/*
   * Dynamic DMA mapping support.
   *

   * This implementation is a fallback for platforms that do not support

   * I/O TLBs (aka DMA address translation hardware).
   * Copyright (C) 2000 Asit Mallick <Asit.K.Mallick@intel.com>
   * Copyright (C) 2000 Goutham Rao <goutham.rao@intel.com>
   * Copyright (C) 2000, 2003 Hewlett-Packard Co
   *	David Mosberger-Tang <davidm@hpl.hp.com>
   *
   * 03/05/07 davidm	Switch from PCI-DMA to generic device DMA API.
   * 00/12/13 davidm	Rename to swiotlb.c and add mark_clean() to avoid
   *			unnecessary i-cache flushing.

   * 04/07/.. ak		Better overflow handling. Assorted fixes.
   * 05/09/10 linville	Add support for syncing ranges, support syncing for
   *			DMA_BIDIRECTIONAL mappings, miscellaneous cleanup.

   */
  
  #include <linux/cache.h>

  #include <linux/dma-mapping.h>

  #include <linux/mm.h>
  #include <linux/module.h>

  #include <linux/spinlock.h>
  #include <linux/string.h>
  #include <linux/types.h>
  #include <linux/ctype.h>
  
  #include <asm/io.h>

  #include <asm/dma.h>

  #include <asm/scatterlist.h>

  
  #include <linux/init.h>
  #include <linux/bootmem.h>
  
  #define OFFSET(val,align) ((unsigned long)	\
  	                   ( (val) & ( (align) - 1)))
  
  #define SG_ENT_VIRT_ADDRESS(sg)	(page_address((sg)->page) + (sg)->offset)

  #define SG_ENT_PHYS_ADDRESS(sg)	virt_to_bus(SG_ENT_VIRT_ADDRESS(sg))

  
  /*
   * Maximum allowable number of contiguous slabs to map,
   * must be a power of 2.  What is the appropriate value ?
   * The complexity of {map,unmap}_single is linearly dependent on this value.
   */
  #define IO_TLB_SEGSIZE	128
  
  /*
   * log of the size of each IO TLB slab.  The number of slabs is command line
   * controllable.
   */
  #define IO_TLB_SHIFT 11

  #define SLABS_PER_PAGE (1 << (PAGE_SHIFT - IO_TLB_SHIFT))
  
  /*
   * Minimum IO TLB size to bother booting with.  Systems with mainly
   * 64bit capable cards will only lightly use the swiotlb.  If we can't
   * allocate a contiguous 1MB, we're probably in trouble anyway.
   */
  #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)

  /*
   * Enumeration for sync targets
   */
  enum dma_sync_target {
  	SYNC_FOR_CPU = 0,
  	SYNC_FOR_DEVICE = 1,
  };

  int swiotlb_force;
  
  /*
   * Used to do a quick range check in swiotlb_unmap_single and
   * swiotlb_sync_single_*, to see if the memory was in fact allocated by this
   * API.
   */
  static char *io_tlb_start, *io_tlb_end;
  
  /*
   * The number of IO TLB blocks (in groups of 64) betweeen io_tlb_start and
   * io_tlb_end.  This is command line adjustable via setup_io_tlb_npages.
   */
  static unsigned long io_tlb_nslabs;
  
  /*
   * When the IOMMU overflows we return a fallback buffer. This sets the size.
   */
  static unsigned long io_tlb_overflow = 32*1024;
  
  void *io_tlb_overflow_buffer;
  
  /*
   * This is a free list describing the number of free entries available from
   * each index
   */
  static unsigned int *io_tlb_list;
  static unsigned int io_tlb_index;
  
  /*
   * We need to save away the original address corresponding to a mapped entry
   * for the sync operations.
   */

  static unsigned char **io_tlb_orig_addr;

  
  /*
   * Protect the above data structures in the map and unmap calls
   */
  static DEFINE_SPINLOCK(io_tlb_lock);
  
  static int __init
  setup_io_tlb_npages(char *str)
  {
  	if (isdigit(*str)) {

  		io_tlb_nslabs = simple_strtoul(str, &str, 0);

  		/* avoid tail segment of size < IO_TLB_SEGSIZE */
  		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
  	}
  	if (*str == ',')
  		++str;
  	if (!strcmp(str, "force"))
  		swiotlb_force = 1;
  	return 1;
  }
  __setup("swiotlb=", setup_io_tlb_npages);
  /* make io_tlb_overflow tunable too? */
  
  /*
   * Statically reserve bounce buffer space and initialize bounce buffer data

   * structures for the software IO TLB used to implement the DMA API.

