text: /* Fallback functions when the main IOMMU code is not compiled in. This
     code is roughly equivalent to i386. */
  #include <linux/mm.h>
  #include <linux/init.h>
  #include <linux/pci.h>
  #include <linux/string.h>
  #include <asm/proto.h>
  #include <asm/processor.h>
  #include <asm/dma.h>
  
  static int
  check_addr(char *name, struct device *hwdev, dma_addr_t bus, size_t size)
  {
          if (hwdev && bus + size > *hwdev->dma_mask) {
  		printk(KERN_ERR
  		    "nommu_%s: overflow %Lx+%lu of device mask %Lx\n",
  	       name, (long long)bus, size, (long long)*hwdev->dma_mask);
  		return 0;
  	}
  	return 1;
  }
  
  static dma_addr_t
  nommu_map_single(struct device *hwdev, void *ptr, size_t size,
  	       int direction)
  {
  	dma_addr_t bus = virt_to_bus(ptr);
  	if (!check_addr("map_single", hwdev, bus, size))
  				return bad_dma_address;
  	return bus;
  }
  
  void nommu_unmap_single(struct device *dev, dma_addr_t addr,size_t size,
  			int direction)
  {
  }
  
  /* Map a set of buffers described by scatterlist in streaming
   * mode for DMA.  This is the scatter-gather version of the
   * above pci_map_single interface.  Here the scatter gather list
   * elements are each tagged with the appropriate dma address
   * and length.  They are obtained via sg_dma_{address,length}(SG).
   *
   * NOTE: An implementation may be able to use a smaller number of
   *       DMA address/length pairs than there are SG table elements.
   *       (for example via virtual mapping capabilities)
   *       The routine returns the number of addr/length pairs actually
   *       used, at most nents.
   *
   * Device ownership issues as mentioned above for pci_map_single are
   * the same here.
   */
  int nommu_map_sg(struct device *hwdev, struct scatterlist *sg,
  	       int nents, int direction)
  {
  	int i;
  
  	BUG_ON(direction == DMA_NONE);
   	for (i = 0; i < nents; i++ ) {
  		struct scatterlist *s = &sg[i];
  		BUG_ON(!s->page);
  		s->dma_address = virt_to_bus(page_address(s->page) +s->offset);
  		if (!check_addr("map_sg", hwdev, s->dma_address, s->length))
  			return 0;
  		s->dma_length = s->length;
  	}
  	return nents;
  }
  
  /* Unmap a set of streaming mode DMA translations.
   * Again, cpu read rules concerning calls here are the same as for
   * pci_unmap_single() above.
   */
  void nommu_unmap_sg(struct device *dev, struct scatterlist *sg,
  		  int nents, int dir)
  {
  }
  
  struct dma_mapping_ops nommu_dma_ops = {
  	.map_single = nommu_map_single,
  	.unmap_single = nommu_unmap_single,
  	.map_sg = nommu_map_sg,
  	.unmap_sg = nommu_unmap_sg,
  	.is_phys = 1,
  };
  
  void __init no_iommu_init(void)
  {
  	if (dma_ops)
  		return;
  	dma_ops = &nommu_dma_ops;
  }
  