Cyclic transfers are useful for audio where a single buffer divided
in periods has to be transfered endlessly until stopped. After being
prepared the transfer is started using the dma_async_descriptor->tx_submit
function. dma_async_descriptor->callback is called after each period.
The transfer is stopped using the DMA_TERMINATE_ALL callback.
While being used for cyclic transfers the channel cannot be used
for other transfer types.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Haavard Skinnemoen <redacted>
---
 drivers/dma/dmaengine.c   |    2 ++
 include/linux/dmaengine.h |    6 +++++-
 2 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 9d31d5e..e5e79ce 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c

@@ -692,6 +692,8 @@ int dma_async_device_register(struct dma_device *device)
 		!device->device_prep_dma_interrupt);
 	BUG_ON(dma_has_cap(DMA_SLAVE, device->cap_mask) &&
 		!device->device_prep_slave_sg);
+	BUG_ON(dma_has_cap(DMA_CYCLIC, device->cap_mask) &&
+		!device->device_prep_dma_cyclic);
 	BUG_ON(dma_has_cap(DMA_SLAVE, device->cap_mask) &&
 		!device->device_control);
 

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index c61d4ca..0df7864 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h

@@ -67,10 +67,11 @@ enum dma_transaction_type {
 	DMA_PRIVATE,
 	DMA_ASYNC_TX,
 	DMA_SLAVE,
+	DMA_CYCLIC,
 };
 
 /* last transaction type for creation of the capabilities mask */
-#define DMA_TX_TYPE_END (DMA_SLAVE + 1)
+#define DMA_TX_TYPE_END (DMA_CYCLIC + 1)
 
 
 /**

@@ -478,6 +479,9 @@ struct dma_device {
 		struct dma_chan *chan, struct scatterlist *sgl,
 		unsigned int sg_len, enum dma_data_direction direction,
 		unsigned long flags);
+	struct dma_async_tx_descriptor *(*device_prep_dma_cyclic)(
+		struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
+		size_t period_len, enum dma_data_direction direction);
 	int (*device_control)(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
 		unsigned long arg);
 

-- 
1.7.1