine_buffer_block_done;
+		desc->callback_param = block;
+	}
 
 	cookie = dmaengine_submit(desc);
 	if (dma_submit_error(cookie))
diff --git a/include/uapi/linux/iio/buffer.h b/include/uapi/linux/iio/buffer.h
index 70ad3aea01ea..0e0c95f1c38b 100644
--- a/include/uapi/linux/iio/buffer.h
+++ b/include/uapi/linux/iio/buffer.h
@@ -13,6 +13,7 @@ struct iio_buffer_block_alloc_req {
 };
 
 #define IIO_BUFFER_BLOCK_FLAG_TIMESTAMP_VALID	(1 << 0)
+#define IIO_BUFFER_BLOCK_FLAG_CYCLIC		(1 << 1)
 
 struct iio_buffer_block {
 	__u32 id;
-- 
2.17.1