Hello,

On Wednesday, March 07, 2012 12:22 AM Russell King - ARM Linux wrote:

On Wed, Feb 29, 2012 at 04:04:22PM +0100, Marek Szyprowski wrote:

quoted

+static int arm_iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
+		    void *cpu_addr, dma_addr_t dma_addr, size_t size,
+		    struct dma_attrs *attrs)
+{
+	struct arm_vmregion *c;
+
+	vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot);
+	c = arm_vmregion_find(&consistent_head, (unsigned long)cpu_addr);

What protects this against other insertions/removals from the list?

arm_vmregion_* functions have their own spinlock.

(snipped)

quoted

+	if (c) {
+		struct page **pages = c->priv;
+		__dma_free_remap(cpu_addr, size);
+		__iommu_remove_mapping(dev, handle, size);
+		__iommu_free_buffer(dev, pages, size);
+	}
+}
+
+/*
+ * Map a part of the scatter-gather list into contiguous io address space
+ */
+static int __map_sg_chunk(struct device *dev, struct scatterlist *sg,
+			  size_t size, dma_addr_t *handle,
+			  enum dma_data_direction dir)
+{
+	struct dma_iommu_mapping *mapping = dev->archdata.mapping;
+	dma_addr_t iova, iova_base;
+	int ret = 0;
+	unsigned int count;
+	struct scatterlist *s;
+
+	size = PAGE_ALIGN(size);
+	*handle = ARM_DMA_ERROR;
+
+	iova_base = iova = __alloc_iova(mapping, size);
+	if (iova == ARM_DMA_ERROR)
+		return -ENOMEM;
+
+	for (count = 0, s = sg; count < (size >> PAGE_SHIFT); s = sg_next(s))
+	{
+		phys_addr_t phys = page_to_phys(sg_page(s));
+		unsigned int len = PAGE_ALIGN(s->offset + s->length);
+
+		if (!arch_is_coherent())
+			__dma_page_cpu_to_dev(sg_page(s), s->offset, s->length, dir);
+
+		ret = iommu_map(mapping->domain, iova, phys, len, 0);

Dealing with phys addresses on one part and pages + offset + length
in a different part doesn't look like a good idea.  Why can't there
be some consistency?

Well, I have no idea how to be more consistent here. scatter-lists operates on 
pages + offsets + length parameters. iommu api operates on the whole pages, but
they are referred with physical address. Right now I cannot change any of it, 
at least not it the near future.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center