From: Manivannan Sadhasivam <mani@kernel.org>
To: Frank Li <Frank.Li@nxp.com>
Cc: "Vinod Koul" <vkoul@kernel.org>,
"Krzysztof Wilczyński" <kwilczynski@kernel.org>,
"Kishon Vijay Abraham I" <kishon@kernel.org>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Christoph Hellwig" <hch@lst.de>,
"Sagi Grimberg" <sagi@grimberg.me>,
"Chaitanya Kulkarni" <kch@nvidia.com>,
"Herbert Xu" <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
"Nicolas Ferre" <nicolas.ferre@microchip.com>,
"Alexandre Belloni" <alexandre.belloni@bootlin.com>,
"Claudiu Beznea" <claudiu.beznea@tuxon.dev>,
"Koichiro Den" <den@valinux.co.jp>,
"Niklas Cassel" <cassel@kernel.org>,
dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-pci@vger.kernel.org, linux-nvme@lists.infradead.org,
mhi@lists.linux.dev, linux-arm-msm@vger.kernel.org,
linux-crypto@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, imx@lists.linux.dev
Subject: Re: [PATCH v4 2/9] dmaengine: Add safe API to combine configuration and preparation
Date: Tue, 12 May 2026 19:33:15 +0530 [thread overview]
Message-ID: <zaf2zeguq7oyrygv5fdokuo4w3btbcoysi2wmtyzremmdov3xe@reo3hnu7wpgi> (raw)
In-Reply-To: <20260506-dma_prep_config-v4-2-85b3d22babff@nxp.com>
On Wed, May 06, 2026 at 04:44:14PM -0400, Frank Li wrote:
> Introduce dmaengine_prep_config_single_safe() and
> dmaengine_prep_config_sg_safe() to provide a reentrant-safe way to
> combine slave configuration and transfer preparation.
>
> Drivers may implement the new device_prep_config_sg() callback to perform
> both steps atomically. If the callback is not provided, the helpers fall
> back to calling dmaengine_slave_config() followed by
> dmaengine_prep_slave_sg() under per-channel mutex protection.
>
> Tested-by: Niklas Cassel <cassel@kernel.org>
> Signed-off-by: Frank Li <Frank.Li@nxp.com>
> ---
> chagne in v4
> - use spinlock() to protect config() and prep()
>
> change in v3
> - new patch
> ---
> drivers/dma/dmaengine.c | 2 ++
> include/linux/dmaengine.h | 58 +++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 60 insertions(+)
>
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 405bd2fbb4a3b94fd0bf44526f656f6a19feaad0..ba29e60160c1a0148793bb299849bccfebb6d32b 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -1099,6 +1099,8 @@ static int __dma_async_device_channel_register(struct dma_device *device,
> chan->dev->device.parent = device->dev;
> chan->dev->chan = chan;
> chan->dev->dev_id = device->dev_id;
> + spin_lock_init(&chan->lock);
> +
> if (!name)
> dev_set_name(&chan->dev->device, "dma%dchan%d", device->dev_id, chan->chan_id);
> else
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index defa377d2ef54d94e6337cdfa7826a091295535e..23728f3d60804e49cd4cbbd3a513c4936eed5836 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -322,6 +322,8 @@ struct dma_router {
> * @slave: ptr to the device using this channel
> * @cookie: last cookie value returned to client
> * @completed_cookie: last completed cookie for this channel
> + * @lock: protect between config and prepare transfer when driver have not
> + * implemented callback device_prep_config_sg().
> * @chan_id: channel ID for sysfs
> * @dev: class device for sysfs
> * @name: backlink name for sysfs
> @@ -341,6 +343,12 @@ struct dma_chan {
> dma_cookie_t cookie;
> dma_cookie_t completed_cookie;
>
> + /*
> + * protect between config and prepare transfer because *_prep() may be
> + * called from complete callback, which is in GFP_NOSLEEP context.
> + */
> + spinlock_t lock; /* protect between config and prepare transfer since */
Why two comments?
