Subject: [PATCH v4 0/9] dmaengine: Add new API to combine configuration and descriptor preparation

From: Frank Li <[email-masked]>
Date: Wed, 06 May 2026 16:44:12 -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.

	if (dmaengine_slave_config(chan, &sconf)) {
		dev_err(dev, "DMA slave config fail\n");
		return -EIO;
	}

	tx = dmaengine_prep_slave_single(chan, dma_local, len, dir, flags);

After new API added

	tx = dmaengine_prep_config_single(chan, dma_local, len, dir, flags, &sconf);

Additional, prevous two calls requires additional locking to ensure both
steps complete atomically.

    mutex_lock()
    dmaengine_slave_config()
    dmaengine_prep_slave_single()
    mutex_unlock()

after new API added, mutex lock can be moved. See patch
     nvmet: pci-epf: Use dmaengine_prep_config_single_safe() API

Signed-off-by: Frank Li <[email-masked]>
---
Changes in v4:
- remove void* context in config_prep() callback
- use spin lock to protect config() and prep().
- Link to v3: https://lore.kernel.org/r/[email-masked]

Changes in v3:
- collect review tags
- create safe version in framework
- Link to v2: https://lore.kernel.org/r/[email-masked]

Changes in v2:
- Use name dmaengine_prep_config_single() and dmaengine_prep_config_sg()
- Add _safe version to avoid confuse, which needn't additional mutex.
- Update document/
- Update commit message. add () for function name. Use upcase for subject.
- Add more explain for remove lock.
- Link to v1: https://lore.kernel.org/r/[email-masked]

---
Frank Li (9):
      dmaengine: Add API to combine configuration and preparation (sg and single)
      dmaengine: Add safe API to combine configuration and preparation
      PCI: endpoint: pci-epf-test: Use dmaenigne_prep_config_single() to simplify code
      dmaengine: dw-edma: Use new .device_prep_config_sg() callback
      dmaengine: dw-edma: Pass dma_slave_config to dw_edma_device_transfer()
      nvmet: pci-epf: Remove unnecessary dmaengine_terminate_sync() on each DMA transfer
      nvmet: pci-epf: Use dmaengine_prep_config_single_safe() API
      PCI: epf-mhi: Use dmaengine_prep_config_single() to simplify code
      crypto: atmel: Use dmaengine_prep_config_single() API

 Documentation/driver-api/dmaengine/client.rst |   9 ++
 drivers/crypto/atmel-aes.c                    |  10 +--
 drivers/dma/dmaengine.c                       |   2 +
 drivers/dma/dw-edma/dw-edma-core.c            |  41 ++++++---
 drivers/nvme/target/pci-epf.c                 |  21 ++---
 drivers/pci/endpoint/functions/pci-epf-mhi.c  |  52 ++++-------
 drivers/pci/endpoint/functions/pci-epf-test.c |   8 +-
 include/linux/dmaengine.h                     | 121 ++++++++++++++++++++++++--
 8 files changed, 180 insertions(+), 84 deletions(-)
---
base-commit: b9303e6bff706758c167af686b5315ad00233bf8
change-id: 20251204-dma_prep_config-654170d245a2

Best regards,
--
Frank Li <[email-masked]>