dmaengine: add possibility for cyclic transfers

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 <haavard.skinnemoen@atmel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

2 files changed, 10 insertions, 1 deletions

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 9d31d5eb95c1..e5e79ced4f4b 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 c61d4ca27bcc..32cd84b47478 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)
 
 
 /**
@@ -422,6 +423,9 @@ struct dma_tx_state {
  * @device_prep_dma_memset: prepares a memset operation
  * @device_prep_dma_interrupt: prepares an end of chain interrupt operation
  * @device_prep_slave_sg: prepares a slave dma operation
+ * @device_prep_dma_cyclic: prepare a cyclic dma operation suitable for audio.
+ *      The function takes a buffer of size buf_len. The callback function will
+ *      be called after period_len bytes have been transferred.
  * @device_control: manipulate all pending operations on a channel, returns
  *      zero or error code
  * @device_tx_status: poll for transaction completion, the optional
@@ -478,6 +482,9 @@ 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);