WIP: ARM/dma-mapping: implement ->alloc_noncontiguous

Implement support for allocating a non-contiguous DMA region. The
implementation is based on the ma-iommu driver.

Signed-off-by: Pavel Golikov <Paullo612@ya.ru>

arch/arm/mm/dma-mapping.c

@@ -1759,6 +1759,63 @@ static void arm_iommu_unmap_sg(struct device *dev,
 	__iommu_unmap_sg(dev, sg, nents, dir, attrs, false);
 }
 
+static struct sg_table *arm_iommu_alloc_noncontiguous(struct device *dev,
+		size_t size, enum dma_data_direction dir, gfp_t gfp,
+		unsigned long attrs)
+{
+	struct dma_sgt_handle *sh;
+	int count;
+
+	sh = kmalloc(sizeof(*sh), gfp);
+	if (!sh)
+		return NULL;
+
+	size = PAGE_ALIGN(size);
+	count = size >> PAGE_SHIFT;
+
+	/*
+	 * Following is a work-around (a.k.a. hack) to prevent pages
+	 * with __GFP_COMP being passed to split_page() which cannot
+	 * handle them.  The real problem is that this flag probably
+	 * should be 0 on ARM as it is not supported on this
+	 * platform; see CONFIG_HUGETLBFS.
+	 */
+	gfp &= ~(__GFP_COMP);
+
+	sh->pages = __iommu_alloc_buffer(dev, size, gfp, attrs, false);
+	if (!sh->pages)
+		goto err_sh;
+
+	if (sg_alloc_table_from_pages(&sh->sgt, sh->pages, count, 0, size,
+	    GFP_KERNEL))
+		goto err_buffer;
+
+	if (__iommu_map_sg(dev, sh->sgt.sgl, sh->sgt.orig_nents, dir, attrs,
+	    false) < 1)
+		goto err_free_sg;
+
+	return &sh->sgt;
+
+err_free_sg:
+	sg_free_table(&sh->sgt);
+err_buffer:
+	__iommu_free_buffer(dev, sh->pages, size, attrs);
+err_sh:
+	kfree(sh);
+	return NULL;
+}
+
+static void arm_iommu_free_noncontiguous(struct device *dev, size_t size,
+			struct sg_table *sgt, enum dma_data_direction dir)
+{
+	struct dma_sgt_handle *sh = sgt_handle(sgt);
+
+	__iommu_unmap_sg(dev, sgt->sgl, sgt->orig_nents, dir, 0, false);
+	__iommu_free_buffer(dev, sh->pages, PAGE_ALIGN(size), 0);
+	sg_free_table(&sh->sgt);
+	kfree(sh);
+}
+
 /**
  * arm_iommu_sync_sg_for_cpu
  * @dev: valid struct device pointer
@@ -1996,6 +2053,8 @@ static const struct dma_map_ops iommu_ops = {
 
 	.map_page		= arm_iommu_map_page,
 	.unmap_page		= arm_iommu_unmap_page,
+	.alloc_noncontiguous    = arm_iommu_alloc_noncontiguous,
+	.free_noncontiguous    = arm_iommu_free_noncontiguous,
 	.sync_single_for_cpu	= arm_iommu_sync_single_for_cpu,
 	.sync_single_for_device	= arm_iommu_sync_single_for_device,