> +
> /* sysfs */
> int chan_id;
> struct dma_chan_dev *dev;
> @@ -1068,6 +1076,56 @@ dmaengine_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
> return dmaengine_prep_config_sg(chan, sgl, sg_len, dir, flags, NULL);
> }
>
> +/*
> + * dmaengine_prep_config_single(sg)_safe() is re-entrant version.
> + *
> + * The unsafe variant (without the _safe suffix) falls back to calling
> + * dmaengine_slave_config() and dmaengine_prep_slave_sg() separately.
> + * In this case, additional locking may be required, depending on the
> + * DMA consumer's usage.
> + *
> + * If dmaengine driver have not implemented call back device_prep_config_sg()
> + * safe version use per-channel spinlock to protect call dmaengine_slave_config()
> + * and dmaengine_prep_slave_sg().
> + */
Use proper kernel-doc comments please...
> +static inline struct dma_async_tx_descriptor *
> +dmaengine_prep_config_sg_safe(struct dma_chan *chan, struct scatterlist *sgl,
> + unsigned int sg_len,
> + enum dma_transfer_direction dir,
> + unsigned long flags,
> + struct dma_slave_config *config)
> +{
> + struct dma_async_tx_descriptor *tx;
> +
> + if (!chan || !chan->device)
> + return NULL;
> +
> + if (!chan->device->device_prep_config_sg)
> + spin_lock(&chan->lock);
> +
> + tx = dmaengine_prep_config_sg(chan, sgl, sg_len, dir, flags, config);
> +
> + if (!chan->device->device_prep_config_sg)
> + spin_unlock(&chan->lock);
> +
> + return tx;
> +}
> +
Missing kernel-doc.
- Mani
--
மணிவண்ணன் சதாசிவம்
next prev parent reply other threads:[~2026-05-12 14:03 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-06 20:44 [PATCH v4 0/9] dmaengine: Add new API to combine configuration and descriptor preparation Frank Li
2026-05-06 20:44 ` [PATCH v4 1/9] dmaengine: Add API to combine configuration and preparation (sg and single) Frank Li
2026-05-06 21:39 ` sashiko-bot
2026-05-12 14:00 ` Manivannan Sadhasivam
2026-05-06 20:44 ` [PATCH v4 2/9] dmaengine: Add safe API to combine configuration and preparation Frank Li
2026-05-06 22:02 ` sashiko-bot
2026-05-12 14:03 ` Manivannan Sadhasivam [this message]
2026-05-06 20:44 ` [PATCH v4 3/9] PCI: endpoint: pci-epf-test: Use dmaenigne_prep_config_single() to simplify code Frank Li
2026-05-06 20:44 ` [PATCH v4 4/9] dmaengine: dw-edma: Use new .device_prep_config_sg() callback Frank Li
2026-05-06 22:17 ` sashiko-bot
2026-05-12 14:03 ` Manivannan Sadhasivam
2026-05-06 20:44 ` [PATCH v4 5/9] dmaengine: dw-edma: Pass dma_slave_config to dw_edma_device_transfer() Frank Li
2026-05-06 22:36 ` sashiko-bot
2026-05-12 14:04 ` Manivannan Sadhasivam
2026-05-06 20:44 ` [PATCH v4 6/9] nvmet: pci-epf: Remove unnecessary dmaengine_terminate_sync() on each DMA transfer Frank Li
2026-05-12 14:05 ` Manivannan Sadhasivam
2026-05-06 20:44 ` [PATCH v4 7/9] nvmet: pci-epf: Use dmaengine_prep_config_single_safe() API Frank Li
2026-05-06 23:05 ` sashiko-bot
2026-05-12 14:06 ` Manivannan Sadhasivam
2026-05-06 20:44 ` [PATCH v4 8/9] PCI: epf-mhi: Use dmaengine_prep_config_single() to simplify code Frank Li
2026-05-06 23:26 ` sashiko-bot
2026-05-06 20:44 ` [PATCH v4 9/9] crypto: atmel: Use dmaengine_prep_config_single() API Frank Li
2026-05-06 23:31 ` sashiko-bot
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