[RFC] DMAEngine: Define generic transfer request api

[Jassi Brar]

This is an attempt to define an api that could be used for doing
fancy data transfers like interleaved to contiguous copy and vice-versa.
Traditional SG_list based transfers tend to be very inefficient
in such cases. Such cases call for some very condensed api to convey
pattern of the transfer. This is an attempt at that condensed api.

The api supports all 4 variants of scatter-gather and contiguous transfer.
Besides, it could easily represent common operations like
 	device_prep_dma_{cyclic, memset, memcpy}
and maybe some more that I am not sure of.

Of course, this api too can't help transfers that don't lend to DMA by
nature, i.e, scattered tiny read/writes with no periodic pattern. 

Signed-off-by: Jassi Brar <jaswinder.singh at linaro.org>
---
 include/linux/dmaengine.h |   74 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 74 insertions(+), 0 deletions(-)

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index eee7add..a6cdb57 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -74,6 +74,76 @@ enum dma_transaction_type {
 /* last transaction type for creation of the capabilities mask */
 #define DMA_TX_TYPE_END (DMA_CYCLIC + 1)
 
+/**
+ * Generic Transfer Request
+ * ------------------------
+ * A chunk is collection of contiguous bytes to be transfered.
+ * The gap(in bytes) between two chunks is called inter-chunk-gap(ICG).
+ * ICGs may or maynot change between chunks.
+ * A FRAME is the smallest series of contiguous {chunk,icg} pairs,
+ *  that when repeated an integral number of times, specifies the transfer.
+ * A transfer template is specification of a Frame, the number of times
+ *  it is to be repeated and other per-transfer attributes.
+ *
+ * Practically, a client driver would have ready a template for each
+ *  type of transfer it is going to need during its lifetime and
+ *  set only 'src_start' and 'dst_start' before submitting the requests.
+ *
+ *
+ *  |      Frame-1        |       Frame-2       | ~ |       Frame-'numf'  |
+ *  |====....==.===...=...|====....==.===...=...| ~ |====....==.===...=...|
+ *
+ *    ==  Chunk size
+ *    ... ICG
+ */
+
+/**
+ * struct data_chunk - Element of scatter-gather list that makes a frame.
+ * @size: Number of bytes to read from source.
+ *	  size_dst := fn(op, size_src), so doesn't mean much for destination.
+ * @icg: Number of bytes to jump after last src/dst address of this
+ *	 chunk and before first src/dst address for next chunk.
+ *	 Ignored for dst(assumed 0), if dst_inc is true and dst_sgl is false.
+ *	 Ignored for src(assumed 0), if src_inc is true and src_sgl is false.
+ */
+struct data_chunk {
+	size_t size;
+	size_t icg;
+};
+
+/**
+ * struct xfer_template - Template to convey DMAC the transfer pattern
+ *	 and attributes.
+ * @op: The operation to perform on source data before writing it on
+ *	 to destination address.
+ * @src_start: Absolute address of source for the first chunk.
+ * @dst_start: Absolute address of destination for the first chunk.
+ * @src_inc: If the source address increments after reading from it.
+ * @dst_inc: If the destination address increments after writing to it.
+ * @src_sgl: If the 'icg' of sgl[] applies to Source (scattered read).
+ *		Otherwise, source is read contiguously (icg ignored).
+ *		Ignored if src_inc is false.
+ * @dst_sgl: If the 'icg' of sgl[] applies to Destination (scattered write).
+ *		Otherwise, destination is filled contiguously (icg ignored).
+ *		Ignored if dst_inc is false.
+ * @frm_irq: If the client expects DMAC driver to do callback after each frame.
+ * @numf: Number of frames in this template.
+ * @frame_size: Number of chunks in a frame i.e, size of sgl[].
+ * @sgl: Array of {chunk,icg} pairs that make up a frame.
+ */
+struct xfer_template {
+	enum dma_transaction_type op;
+	dma_addr_t src_start;
+	dma_addr_t dst_start;
+	bool src_inc;
+	bool dst_inc;
+	bool src_sgl;
+	bool dst_sgl;
+	bool frm_irq;
+	size_t numf;
+	size_t frame_size;
+	struct data_chunk sgl[0];
+};
 
 /**
  * enum dma_ctrl_flags - DMA flags to augment operation preparation,
@@ -430,6 +500,7 @@ struct dma_tx_state {
  * @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_prep_dma_xfer: Transfer expression in 'most' generic way.
  * @device_control: manipulate all pending operations on a channel, returns
  *	zero or error code
  * @device_tx_status: poll for transaction completion, the optional
@@ -494,6 +565,9 @@ struct dma_device {
 	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);
+	struct dma_async_tx_descriptor *(*device_prep_dma_xfer)(
+		struct dma_chan *chan, struct xfer_template *xt,
+		unsigned long flags);
 	int (*device_control)(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
 		unsigned long arg);
 
-- 
1.7.4.1