   */

  void __init
  swiotlb_init_with_default_size(size_t default_size)

  {

  	unsigned long i, bytes;

  
  	if (!io_tlb_nslabs) {

  		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);

  		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
  	}

  	bytes = io_tlb_nslabs << IO_TLB_SHIFT;

  	/*
  	 * Get IO TLB memory from the low pages
  	 */

  	io_tlb_start = alloc_bootmem_low_pages(bytes);

  	if (!io_tlb_start)
  		panic("Cannot allocate SWIOTLB buffer");

  	io_tlb_end = io_tlb_start + bytes;

  
  	/*
  	 * Allocate and initialize the free list array.  This array is used
  	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
  	 * between io_tlb_start and io_tlb_end.
  	 */
  	io_tlb_list = alloc_bootmem(io_tlb_nslabs * sizeof(int));

  	for (i = 0; i < io_tlb_nslabs; i++)

   		io_tlb_list[i] = IO_TLB_SEGSIZE - OFFSET(i, IO_TLB_SEGSIZE);
  	io_tlb_index = 0;

  	io_tlb_orig_addr = alloc_bootmem(io_tlb_nslabs * sizeof(char *));

  
  	/*
  	 * Get the overflow emergency buffer
  	 */
  	io_tlb_overflow_buffer = alloc_bootmem_low(io_tlb_overflow);

  	if (!io_tlb_overflow_buffer)
  		panic("Cannot allocate SWIOTLB overflow buffer!
  ");

  	printk(KERN_INFO "Placing software IO TLB between 0x%lx - 0x%lx
  ",
  	       virt_to_bus(io_tlb_start), virt_to_bus(io_tlb_end));

  }

  void __init
  swiotlb_init(void)

  {

  	swiotlb_init_with_default_size(64 * (1<<20));	/* default to 64MB */

  }

  /*
   * Systems with larger DMA zones (those that don't support ISA) can
   * initialize the swiotlb later using the slab allocator if needed.
   * This should be just like above, but with some error catching.
   */
  int

  swiotlb_late_init_with_default_size(size_t default_size)

  {

  	unsigned long i, bytes, req_nslabs = io_tlb_nslabs;

  	unsigned int order;
  
  	if (!io_tlb_nslabs) {
  		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
  		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
  	}
  
  	/*
  	 * Get IO TLB memory from the low pages
  	 */

  	order = get_order(io_tlb_nslabs << IO_TLB_SHIFT);

  	io_tlb_nslabs = SLABS_PER_PAGE << order;

  	bytes = io_tlb_nslabs << IO_TLB_SHIFT;

  
  	while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
  		io_tlb_start = (char *)__get_free_pages(GFP_DMA | __GFP_NOWARN,
  		                                        order);
  		if (io_tlb_start)
  			break;
  		order--;
  	}
  
  	if (!io_tlb_start)
  		goto cleanup1;

  	if (order != get_order(bytes)) {

  		printk(KERN_WARNING "Warning: only able to allocate %ld MB "
  		       "for software IO TLB
  ", (PAGE_SIZE << order) >> 20);
  		io_tlb_nslabs = SLABS_PER_PAGE << order;

  		bytes = io_tlb_nslabs << IO_TLB_SHIFT;

  	}

  	io_tlb_end = io_tlb_start + bytes;
  	memset(io_tlb_start, 0, bytes);

