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

[Bjorn Helgaas <helgaas@kernel.org>]

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