[PATCH 5/9] nvme-pci: merge the simple PRP and SGL setup into a common helper

[Daniel Gomez]

On 10/06/2025 07.06, Christoph Hellwig wrote:
> nvme_setup_prp_simple and nvme_setup_sgl_simple share a lot of logic.
> Merge them into a single helper that makes use of the previously added
> use_sgl tristate.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  drivers/nvme/host/pci.c | 77 +++++++++++++++++------------------------
>  1 file changed, 32 insertions(+), 45 deletions(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 0b85c11d3c96..50bb1ebe6810 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -814,42 +814,41 @@ static blk_status_t nvme_pci_setup_sgls(struct nvme_queue *nvmeq,
>  	return BLK_STS_OK;
>  }
>  
> -static blk_status_t nvme_setup_prp_simple(struct nvme_dev *dev,
> -		struct request *req, struct nvme_rw_command *cmnd,
> -		struct bio_vec *bv)
> +static blk_status_t nvme_pci_setup_data_simple(struct request *req,
> +		enum nvme_use_sgl use_sgl)
>  {
>  	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> -	unsigned int offset = bv->bv_offset & (NVME_CTRL_PAGE_SIZE - 1);
> -	unsigned int first_prp_len = NVME_CTRL_PAGE_SIZE - offset;
> -
> -	iod->first_dma = dma_map_bvec(dev->dev, bv, rq_dma_dir(req), 0);
> -	if (dma_mapping_error(dev->dev, iod->first_dma))
> +	struct nvme_queue *nvmeq = req->mq_hctx->driver_data;
> +	struct bio_vec bv = req_bvec(req);
> +	unsigned int prp1_offset = bv.bv_offset & (NVME_CTRL_PAGE_SIZE - 1);
> +	bool prp_possible = prp1_offset + bv.bv_len <= NVME_CTRL_PAGE_SIZE * 2;
> +	dma_addr_t dma_addr;
> +
> +	if (!use_sgl && !prp_possible)
> +		return BLK_STS_AGAIN;
> +	if (is_pci_p2pdma_page(bv.bv_page))
> +		return BLK_STS_AGAIN;
> +
> +	dma_addr = dma_map_bvec(nvmeq->dev->dev, &bv, rq_dma_dir(req), 0);
> +	if (dma_mapping_error(nvmeq->dev->dev, dma_addr))
>  		return BLK_STS_RESOURCE;
> -	iod->dma_len = bv->bv_len;
> -
> -	cmnd->dptr.prp1 = cpu_to_le64(iod->first_dma);
> -	if (bv->bv_len > first_prp_len)
> -		cmnd->dptr.prp2 = cpu_to_le64(iod->first_dma + first_prp_len);
> -	else
> -		cmnd->dptr.prp2 = 0;
> -	return BLK_STS_OK;
> -}
> +	iod->dma_len = bv.bv_len;
>  
> -static blk_status_t nvme_setup_sgl_simple(struct nvme_dev *dev,
> -		struct request *req, struct nvme_rw_command *cmnd,
> -		struct bio_vec *bv)
> -{
> -	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> +	if (use_sgl == SGL_FORCED || !prp_possible) {

I couldn't find any place other than this where the new FORCED tristate actually
matters. So instead of passing the use_sgl tristate around, why not just check
here whether SGL is forced?