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Subject[PATCHv5] DMAEngine: Define interleaved 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.

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.

Also since now we support SLAVE channels that might not provide
device_prep_slave_sg callback but device_prep_interleaved_dma,
remove the BUG_ON check.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
---
Dan,
After waiting for a reply from you/Alexandre a couple of days I am revising
my patch without adding a hook for RapidIO case for 2 reasons:
a) I think the RapidIO requirement is served better by the concept of
virtual channels, rather than hacking "struct dma_chan" to reach more
than one device.
b) If Alexandre comes up with something irresistible, we can always add
the hook later.

Changes since v4:
1) Dropped the 'frm_irq' member.
2) Renamed 'xfer_direction' to 'dma_transfer_direction'

Changes since v3:
1) Added explicit type for source and destination.

Changes since v2:
1) Added some notes to documentation.
2) Removed the BUG_ON check that expects every SLAVE channel to
provide a prep_slave_sg, as we are now valid otherwise too.
3) Fixed the DMA_TX_TYPE_END offset - made it last element of enum.
4) Renamed prep_dma_genxfer to prep_interleaved_dma as Vinod wanted.

Changes since v1:
1) Dropped the 'dma_transaction_type' member until we really
merge another type into this api. Instead added special
type for this api - DMA_GENXFER in dma_transaction_type.
2) Renamed 'xfer_template' to 'dmaxfer_template' inorder to

Documentation/dmaengine.txt | 8 ++++
drivers/dma/dmaengine.c | 4 +-
include/linux/dmaengine.h | 82 +++++++++++++++++++++++++++++++++++++++++-
3 files changed, 90 insertions(+), 4 deletions(-)
diff --git a/Documentation/dmaengine.txt b/Documentation/dmaengine.txt
index 94b7e0f..962a2d3 100644
--- a/Documentation/dmaengine.txt
+++ b/Documentation/dmaengine.txt
@@ -75,6 +75,10 @@ The slave DMA usage consists of following steps:
slave_sg - DMA a list of scatter gather buffers from/to a peripheral
dma_cyclic - Perform a cyclic DMA operation from/to a peripheral till the
operation is explicitly stopped.
+ interleaved_dma - This is common to Slave as well as M2M clients. For slave
+ address of devices' fifo could be already known to the driver.
+ Various types of operations could be expressed by setting
+ appropriate values to the 'dmaxfer_template' members.

A non-NULL return of this transfer API represents a "descriptor" for
the given transaction.
@@ -89,6 +93,10 @@ The slave DMA usage consists of following steps:
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_interleaved_dma)(
+ struct dma_chan *chan, struct dmaxfer_template *xt,
+ unsigned long flags);
+
The peripheral driver is expected to have mapped the scatterlist for
the DMA operation prior to calling device_prep_slave_sg, and must
keep the scatterlist mapped until the DMA operation has completed.
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index b48967b..a6c6051 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -693,12 +693,12 @@ int dma_async_device_register(struct dma_device *device)
!device->device_prep_dma_interrupt);
BUG_ON(dma_has_cap(DMA_SG, device->cap_mask) &&
!device->device_prep_dma_sg);
- 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);
+ BUG_ON(dma_has_cap(DMA_INTERLEAVE, device->cap_mask) &&
+ !device->device_prep_interleaved_dma);

BUG_ON(!device->device_alloc_chan_resources);
BUG_ON(!device->device_free_chan_resources);
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 8fbf40e..ce8c40a 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -71,11 +71,85 @@ enum dma_transaction_type {
DMA_ASYNC_TX,
DMA_SLAVE,
DMA_CYCLIC,
+ DMA_INTERLEAVE,
+/* last transaction type for creation of the capabilities mask */
+ DMA_TX_TYPE_END,
};

-/* last transaction type for creation of the capabilities mask */
-#define DMA_TX_TYPE_END (DMA_CYCLIC + 1)
+enum dma_transfer_direction {
+ MEM_TO_MEM,
+ MEM_TO_DEV,
+ DEV_TO_MEM,
+ DEV_TO_DEV,
+};
+
+/**
+ * Interleaved 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 dmaxfer_template - Template to convey DMAC the transfer pattern
+ * and attributes.
+ * @src_start: Bus address of source for the first chunk.
+ * @dst_start: Bus address of destination for the first chunk.
+ * @dir: Specifies the type of Source and Destination.
+ * @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.
+ * @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 dmaxfer_template {
+ dma_addr_t src_start;
+ dma_addr_t dst_start;
+ enum dma_transfer_direction dir;
+ bool src_inc;
+ bool dst_inc;
+ bool src_sgl;
+ bool dst_sgl;
+ size_t numf;
+ size_t frame_size;
+ struct data_chunk sgl[0];
+};

/**
* enum dma_ctrl_flags - DMA flags to augment operation preparation,
@@ -432,6 +506,7 @@ 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_interleaved_dma: 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 +571,9 @@ 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_interleaved_dma)(
+ struct dma_chan *chan, struct dmaxfer_template *xt,
+ unsigned long flags);
int (*device_control)(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
unsigned long arg);

--
1.7.4.1


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