s390/pci_dma: improve map_sg

Our map_sg implementation mapped sg entries independently of each other.
For ease of use and possible performance improvements this patch changes
the implementation to try to map as many (likely physically non-contiguous)
sglist entries as possible into a contiguous DMA segment.
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/pci/pci_dma.c

@@ -388,37 +388,94 @@ static void s390_dma_free(struct device *dev, size_t size,
 	free_pages((unsigned long) pa, get_order(size));
 }
 
-static int s390_dma_map_sg(struct device *dev, struct scatterlist *sg,
-			   int nr_elements, enum dma_data_direction dir,
-			   unsigned long attrs)
+/* Map a segment into a contiguous dma address area */
+static int __s390_dma_map_sg(struct device *dev, struct scatterlist *sg,
+			     size_t size, dma_addr_t *handle,
+			     enum dma_data_direction dir)
 {
-	int mapped_elements = 0;
+	struct zpci_dev *zdev = to_zpci(to_pci_dev(dev));
+	dma_addr_t dma_addr_base, dma_addr;
+	int flags = ZPCI_PTE_VALID;
 	struct scatterlist *s;
-	int i;
+	unsigned long pa;
+	int ret;
 
-	for_each_sg(sg, s, nr_elements, i) {
-		struct page *page = sg_page(s);
-		s->dma_address = s390_dma_map_pages(dev, page, s->offset,
-						    s->length, dir, 0);
-		if (!dma_mapping_error(dev, s->dma_address)) {
-			s->dma_length = s->length;
-			mapped_elements++;
-		} else
+	size = PAGE_ALIGN(size);
+	dma_addr_base = dma_alloc_address(dev, size >> PAGE_SHIFT);
+	if (dma_addr_base == DMA_ERROR_CODE)
+		return -ENOMEM;
+
+	dma_addr = dma_addr_base;
+	if (dir == DMA_NONE || dir == DMA_TO_DEVICE)
+		flags |= ZPCI_TABLE_PROTECTED;
+
+	for (s = sg; dma_addr < dma_addr_base + size; s = sg_next(s)) {
+		pa = page_to_phys(sg_page(s)) + s->offset;
+		ret = dma_update_trans(zdev, pa, dma_addr, s->length, flags);
+		if (ret)
 			goto unmap;
+
+		dma_addr += s->length;
 	}
-out:
-	return mapped_elements;
+	*handle = dma_addr_base;
+	atomic64_add(size >> PAGE_SHIFT, &zdev->mapped_pages);
+
+	return ret;
 
 unmap:
-	for_each_sg(sg, s, mapped_elements, i) {
-		if (s->dma_address)
-			s390_dma_unmap_pages(dev, s->dma_address, s->dma_length,
-					     dir, 0);
-		s->dma_address = 0;
+	dma_update_trans(zdev, 0, dma_addr_base, dma_addr - dma_addr_base,
+			 ZPCI_PTE_INVALID);
+	dma_free_address(dev, dma_addr_base, size >> PAGE_SHIFT);
+	zpci_err("map error:\n");
+	zpci_err_dma(ret, pa);
+	return ret;
+}
+
+static int s390_dma_map_sg(struct device *dev, struct scatterlist *sg,
+			   int nr_elements, enum dma_data_direction dir,
+			   unsigned long attrs)
+{
+	struct scatterlist *s = sg, *start = sg, *dma = sg;
+	unsigned int max = dma_get_max_seg_size(dev);
+	unsigned int size = s->offset + s->length;
+	unsigned int offset = s->offset;
+	int count = 0, i;
+
+	for (i = 1; i < nr_elements; i++) {
+		s = sg_next(s);
+
+		s->dma_address = DMA_ERROR_CODE;
 		s->dma_length = 0;
+
+		if (s->offset || (size & ~PAGE_MASK) ||
+		    size + s->length > max) {
+			if (__s390_dma_map_sg(dev, start, size,
+					      &dma->dma_address, dir))
+				goto unmap;
+
+			dma->dma_address += offset;
+			dma->dma_length = size - offset;
+
+			size = offset = s->offset;
+			start = s;
+			dma = sg_next(dma);
+			count++;
 		}
-	mapped_elements = 0;
-	goto out;
+		size += s->length;
+	}
+	if (__s390_dma_map_sg(dev, start, size, &dma->dma_address, dir))
+		goto unmap;
+
+	dma->dma_address += offset;
+	dma->dma_length = size - offset;
+
+	return count + 1;
+unmap:
+	for_each_sg(sg, s, count, i)
+		s390_dma_unmap_pages(dev, sg_dma_address(s), sg_dma_len(s),
+				     dir, attrs);
+
+	return 0;
 }
 
 static void s390_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
@@ -429,8 +486,9 @@ static void s390_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
 	int i;
 
 	for_each_sg(sg, s, nr_elements, i) {
-		s390_dma_unmap_pages(dev, s->dma_address, s->dma_length, dir,
-				     0);
+		if (s->dma_length)
+			s390_dma_unmap_pages(dev, s->dma_address, s->dma_length,
+					     dir, attrs);
 		s->dma_address = 0;
 		s->dma_length = 0;
 	}