/**
   * iommu_fill_pdir - Insert coalesced scatter/gather chunks into the I/O Pdir.
   * @ioc: The I/O Controller.
   * @startsg: The scatter/gather list of coalesced chunks.
   * @nents: The number of entries in the scatter/gather list.
   * @hint: The DMA Hint.
   *
   * This function inserts the coalesced scatter/gather list chunks into the
   * I/O Controller's I/O Pdir.
   */ 
  static inline unsigned int
  iommu_fill_pdir(struct ioc *ioc, struct scatterlist *startsg, int nents, 
  		unsigned long hint,
  		void (*iommu_io_pdir_entry)(u64 *, space_t, unsigned long,
  					    unsigned long))
  {
  	struct scatterlist *dma_sg = startsg;	/* pointer to current DMA */
  	unsigned int n_mappings = 0;
  	unsigned long dma_offset = 0, dma_len = 0;
  	u64 *pdirp = NULL;
  
  	/* Horrible hack.  For efficiency's sake, dma_sg starts one 
  	 * entry below the true start (it is immediately incremented
  	 * in the loop) */
  	 dma_sg--;
  
  	while (nents-- > 0) {
  		unsigned long vaddr;
  		long size;
  
  		DBG_RUN_SG(" %d : %08lx/%05x %08lx/%05x
  ", nents,
  			   (unsigned long)sg_dma_address(startsg), cnt,
  			   sg_virt_addr(startsg), startsg->length
  		);
  
  
  		/*
  		** Look for the start of a new DMA stream
  		*/
  		
  		if (sg_dma_address(startsg) & PIDE_FLAG) {
  			u32 pide = sg_dma_address(startsg) & ~PIDE_FLAG;
  
  			BUG_ON(pdirp && (dma_len != sg_dma_len(dma_sg)));
  
  			dma_sg++;
  
  			dma_len = sg_dma_len(startsg);
  			sg_dma_len(startsg) = 0;
  			dma_offset = (unsigned long) pide & ~IOVP_MASK;
  			n_mappings++;
  #if defined(ZX1_SUPPORT)
  			/* Pluto IOMMU IO Virt Address is not zero based */
  			sg_dma_address(dma_sg) = pide | ioc->ibase;
  #else
  			/* SBA, ccio, and dino are zero based.
  			 * Trying to save a few CPU cycles for most users.
  			 */
  			sg_dma_address(dma_sg) = pide;
  #endif
  			pdirp = &(ioc->pdir_base[pide >> IOVP_SHIFT]);
  			prefetchw(pdirp);
  		}
  		
  		BUG_ON(pdirp == NULL);
  		
  		vaddr = sg_virt_addr(startsg);
  		sg_dma_len(dma_sg) += startsg->length;
  		size = startsg->length + dma_offset;
  		dma_offset = 0;
  #ifdef IOMMU_MAP_STATS
  		ioc->msg_pages += startsg->length >> IOVP_SHIFT;
  #endif
  		do {
  			iommu_io_pdir_entry(pdirp, KERNEL_SPACE, 
  					    vaddr, hint);
  			vaddr += IOVP_SIZE;
  			size -= IOVP_SIZE;
  			pdirp++;
  		} while(unlikely(size > 0));
  		startsg++;
  	}
  	return(n_mappings);
  }
  
  
  /*
  ** First pass is to walk the SG list and determine where the breaks are
  ** in the DMA stream. Allocates PDIR entries but does not fill them.
  ** Returns the number of DMA chunks.
  **
  ** Doing the fill separate from the coalescing/allocation keeps the
  ** code simpler. Future enhancement could make one pass through
  ** the sglist do both.
  */
  
  static inline unsigned int

  iommu_coalesce_chunks(struct ioc *ioc, struct device *dev,

  		struct scatterlist *startsg, int nents,
  		int (*iommu_alloc_range)(struct ioc *, struct device *, size_t))

  {
  	struct scatterlist *contig_sg;	   /* contig chunk head */
  	unsigned long dma_offset, dma_len; /* start/len of DMA stream */
  	unsigned int n_mappings = 0;

  	unsigned int max_seg_size = dma_get_max_seg_size(dev);

  
  	while (nents > 0) {
  
  		/*
  		** Prepare for first/next DMA stream
  		*/
  		contig_sg = startsg;
  		dma_len = startsg->length;
  		dma_offset = sg_virt_addr(startsg) & ~IOVP_MASK;
  
  		/* PARANOID: clear entries */
  		sg_dma_address(startsg) = 0;
  		sg_dma_len(startsg) = 0;
  
  		/*
  		** This loop terminates one iteration "early" since
  		** it's always looking one "ahead".
  		*/
  		while(--nents > 0) {
  			unsigned long prevstartsg_end, startsg_end;
  
  			prevstartsg_end = sg_virt_addr(startsg) +
  				startsg->length;
  
  			startsg++;
  			startsg_end = sg_virt_addr(startsg) + 
  				startsg->length;
  
  			/* PARANOID: clear entries */
  			sg_dma_address(startsg) = 0;
  			sg_dma_len(startsg) = 0;
  
  			/*
  			** First make sure current dma stream won't
  			** exceed DMA_CHUNK_SIZE if we coalesce the
  			** next entry.
  			*/   

  			if(unlikely(ALIGN(dma_len + dma_offset + startsg->length,

  					    IOVP_SIZE) > DMA_CHUNK_SIZE))
  				break;

  			if (startsg->length + dma_len > max_seg_size)
  				break;

  			/*
  			** Next see if we can append the next chunk (i.e.
  			** it must end on one page and begin on another
  			*/
  			if (unlikely(((prevstartsg_end | sg_virt_addr(startsg)) & ~PAGE_MASK) != 0))
  				break;
  			
  			dma_len += startsg->length;
  		}
  
  		/*
  		** End of DMA Stream
  		** Terminate last VCONTIG block.
  		** Allocate space for DMA stream.
  		*/
  		sg_dma_len(contig_sg) = dma_len;

  		dma_len = ALIGN(dma_len + dma_offset, IOVP_SIZE);

  		sg_dma_address(contig_sg) =
  			PIDE_FLAG 

  			| (iommu_alloc_range(ioc, dev, dma_len) << IOVP_SHIFT)

  			| dma_offset;
  		n_mappings++;
  	}
  
  	return n_mappings;
  }