Re: [PATCH 6/8] nvmet: pci-epf: Use dmaengine_prep_slave_single_config() API

Bjorn Helgaas
2025-12-10T22:54:56Z

On Mon, Dec 08, 2025 at 12:09:45PM -0500, Frank Li wrote:
> Use the new dmaengine_prep_slave_single_config() API to combine the
> configuration and descriptor preparation into a single call.
>
> Since dmaengine_prep_slave_single_config() performs the configuration
> and preparation atomically, the mutex can be removed.

> @@ -386,22 +386,16 @@ 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_slave_single_config(chan, dma_addr, seg->length,
> + sconf.direction,
> + DMA_CTRL_ACK,
> + &sconf);
> if (!desc) {
> dev_err(dev, "Failed to prepare DMA\n");
> ret = -EIO;
> @@ -423,9 +417,6 @@ 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);
> -

I don't know the dmaengine code, but it's not obvious to me what makes
dmaengine_prep_slave_single_config() itself atomic, since it doesn't
contain any locking.

Bjorn