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Subject[PATCH] DMAEngine: Define generic transfer request api
Date
Define a new 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 as where the interleave and chunk are only a few bytes,
which call for a very condensed api to convey pattern of the transfer.

This api supports all 4 variants of scatter-gather and contiguous transfer.
Besides, it could also represent common operations like
device_prep_dma_{cyclic, memset, memcpy}
and maybe some more that I am not sure of.
Of course, neither can this api 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@linaro.org>
---
include/linux/dmaengine.h | 73 +++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 73 insertions(+), 0 deletions(-)
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 8fbf40e..74f3ae0 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -76,6 +76,76 @@ 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: Bus address of source for the first chunk.
+ * @dst_start: Bus 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,
@@ -432,6 +502,7 @@ 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_genxfer: Transfer expression in a 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
@@ -496,6 +567,8 @@ 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_genxfer)(
+ struct dma_chan *chan, struct xfer_template *xt);
int (*device_control)(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
unsigned long arg);

--
1.7.4.1


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