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Message-Id: <20251218-dma_prep_config-v2-1-c07079836128@nxp.com>
Date: Thu, 18 Dec 2025 10:56:21 -0500
From: Frank Li <Frank.Li@....com>
To: Vinod Koul <vkoul@...nel.org>, Manivannan Sadhasivam <mani@...nel.org>,
Krzysztof Wilczyński <kwilczynski@...nel.org>,
Kishon Vijay Abraham I <kishon@...nel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>, Christoph Hellwig <hch@....de>,
Sagi Grimberg <sagi@...mberg.me>, Chaitanya Kulkarni <kch@...dia.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>,
Nicolas Ferre <nicolas.ferre@...rochip.com>,
Alexandre Belloni <alexandre.belloni@...tlin.com>,
Claudiu Beznea <claudiu.beznea@...on.dev>, Koichiro Den <den@...inux.co.jp>,
Niklas Cassel <cassel@...nel.org>
Cc: dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org,
mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
linux-crypto@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
imx@...ts.linux.dev, Frank Li <Frank.Li@....com>
Subject: [PATCH v2 1/8] dmaengine: Add API to combine configuration and
preparation (sg and single)
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.
Add a new API dmaengine_prep_config_single_safe() and
dmaengine_prep_config_sg_safe() for re-entrancy, which require driver
implement callback device_prep_config_sg().
Tested-by: Niklas Cassel <cassel@...nel.org>
Signed-off-by: Frank Li <Frank.Li@....com>
---
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 | 103 ++++++++++++++++++++++++--
2 files changed, 105 insertions(+), 7 deletions(-)
diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst
index d491e385d61a98b8a804cd823caf254a2dc62cf4..02c45b7d7a779421411eb9c68325cdedafcfe3b1 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 call dmaengine_slave_config() every time if need
+ adjust burst length or FIFO address.
+
- 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 99efe2b9b4ea9844ca6161208362ef18ef111d96..276dca760f95e1131f5ff5bf69752c4c9cb1bcad 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -835,6 +835,8 @@ 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
+ * (Deprecated, use @device_prep_config_sg)
+ * @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 +936,11 @@ 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,
+ void *context);
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 +981,85 @@ 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)
+/*
+ * Re-entrancy and locking considerations for callers:
+ *
+ * dmaengine_prep_config_single(sg)_safe() is re-entrant and requires the
+ * DMA engine driver to implement device_prep_config_sg(). It returns NULL
+ * if device_prep_config_sg() is not implemented.
+ *
+ * The unsafe variant (without the _safe suffix) falls back to calling
+ * dmaengine_slave_config() and dmaengine_prep_slave_sg() separately.
+ * In this case, additional locking may be required, depending on the
+ * DMA consumer's usage.
+ */
+static inline struct dma_async_tx_descriptor *
+dmaengine_prep_config_sg_safe(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_config_sg)
+ return NULL;
+
+ return chan->device->device_prep_config_sg(chan, sgl, sg_len,
+ dir, flags, config, NULL);
+}
+
+static inline struct dma_async_tx_descriptor *
+dmaengine_prep_config_single_safe(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;
+
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 || !chan->device || !chan->device->device_prep_config_sg)
+ return NULL;
+
+ return chan->device->device_prep_config_sg(chan, &sg, 1, dir,
+ flags, config, NULL);
+}
+
+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;
+
+ sg_init_table(&sg, 1);
+ sg_dma_address(&sg) = buf;
+ sg_dma_len(&sg) = len;
+
+ if (!chan || !chan->device)
+ return NULL;
+
+ if (chan->device->device_prep_config_sg)
+ return dmaengine_prep_config_sg_safe(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
@@ -1009,17 +1079,36 @@ 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(
+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)
+ 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 dmaengine_prep_config_sg_safe(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(
--
2.34.1
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