Re: [PATCH 0/8] dmaengine: Add new API to combine onfiguration and descriptor preparation

On Tue, Dec 16, 2025 at 06:15:19PM +0530, Vinod Koul wrote:

On 08-12-25, 12:09, Frank Li wrote:

Spell check on subject please :-)

quoted

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_slave_single(chan, dma_local, len, dir, flags, &sconf);

Nak, we cant change the API like this.

Sorry, it is typo here. in patch
	dmaengine_prep_slave_single_config(chan, dma_local, len, dir, flags, &sconf);

I agree that you can add a new way to call dmaengine_slave_config() and
dmaengine_prep_slave_single() together.
maybe dmaengine_prep_config_perip_single() (yes we can go away with slave, but
cant drop it, as absence means something else entire).

how about dmaengine_prep_peripheral_single() and dmaengine_prep_peripheral_sg()
to align recent added "dmaengine_prep_peripheral_dma_vec()"

I think "peripheral" also is reduntant. dmaengine_prep_single() and
dmaengine_prep_sg() should be enough because
- dmaengine_prep_dma_cyclic() is actually work with prepiperial FIFO
- some prepierial FIFO work like memory, by use shared memory method, like
PCIe map windows.
- argument: config and dir already passdown information to indicate if it
is device preiperial. So needn't indicate at function name.
- maybe later extend to support mem to mem by config becuase adjust burst
size for difference alignment or difference bus fabric port to optimaze
performance.

Frank

I would like to retain the dmaengine_prep_slave_single() as an API for
users to call and invoke. There are users who configure channel once as
well

quoted

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_slave_single_config() API

Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
Frank Li (8):
      dmaengine: Add API to combine configuration and preparation (sg and single)
      PCI: endpoint: pci-epf-test: use new DMA API to simple code
      dmaengine: dw-edma: Use new .device_prep_slave_sg_config() 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_slave_single_config() API
      PCI: epf-mhi:Using new API dmaengine_prep_slave_single_config() to simple code.
      crypto: atmel: Use dmaengine_prep_slave_single_config() API

 drivers/crypto/atmel-aes.c                    | 10 ++---
 drivers/dma/dw-edma/dw-edma-core.c            | 38 +++++++++++-----
 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                     | 64 ++++++++++++++++++++++++---
 6 files changed, 111 insertions(+), 82 deletions(-)
---
base-commit: bc04acf4aeca588496124a6cf54bfce3db327039
change-id: 20251204-dma_prep_config-654170d245a2

Best regards,
--
Frank Li [off-list ref]

--
~Vinod