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

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Message-ID: <aUFUX0e_h7RGAecz@vaman>
Date: Tue, 16 Dec 2025 18:15:19 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Frank Li <Frank.Li@....com>
Cc: 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>,
	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
Subject: Re: [PATCH 0/8] dmaengine: Add new API to combine onfiguration and
 descriptor preparation

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@....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@....com>

-- 
~Vinod