  
  	/*
  	 * Allocate and initialize the free list array.  This array is used
  	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
  	 * between io_tlb_start and io_tlb_end.
  	 */
  	io_tlb_list = (unsigned int *)__get_free_pages(GFP_KERNEL,
  	                              get_order(io_tlb_nslabs * sizeof(int)));
  	if (!io_tlb_list)
  		goto cleanup2;
  
  	for (i = 0; i < io_tlb_nslabs; i++)
   		io_tlb_list[i] = IO_TLB_SEGSIZE - OFFSET(i, IO_TLB_SEGSIZE);
  	io_tlb_index = 0;

  	io_tlb_orig_addr = (unsigned char **)__get_free_pages(GFP_KERNEL,
  	                           get_order(io_tlb_nslabs * sizeof(char *)));

  	if (!io_tlb_orig_addr)
  		goto cleanup3;

  	memset(io_tlb_orig_addr, 0, io_tlb_nslabs * sizeof(char *));

  
  	/*
  	 * Get the overflow emergency buffer
  	 */
  	io_tlb_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
  	                                          get_order(io_tlb_overflow));
  	if (!io_tlb_overflow_buffer)
  		goto cleanup4;

  	printk(KERN_INFO "Placing %luMB software IO TLB between 0x%lx - "
  	       "0x%lx
  ", bytes >> 20,
  	       virt_to_bus(io_tlb_start), virt_to_bus(io_tlb_end));

  
  	return 0;
  
  cleanup4:

  	free_pages((unsigned long)io_tlb_orig_addr, get_order(io_tlb_nslabs *
  	                                                      sizeof(char *)));

  	io_tlb_orig_addr = NULL;
  cleanup3:

  	free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
  	                                                 sizeof(int)));

  	io_tlb_list = NULL;

  cleanup2:

  	io_tlb_end = NULL;

  	free_pages((unsigned long)io_tlb_start, order);
  	io_tlb_start = NULL;
  cleanup1:
  	io_tlb_nslabs = req_nslabs;
  	return -ENOMEM;
  }

  static int

  address_needs_mapping(struct device *hwdev, dma_addr_t addr)
  {
  	dma_addr_t mask = 0xffffffff;
  	/* If the device has a mask, use it, otherwise default to 32 bits */
  	if (hwdev && hwdev->dma_mask)
  		mask = *hwdev->dma_mask;
  	return (addr & ~mask) != 0;
  }
  
  /*
   * Allocates bounce buffer and returns its kernel virtual address.
   */
  static void *

  map_single(struct device *hwdev, char *buffer, size_t size, int dir)

  {
  	unsigned long flags;
  	char *dma_addr;
  	unsigned int nslots, stride, index, wrap;
  	int i;
  
  	/*
  	 * For mappings greater than a page, we limit the stride (and
  	 * hence alignment) to a page size.
  	 */
  	nslots = ALIGN(size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
  	if (size > PAGE_SIZE)
  		stride = (1 << (PAGE_SHIFT - IO_TLB_SHIFT));
  	else
  		stride = 1;

  	BUG_ON(!nslots);

  
  	/*
  	 * Find suitable number of IO TLB entries size that will fit this
  	 * request and allocate a buffer from that IO TLB pool.
  	 */
  	spin_lock_irqsave(&io_tlb_lock, flags);
  	{
  		wrap = index = ALIGN(io_tlb_index, stride);
  
  		if (index >= io_tlb_nslabs)
  			wrap = index = 0;
  
  		do {
  			/*
  			 * If we find a slot that indicates we have 'nslots'
  			 * number of contiguous buffers, we allocate the
  			 * buffers from that slot and mark the entries as '0'
  			 * indicating unavailable.
  			 */
  			if (io_tlb_list[index] >= nslots) {
  				int count = 0;
  
  				for (i = index; i < (int) (index + nslots); i++)
  					io_tlb_list[i] = 0;
  				for (i = index - 1; (OFFSET(i, IO_TLB_SEGSIZE) != IO_TLB_SEGSIZE -1) && io_tlb_list[i]; i--)
  					io_tlb_list[i] = ++count;
  				dma_addr = io_tlb_start + (index << IO_TLB_SHIFT);
  
