[PATCH 3/8] nvme-pci: refactor nvme_pci_use_sgls

[Keith Busch]

On Mon, Jun 23, 2025 at 04:12:25PM +0200, Christoph Hellwig wrote:
> @@ -888,7 +899,9 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
>  		goto out_free_sg;
>  	}
>  
> -	if (nvme_pci_use_sgls(dev, req, iod->sgt.nents))
> +	if (use_sgl == SGL_FORCED ||
> +	    (use_sgl == SGL_SUPPORTED &&
> +	     (!sgl_threshold || nvme_pci_avg_seg_size(req) >= sgl_threshold)))
>  		ret = nvme_pci_setup_sgls(nvmeq, req, &cmnd->rw);

We historically interpreted sgl_threshold set to 0 to mean disable SGL
usage, maybe because the controller is broken or something. It might be
okay to have 0 mean to not consider segment sizes, but I just wanted to
point out this is a different interpretation of the user parameter.