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

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Message-ID: <aUF2SX/6bV2lHtF0@lizhi-Precision-Tower-5810>
Date: Tue, 16 Dec 2025 10:10:01 -0500
From: Frank Li <Frank.li@....com>
To: Vinod Koul <vkoul@...nel.org>
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 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 :-)
>
> > 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
>
> >
> > 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