  				/*
  				 * Update the indices to avoid searching in
  				 * the next round.
  				 */
  				io_tlb_index = ((index + nslots) < io_tlb_nslabs
  						? (index + nslots) : 0);
  
  				goto found;
  			}
  			index += stride;
  			if (index >= io_tlb_nslabs)
  				index = 0;
  		} while (index != wrap);
  
  		spin_unlock_irqrestore(&io_tlb_lock, flags);
  		return NULL;
  	}
    found:
  	spin_unlock_irqrestore(&io_tlb_lock, flags);
  
  	/*
  	 * Save away the mapping from the original address to the DMA address.
  	 * This is needed when we sync the memory.  Then we sync the buffer if
  	 * needed.
  	 */
  	io_tlb_orig_addr[index] = buffer;
  	if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)

  		memcpy(dma_addr, buffer, size);

  
  	return dma_addr;
  }
  
  /*
   * dma_addr is the kernel virtual address of the bounce buffer to unmap.
   */
  static void
  unmap_single(struct device *hwdev, char *dma_addr, size_t size, int dir)
  {
  	unsigned long flags;
  	int i, count, nslots = ALIGN(size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
  	int index = (dma_addr - io_tlb_start) >> IO_TLB_SHIFT;

  	char *buffer = io_tlb_orig_addr[index];

  
  	/*
  	 * First, sync the memory before unmapping the entry
  	 */

  	if (buffer && ((dir == DMA_FROM_DEVICE) || (dir == DMA_BIDIRECTIONAL)))

  		/*
  		 * bounce... copy the data back into the original buffer * and
  		 * delete the bounce buffer.
  		 */

  		memcpy(buffer, dma_addr, size);

  
  	/*
  	 * Return the buffer to the free list by setting the corresponding
  	 * entries to indicate the number of contigous entries available.
  	 * While returning the entries to the free list, we merge the entries
  	 * with slots below and above the pool being returned.
  	 */
  	spin_lock_irqsave(&io_tlb_lock, flags);
  	{
  		count = ((index + nslots) < ALIGN(index + 1, IO_TLB_SEGSIZE) ?
  			 io_tlb_list[index + nslots] : 0);
  		/*
  		 * Step 1: return the slots to the free list, merging the
  		 * slots with superceeding slots
  		 */
  		for (i = index + nslots - 1; i >= index; i--)
  			io_tlb_list[i] = ++count;
  		/*
  		 * Step 2: merge the returned slots with the preceding slots,
  		 * if available (non zero)
  		 */
  		for (i = index - 1; (OFFSET(i, IO_TLB_SEGSIZE) != IO_TLB_SEGSIZE -1) && io_tlb_list[i]; i--)
  			io_tlb_list[i] = ++count;
  	}
  	spin_unlock_irqrestore(&io_tlb_lock, flags);
  }
  
  static void

  sync_single(struct device *hwdev, char *dma_addr, size_t size,
  	    int dir, int target)

  {
  	int index = (dma_addr - io_tlb_start) >> IO_TLB_SHIFT;

  	char *buffer = io_tlb_orig_addr[index];

  	switch (target) {
  	case SYNC_FOR_CPU:
  		if (likely(dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL))

  			memcpy(buffer, dma_addr, size);

  		else
  			BUG_ON(dir != DMA_TO_DEVICE);

  		break;
  	case SYNC_FOR_DEVICE:
  		if (likely(dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))

  			memcpy(dma_addr, buffer, size);

  		else
  			BUG_ON(dir != DMA_FROM_DEVICE);

  		break;
  	default:

  		BUG();

  	}

  }
  
  void *
  swiotlb_alloc_coherent(struct device *hwdev, size_t size,

  		       dma_addr_t *dma_handle, gfp_t flags)

  {

  	dma_addr_t dev_addr;

  	void *ret;
  	int order = get_order(size);
  
