Re: [Linaro-mm-sig] [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper

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

+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?

• if (c) {

• struct page **pages = c->priv;
  

• unsigned long uaddr = vma->vm_start;
  

• unsigned long usize = vma->vm_end - vma->vm_start;
  

• int i = 0;
  

• do {
  

• 	int ret;
  

• 	ret = vm_insert_page(vma, uaddr, pages[i++]);
  

• 	if (ret) {
  

• 		pr_err("Remapping memory, error: %d\n", ret);
  

• 		return ret;
  

• 	}
  

• 	uaddr += PAGE_SIZE;
  

• 	usize -= PAGE_SIZE;
  

• } while (usize > 0);
  

• }
• return 0;

+}

+/*

• • free a page as defined by the above mapping.
• • Must not be called with IRQs disabled.
• */

+void arm_iommu_free_attrs(struct device *dev, size_t size, void *cpu_addr,

• 	  dma_addr_t handle, struct dma_attrs *attrs)
  

+{

• struct arm_vmregion *c;
• size = PAGE_ALIGN(size);
• c = arm_vmregion_find(&consistent_head, (unsigned long)cpu_addr);

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

• 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?