dmaengine: add DMA_PREP_CMD for non-Data descriptors.

Some of the DMA controllers are capable of issuing the commands
to peripheral by the DMA. These commands can be list of register
reads/writes and its different from normal data reads/writes.
This patch adds new flag DMA_PREP_CMD in DMA API which tells
the driver that the data passed to DMA API is command data
and DMA controller driver will form descriptor in the required
format.

This flag can be used by any DMA controller driver which requires
the descriptor in different format for non-Data descriptors.
Signed-off-by: NAbhishek Sahu <absahu@codeaurora.org>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>

Documentation/dmaengine/provider.txt

@@ -395,6 +395,13 @@ where to put them)
 	  when DMA_CTRL_REUSE is already set
 	- Terminating the channel
 
+  * DMA_PREP_CMD
+    - If set, the client driver tells DMA controller that passed data in DMA
+      API is command data.
+    - Interpretation of command data is DMA controller specific. It can be
+      used for issuing commands to other peripherals/register reads/register
+      writes for which the descriptor should be in different format from
+      normal data descriptors.
 
 General Design Notes
 --------------------

include/linux/dmaengine.h

@@ -186,6 +186,9 @@ struct dma_interleaved_template {
  *  on the result of this operation
  * @DMA_CTRL_REUSE: client can reuse the descriptor and submit again till
  *  cleared or freed
+ * @DMA_PREP_CMD: tell the driver that the data passed to DMA API is command
+ *  data and the descriptor should be in different format from normal
+ *  data descriptors.
  */
 enum dma_ctrl_flags {
 	DMA_PREP_INTERRUPT = (1 << 0),
@@ -195,6 +198,7 @@ enum dma_ctrl_flags {
 	DMA_PREP_CONTINUE = (1 << 4),
 	DMA_PREP_FENCE = (1 << 5),
 	DMA_CTRL_REUSE = (1 << 6),
+	DMA_PREP_CMD = (1 << 7),
 };
 
 /**