  	/*
  	 * XXX fix me: the DMA API should pass us an explicit DMA mask
  	 * instead, or use ZONE_DMA32 (ia64 overloads ZONE_DMA to be a ~32
  	 * bit range instead of a 16MB one).
  	 */
  	flags |= GFP_DMA;

  	ret = (void *)__get_free_pages(flags, order);

  	if (ret && address_needs_mapping(hwdev, virt_to_bus(ret))) {

  		/*
  		 * The allocated memory isn't reachable by the device.
  		 * Fall back on swiotlb_map_single().
  		 */
  		free_pages((unsigned long) ret, order);
  		ret = NULL;
  	}
  	if (!ret) {
  		/*
  		 * We are either out of memory or the device can't DMA
  		 * to GFP_DMA memory; fall back on
  		 * swiotlb_map_single(), which will grab memory from
  		 * the lowest available address range.
  		 */
  		dma_addr_t handle;
  		handle = swiotlb_map_single(NULL, NULL, size, DMA_FROM_DEVICE);

  		if (swiotlb_dma_mapping_error(handle))

  			return NULL;

  		ret = bus_to_virt(handle);

  	}
  
  	memset(ret, 0, size);

  	dev_addr = virt_to_bus(ret);

  
  	/* Confirm address can be DMA'd by device */
  	if (address_needs_mapping(hwdev, dev_addr)) {

  		printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx
  ",
  		       (unsigned long long)*hwdev->dma_mask,
  		       (unsigned long long)dev_addr);

  		panic("swiotlb_alloc_coherent: allocated memory is out of "
  		      "range for device");
  	}
  	*dma_handle = dev_addr;
  	return ret;
  }
  
  void
  swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
  		      dma_addr_t dma_handle)
  {
  	if (!(vaddr >= (void *)io_tlb_start
                      && vaddr < (void *)io_tlb_end))
  		free_pages((unsigned long) vaddr, get_order(size));
  	else
  		/* DMA_TO_DEVICE to avoid memcpy in unmap_single */
  		swiotlb_unmap_single (hwdev, dma_handle, size, DMA_TO_DEVICE);
  }
  
  static void
  swiotlb_full(struct device *dev, size_t size, int dir, int do_panic)
  {
  	/*
  	 * Ran out of IOMMU space for this operation. This is very bad.
  	 * Unfortunately the drivers cannot handle this operation properly.

  	 * unless they check for dma_mapping_error (most don't)

  	 * When the mapping is small enough return a static buffer to limit
  	 * the damage, or panic when the transfer is too big.
  	 */

  	printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "

  	       "device %s
  ", size, dev ? dev->bus_id : "?");
  
  	if (size > io_tlb_overflow && do_panic) {

  		if (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)
  			panic("DMA: Memory would be corrupted
  ");
  		if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
  			panic("DMA: Random memory would be DMAed
  ");

  	}
  }
  
  /*
   * Map a single buffer of the indicated size for DMA in streaming mode.  The

   * physical address to use is returned.

   *
   * Once the device is given the dma address, the device owns this memory until
   * either swiotlb_unmap_single or swiotlb_dma_sync_single is performed.
   */
  dma_addr_t
  swiotlb_map_single(struct device *hwdev, void *ptr, size_t size, int dir)
  {

  	dma_addr_t dev_addr = virt_to_bus(ptr);

  	void *map;

  	BUG_ON(dir == DMA_NONE);

  	/*
  	 * If the pointer passed in happens to be in the device's DMA window,
  	 * we can safely return the device addr and not worry about bounce
  	 * buffering it.
  	 */

  	if (!address_needs_mapping(hwdev, dev_addr) && !swiotlb_force)

  		return dev_addr;
  
  	/*
  	 * Oh well, have to allocate and map a bounce buffer.
  	 */

  	map = map_single(hwdev, ptr, size, dir);

  	if (!map) {
  		swiotlb_full(hwdev, size, dir, 1);
  		map = io_tlb_overflow_buffer;
  	}

  	dev_addr = virt_to_bus(map);

  
  	/*
  	 * Ensure that the address returned is DMA'ble
  	 */
  	if (address_needs_mapping(hwdev, dev_addr))
  		panic("map_single: bounce buffer is not DMA'ble");
  
  	return dev_addr;
  }
  
  /*

   * Unmap a single streaming mode DMA translation.  The dma_addr and size must
   * match what was provided for in a previous swiotlb_map_single call.  All
   * other usages are undefined.
   *
   * After this call, reads by the cpu to the buffer are guaranteed to see
   * whatever the device wrote there.
   */
  void
  swiotlb_unmap_single(struct device *hwdev, dma_addr_t dev_addr, size_t size,
  		     int dir)
  {

  	char *dma_addr = bus_to_virt(dev_addr);

