Subject: [PATCH v4 1/9] dmaengine: Add API to combine configuration and preparation (sg and single)

From: Frank Li <[email-masked]>
Date: Wed, 06 May 2026 16:44:13 -0400

Previously, configuration and preparation required two separate calls. This
works well when configuration is done only once during initialization.

However, in cases where the burst length or source/destination address must
be adjusted for each transfer, calling two functions is verbose and
requires additional locking to ensure both steps complete atomically.

Add a new API dmaengine_prep_config_single() and dmaengine_prep_config_sg()
and callback device_prep_config_sg() that combines configuration and
preparation into a single operation. If the configuration argument is
passed as NULL, fall back to the existing implementation.

Tested-by: Niklas Cassel <[email-masked]>
Signed-off-by: Frank Li <[email-masked]>
---
change in v4
- drop context in device_prep_config_sg()

change in v3
- remove Deprecated for callback device_prep_slave_sg().
- Move condition check before sg init.
- split function at return type.
- move safe version to next patch

change in v2
- add () for function
- use short name device_prep_sg(), remove "slave" and "config". the 'slave'
is reduntant. after remove slave, the function name is difference existed
one, so remove _config suffix.
---
 Documentation/driver-api/dmaengine/client.rst |  9 ++++
 include/linux/dmaengine.h                     | 63 +++++++++++++++++++++++----
 2 files changed, 64 insertions(+), 8 deletions(-)

diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst
index d491e385d61a98b8a804cd823caf254a2dc62cf4..5ee5d4a3596dd986b02f1bce3078ca6c4c1fb45a 100644
--- a/Documentation/driver-api/dmaengine/client.rst
+++ b/Documentation/driver-api/dmaengine/client.rst
@@ -80,6 +80,10 @@ The details of these operations are:
 
   - slave_sg: DMA a list of scatter gather buffers from/to a peripheral
 
+  - config_sg: Similar with slave_sg, just pass down dma_slave_config
+    struct to avoid calling dmaengine_slave_config() every time adjusting the
+    burst length or the FIFO address is needed.
+
   - peripheral_dma_vec: DMA an array of scatter gather buffers from/to a
     peripheral. Similar to slave_sg, but uses an array of dma_vec
     structures instead of a scatterlist.
@@ -106,6 +110,11 @@ The details of these operations are:
 		unsigned int sg_len, enum dma_data_direction direction,
 		unsigned long flags);
 
+     struct dma_async_tx_descriptor *dmaengine_prep_config_sg(
+		struct dma_chan *chan, struct scatterlist *sgl,
+		unsigned int sg_len, enum dma_transfer_direction dir,
+		unsigned long flags, struct dma_slave_config *config);
+
      struct dma_async_tx_descriptor *dmaengine_prep_peripheral_dma_vec(
 		struct dma_chan *chan, const struct dma_vec *vecs,
 		size_t nents, enum dma_data_direction direction,
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index b3d251c9734e95e1b75cf6763d4d2c3a1c6a9910..defa377d2ef54d94e6337cdfa7826a091295535e 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -835,6 +835,7 @@ struct dma_filter {
  *	where the address and size of each segment is located in one entry of
  *	the dma_vec array.
  * @device_prep_slave_sg: prepares a slave dma operation
+ * @device_prep_config_sg: prepares a slave DMA operation with dma_slave_config
  * @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.
@@ -934,6 +935,10 @@ struct dma_device {
 		struct dma_chan *chan, struct scatterlist *sgl,
 		unsigned int sg_len, enum dma_transfer_direction direction,
 		unsigned long flags, void *context);
+	struct dma_async_tx_descriptor *(*device_prep_config_sg)(
+		struct dma_chan *chan, struct scatterlist *sgl,
+		unsigned int sg_len, enum dma_transfer_direction direction,
+		unsigned long flags, struct dma_slave_config *config);
 	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_transfer_direction direction,
@@ -974,22 +979,44 @@ static inline bool is_slave_direction(enum dma_transfer_direction direction)
 	       (direction == DMA_DEV_TO_DEV);
 }
 
-static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_single(
-	struct dma_chan *chan, dma_addr_t buf, size_t len,
-	enum dma_transfer_direction dir, unsigned long flags)
+static inline struct dma_async_tx_descriptor *
+dmaengine_prep_config_single(struct dma_chan *chan, dma_addr_t buf, size_t len,
+			     enum dma_transfer_direction dir,
+			     unsigned long flags,
+			     struct dma_slave_config *config)
 {
 	struct scatterlist sg;
+
+	if (!chan || !chan->device)
+		return NULL;
+
 	sg_init_table(&sg, 1);
 	sg_dma_address(&sg) = buf;
 	sg_dma_len(&sg) = len;
 
-	if (!chan || !chan->device || !chan->device->device_prep_slave_sg)
+	if (chan->device->device_prep_config_sg)
+		return chan->device->device_prep_config_sg(chan, &sg, 1, dir,
+							   flags, config);
+
+	if (config)
+		if (dmaengine_slave_config(chan, config))
+			return NULL;
+
+	if (!chan->device->device_prep_slave_sg)
 		return NULL;
 
 	return chan->device->device_prep_slave_sg(chan, &sg, 1,
 						  dir, flags, NULL);
 }
 
+static inline struct dma_async_tx_descriptor *
+dmaengine_prep_slave_single(struct dma_chan *chan, dma_addr_t buf, size_t len,
+			    enum dma_transfer_direction dir,
+			    unsigned long flags)
+{
+	return dmaengine_prep_config_single(chan, buf, len, dir, flags, NULL);
+}
+
 /**
  * dmaengine_prep_peripheral_dma_vec() - Prepare a DMA scatter-gather descriptor
  * @chan: The channel to be used for this descriptor
@@ -1010,17 +1037,37 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_peripheral_dma_vec(
 							    dir, flags);
 }
 
-static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_sg(
-	struct dma_chan *chan, struct scatterlist *sgl,	unsigned int sg_len,
-	enum dma_transfer_direction dir, unsigned long flags)
+static inline struct dma_async_tx_descriptor *
+dmaengine_prep_config_sg(struct dma_chan *chan, struct scatterlist *sgl,
+			 unsigned int sg_len, enum dma_transfer_direction dir,
+			 unsigned long flags, struct dma_slave_config *config)
 {
-	if (!chan || !chan->device || !chan->device->device_prep_slave_sg)
+	if (!chan || !chan->device)
+		return NULL;
+
+	if (chan->device->device_prep_config_sg)
+		return chan->device->device_prep_config_sg(chan, sgl, sg_len,
+				dir, flags, config);
+
+	if (config)
+		if (dmaengine_slave_config(chan, config))
+			return NULL;
+
+	if (!chan->device->device_prep_slave_sg)
 		return NULL;
 
 	return chan->device->device_prep_slave_sg(chan, sgl, sg_len,
 						  dir, flags, NULL);
 }
 
+static inline struct dma_async_tx_descriptor *
+dmaengine_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
+			unsigned int sg_len, enum dma_transfer_direction dir,
+			unsigned long flags)
+{
+	return dmaengine_prep_config_sg(chan, sgl, sg_len, dir, flags, NULL);
+}
+
 #ifdef CONFIG_RAPIDIO_DMA_ENGINE
 struct rio_dma_ext;
 static inline struct dma_async_tx_descriptor *dmaengine_prep_rio_sg(

-- 
2.43.0