Re: [PATCH v2 6/8] nvmet: pci-epf: Use dmaengine_prep_config_single_safe() API
From: Damien Le Moal <dlemoal@kernel.org>
Date: 2025-12-19 10:43:02
Also in:
dmaengine, imx, linux-arm-msm, linux-crypto, linux-nvme, linux-pci, lkml
On 12/19/25 00:56, Frank Li wrote:
Use the new dmaengine_prep_config_single_safe() API to combine the configuration and descriptor preparation into a single call. Since dmaengine_prep_config_single_safe() performs the configuration and preparation atomically and dw edma driver implement prep_config_sg() call back, so dmaengine_prep_config_single() is reentriable, the mutex can be removed.
What about for platforms other than DesignWare EDMA ? This is a generic endpoint driver that can work on any platform that is endpoint capable and that has a DMA channel for the PCI endpoint. The dmaengine_prep_config_single_safe() API should be handling everything transparently for any platform, regardless of the DMA channel driver implementing or not the prep_config_sg() callback. For platforms that do not implement it, I suspect that the mutex will still be needed here. So how to we resolve this ? Ideally, all of that should be hidden by the DMA API. The endpoint driver should not need to deal with these differences.
quoted hunk ↗ jump to hunk
Tested-by: Niklas Cassel <cassel@kernel.org> Signed-off-by: Frank Li <Frank.Li@nxp.com> --- drivers/nvme/target/pci-epf.c | 18 ++++-------------- 1 file changed, 4 insertions(+), 14 deletions(-)diff --git a/drivers/nvme/target/pci-epf.c b/drivers/nvme/target/pci-epf.c index 56b1c6a7706a9e2dd9d8aaf17b440129b948486c..8b5ea5d4c79dfd461b767cfd4033a9e4604c94b1 100644 --- a/drivers/nvme/target/pci-epf.c +++ b/drivers/nvme/target/pci-epf.c@@ -388,22 +388,15 @@ static int nvmet_pci_epf_dma_transfer(struct nvmet_pci_epf *nvme_epf, return -EINVAL; } - mutex_lock(lock); - dma_dev = dmaengine_get_dma_device(chan); dma_addr = dma_map_single(dma_dev, seg->buf, seg->length, dir); ret = dma_mapping_error(dma_dev, dma_addr); if (ret) - goto unlock; - - ret = dmaengine_slave_config(chan, &sconf); - if (ret) { - dev_err(dev, "Failed to configure DMA channel\n"); - goto unmap; - } + return ret; - desc = dmaengine_prep_slave_single(chan, dma_addr, seg->length, - sconf.direction, DMA_CTRL_ACK); + desc = dmaengine_prep_config_single_safe(chan, dma_addr, seg->length, + sconf.direction, + DMA_CTRL_ACK, &sconf); if (!desc) { dev_err(dev, "Failed to prepare DMA\n"); ret = -EIO;@@ -426,9 +419,6 @@ static int nvmet_pci_epf_dma_transfer(struct nvmet_pci_epf *nvme_epf, unmap: dma_unmap_single(dma_dev, dma_addr, seg->length, dir); -unlock: - mutex_unlock(lock); - return ret; }
-- Damien Le Moal Western Digital Research