  	BUG_ON(dir == DMA_NONE);

  	if (dma_addr >= io_tlb_start && dma_addr < io_tlb_end)
  		unmap_single(hwdev, dma_addr, size, dir);
  	else if (dir == DMA_FROM_DEVICE)

  		dma_mark_clean(dma_addr, size);

  }
  
  /*
   * Make physical memory consistent for a single streaming mode DMA translation
   * after a transfer.
   *
   * If you perform a swiotlb_map_single() but wish to interrogate the buffer

   * using the cpu, yet do not wish to teardown the dma mapping, you must
   * call this function before doing so.  At the next point you give the dma

   * address back to the card, you must first perform a
   * swiotlb_dma_sync_for_device, and then the device again owns the buffer
   */

  static void

  swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,

  		    size_t size, int dir, int target)

  {

  	char *dma_addr = bus_to_virt(dev_addr);

  	BUG_ON(dir == DMA_NONE);

  	if (dma_addr >= io_tlb_start && dma_addr < io_tlb_end)

  		sync_single(hwdev, dma_addr, size, dir, target);

  	else if (dir == DMA_FROM_DEVICE)

  		dma_mark_clean(dma_addr, size);

  }
  
  void

  swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,
  			    size_t size, int dir)
  {

  	swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_CPU);

  }
  
  void

  swiotlb_sync_single_for_device(struct device *hwdev, dma_addr_t dev_addr,
  			       size_t size, int dir)
  {

  	swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_DEVICE);

  }
  
  /*

   * Same as above, but for a sub-range of the mapping.
   */

  static void

  swiotlb_sync_single_range(struct device *hwdev, dma_addr_t dev_addr,

  			  unsigned long offset, size_t size,
  			  int dir, int target)

  {

  	char *dma_addr = bus_to_virt(dev_addr) + offset;

  	BUG_ON(dir == DMA_NONE);

  	if (dma_addr >= io_tlb_start && dma_addr < io_tlb_end)

  		sync_single(hwdev, dma_addr, size, dir, target);

  	else if (dir == DMA_FROM_DEVICE)

  		dma_mark_clean(dma_addr, size);

  }
  
  void
  swiotlb_sync_single_range_for_cpu(struct device *hwdev, dma_addr_t dev_addr,
  				  unsigned long offset, size_t size, int dir)
  {

  	swiotlb_sync_single_range(hwdev, dev_addr, offset, size, dir,
  				  SYNC_FOR_CPU);

  }
  
  void
  swiotlb_sync_single_range_for_device(struct device *hwdev, dma_addr_t dev_addr,
  				     unsigned long offset, size_t size, int dir)
  {

  	swiotlb_sync_single_range(hwdev, dev_addr, offset, size, dir,
  				  SYNC_FOR_DEVICE);

  }
  
  /*

   * Map a set of buffers described by scatterlist in streaming mode for DMA.
   * This is the scatter-gather version of the above swiotlb_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 swiotlb_map_single are the
   * same here.
   */
  int
  swiotlb_map_sg(struct device *hwdev, struct scatterlist *sg, int nelems,
  	       int dir)
  {

  	void *addr;

  	dma_addr_t dev_addr;

  	int i;

  	BUG_ON(dir == DMA_NONE);

  
  	for (i = 0; i < nelems; i++, sg++) {

  		addr = SG_ENT_VIRT_ADDRESS(sg);
  		dev_addr = virt_to_bus(addr);
  		if (swiotlb_force || address_needs_mapping(hwdev, dev_addr)) {
  			void *map = map_single(hwdev, addr, sg->length, dir);

  			if (!map) {

  				/* Don't panic here, we expect map_sg users
  				   to do proper error handling. */
  				swiotlb_full(hwdev, sg->length, dir, 0);
  				swiotlb_unmap_sg(hwdev, sg - i, i, dir);
  				sg[0].dma_length = 0;
  				return 0;
  			}

  			sg->dma_address = virt_to_bus(map);

