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

Vinod Koul
2025-12-16T12:45:23Z

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

Spell check on subject please :-)

> 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.
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).

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

>
> 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 <Frank.Li@nxp.com>

--
~Vinod