Re: [PATCH v3 0/9] dmaengine: Add new API to combine configuration and descriptor preparation

On Mon, Jan 05, 2026 at 05:46:50PM -0500, Frank Li wrote:
> 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 protected]>
> ---

Vinod:
	Can you take care these patches? At least first 2 patches! So
I can did more clean up at next kernel release.

Frank

> Changes in v3:
> - collect review tags
> - create safe version in framework
> - Link to v2: https://lore.kernel.org/r/[email protected]
>
> 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 protected]
>
> ---
> 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                       |   3 +
>  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                     | 117 ++++++++++++++++++++++++--
>  8 files changed, 177 insertions(+), 84 deletions(-)
> ---
> base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
> change-id: 20251204-dma_prep_config-654170d245a2
>
> Best regards,
> --
> Frank Li <[email protected]>
>