  		} else
  			sg->dma_address = dev_addr;
  		sg->dma_length = sg->length;
  	}
  	return nelems;
  }
  
  /*
   * Unmap a set of streaming mode DMA translations.  Again, cpu read rules
   * concerning calls here are the same as for swiotlb_unmap_single() above.
   */
  void
  swiotlb_unmap_sg(struct device *hwdev, struct scatterlist *sg, int nelems,
  		 int dir)
  {
  	int i;

  	BUG_ON(dir == DMA_NONE);

  
  	for (i = 0; i < nelems; i++, sg++)
  		if (sg->dma_address != SG_ENT_PHYS_ADDRESS(sg))

  			unmap_single(hwdev, bus_to_virt(sg->dma_address),
  				     sg->dma_length, dir);

  		else if (dir == DMA_FROM_DEVICE)

  			dma_mark_clean(SG_ENT_VIRT_ADDRESS(sg), sg->dma_length);

  }
  
  /*
   * Make physical memory consistent for a set of streaming mode DMA translations
   * after a transfer.
   *
   * The same as swiotlb_sync_single_* but for a scatter-gather list, same rules
   * and usage.
   */

  static void

  swiotlb_sync_sg(struct device *hwdev, struct scatterlist *sg,

  		int nelems, int dir, int target)

  {
  	int i;

  	BUG_ON(dir == DMA_NONE);

  
  	for (i = 0; i < nelems; i++, sg++)
  		if (sg->dma_address != SG_ENT_PHYS_ADDRESS(sg))

  			sync_single(hwdev, bus_to_virt(sg->dma_address),

  				    sg->dma_length, dir, target);

  		else if (dir == DMA_FROM_DEVICE)
  			dma_mark_clean(SG_ENT_VIRT_ADDRESS(sg), sg->dma_length);

  }
  
  void

  swiotlb_sync_sg_for_cpu(struct device *hwdev, struct scatterlist *sg,
  			int nelems, int dir)
  {

  	swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_CPU);

  }
  
  void

  swiotlb_sync_sg_for_device(struct device *hwdev, struct scatterlist *sg,
  			   int nelems, int dir)
  {

  	swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_DEVICE);

  }
  
  int
  swiotlb_dma_mapping_error(dma_addr_t dma_addr)
  {

  	return (dma_addr == virt_to_bus(io_tlb_overflow_buffer));

  }
  
  /*

   * Return whether the given device DMA address mask can be supported

   * properly.  For example, if your device can only drive the low 24-bits

   * during bus mastering, then you would pass 0x00ffffff as the mask to

   * this function.
   */
  int

  swiotlb_dma_supported(struct device *hwdev, u64 mask)

  {

  	return virt_to_bus(io_tlb_end - 1) <= mask;

  }
  
  EXPORT_SYMBOL(swiotlb_init);
  EXPORT_SYMBOL(swiotlb_map_single);
  EXPORT_SYMBOL(swiotlb_unmap_single);
  EXPORT_SYMBOL(swiotlb_map_sg);
  EXPORT_SYMBOL(swiotlb_unmap_sg);
  EXPORT_SYMBOL(swiotlb_sync_single_for_cpu);
  EXPORT_SYMBOL(swiotlb_sync_single_for_device);

  EXPORT_SYMBOL_GPL(swiotlb_sync_single_range_for_cpu);
  EXPORT_SYMBOL_GPL(swiotlb_sync_single_range_for_device);

  EXPORT_SYMBOL(swiotlb_sync_sg_for_cpu);
  EXPORT_SYMBOL(swiotlb_sync_sg_for_device);
  EXPORT_SYMBOL(swiotlb_dma_mapping_error);

  EXPORT_SYMBOL(swiotlb_alloc_coherent);
  EXPORT_SYMBOL(swiotlb_free_coherent);

  EXPORT_SYMBOL(swiotlb_dma_supported);