nvme-pci: remove SGL segment descriptors

The max segments this driver can see is 127, well below the 256
threshold needed to add an nvme sgl segment descriptor. Remove all the
useless checks and dead code.
Signed-off-by: NKeith Busch <kbusch@kernel.org>
Reviewed-by: NChaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

drivers/nvme/host/pci.c

@@ -548,22 +548,6 @@ static void nvme_free_prps(struct nvme_dev *dev, struct request *req)
 	}
 }
 
-static void nvme_free_sgls(struct nvme_dev *dev, struct request *req)
-{
-	const int last_sg = SGES_PER_PAGE - 1;
-	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
-	dma_addr_t dma_addr = iod->first_dma;
-	int i;
-
-	for (i = 0; i < iod->nr_allocations; i++) {
-		struct nvme_sgl_desc *sg_list = nvme_pci_iod_list(req)[i];
-		dma_addr_t next_dma_addr = le64_to_cpu((sg_list[last_sg]).addr);
-
-		dma_pool_free(dev->prp_page_pool, sg_list, dma_addr);
-		dma_addr = next_dma_addr;
-	}
-}
-
 static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
 {
 	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
@@ -582,7 +566,8 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
 		dma_pool_free(dev->prp_small_pool, nvme_pci_iod_list(req)[0],
 			      iod->first_dma);
 	else if (iod->use_sgl)
-		nvme_free_sgls(dev, req);
+		dma_pool_free(dev->prp_page_pool, nvme_pci_iod_list(req)[0],
+			      iod->first_dma);
 	else
 		nvme_free_prps(dev, req);
 	mempool_free(iod->sgt.sgl, dev->iod_mempool);
@@ -705,13 +690,8 @@ static void nvme_pci_sgl_set_seg(struct nvme_sgl_desc *sge,
 		dma_addr_t dma_addr, int entries)
 {
 	sge->addr = cpu_to_le64(dma_addr);
-	if (entries < SGES_PER_PAGE) {
-		sge->length = cpu_to_le32(entries * sizeof(*sge));
-		sge->type = NVME_SGL_FMT_LAST_SEG_DESC << 4;
-	} else {
-		sge->length = cpu_to_le32(NVME_CTRL_PAGE_SIZE);
-		sge->type = NVME_SGL_FMT_SEG_DESC << 4;
-	}
+	sge->length = cpu_to_le32(entries * sizeof(*sge));
+	sge->type = NVME_SGL_FMT_LAST_SEG_DESC << 4;
 }
 
 static blk_status_t nvme_pci_setup_sgls(struct nvme_dev *dev,
@@ -751,30 +731,12 @@ static blk_status_t nvme_pci_setup_sgls(struct nvme_dev *dev,
 	iod->first_dma = sgl_dma;
 
 	nvme_pci_sgl_set_seg(&cmd->dptr.sgl, sgl_dma, entries);
-
 	do {
-		if (i == SGES_PER_PAGE) {
-			struct nvme_sgl_desc *old_sg_desc = sg_list;
-			struct nvme_sgl_desc *link = &old_sg_desc[i - 1];
-
-			sg_list = dma_pool_alloc(pool, GFP_ATOMIC, &sgl_dma);
-			if (!sg_list)
-				goto free_sgls;
-
-			i = 0;
-			nvme_pci_iod_list(req)[iod->nr_allocations++] = sg_list;
-			sg_list[i++] = *link;
-			nvme_pci_sgl_set_seg(link, sgl_dma, entries);
-		}
-
 		nvme_pci_sgl_set_data(&sg_list[i++], sg);
 		sg = sg_next(sg);
 	} while (--entries > 0);
 
 	return BLK_STS_OK;
-free_sgls:
-	nvme_free_sgls(dev, req);
-	return BLK_STS_RESOURCE;
 }
 
 static blk_status_t nvme_setup_prp_simple(struct nvme_dev *dev,
@@ -3532,6 +3494,7 @@ static int __init nvme_init(void)
 	BUILD_BUG_ON(IRQ_AFFINITY_MAX_SETS < 2);
 	BUILD_BUG_ON(DIV_ROUND_UP(nvme_pci_npages_prp(), NVME_CTRL_PAGE_SIZE) >
 		     S8_MAX);
+	BUILD_BUG_ON(NVME_MAX_SEGS > SGES_PER_PAGE);
 
 	return pci_register_driver(&nvme_driver);
 }