/*
   * 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.

   * 08/12/11 beckyb	Add highmem support

   */
  
  #include <linux/cache.h>

  #include <linux/dma-mapping.h>

  #include <linux/mm.h>

  #include <linux/export.h>

  #include <linux/spinlock.h>
  #include <linux/string.h>

  #include <linux/swiotlb.h>

  #include <linux/pfn.h>

  #include <linux/types.h>
  #include <linux/ctype.h>

  #include <linux/highmem.h>

  #include <linux/gfp.h>

  #include <linux/scatterlist.h>

  #include <linux/mem_encrypt.h>

  
  #include <asm/io.h>

  #include <asm/dma.h>
  
  #include <linux/init.h>
  #include <linux/bootmem.h>

  #include <linux/iommu-helper.h>

  #define CREATE_TRACE_POINTS

  #include <trace/events/swiotlb.h>

  #define OFFSET(val,align) ((unsigned long)	\
  	                   ( (val) & ( (align) - 1)))

  #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)

  enum swiotlb_force swiotlb_force;

  
  /*

   * Used to do a quick range check in swiotlb_tbl_unmap_single and
   * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this

   * API.
   */

  static phys_addr_t io_tlb_start, io_tlb_end;

  
  /*

   * The number of IO TLB blocks (in groups of 64) between 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;

  static phys_addr_t 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;
  
  /*

   * Max segment that we can provide which (if pages are contingous) will
   * not be bounced (unless SWIOTLB_FORCE is set).
   */
  unsigned int max_segment;
  
  /*

   * We need to save away the original address corresponding to a mapped entry
   * for the sync operations.
   */

  #define INVALID_PHYS_ADDR (~(phys_addr_t)0)

  static phys_addr_t *io_tlb_orig_addr;

  
  /*
   * Protect the above data structures in the map and unmap calls
   */
  static DEFINE_SPINLOCK(io_tlb_lock);

  static int late_alloc;

  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 = SWIOTLB_FORCE;

  	} else if (!strcmp(str, "noforce")) {
  		swiotlb_force = SWIOTLB_NO_FORCE;
  		io_tlb_nslabs = 1;
  	}

  	return 0;

  }

  early_param("swiotlb", setup_io_tlb_npages);

  /* make io_tlb_overflow tunable too? */

  unsigned long swiotlb_nr_tbl(void)

  {
  	return io_tlb_nslabs;
  }

  EXPORT_SYMBOL_GPL(swiotlb_nr_tbl);

  unsigned int swiotlb_max_segment(void)
  {
  	return max_segment;
  }
  EXPORT_SYMBOL_GPL(swiotlb_max_segment);
  
  void swiotlb_set_max_segment(unsigned int val)
  {
  	if (swiotlb_force == SWIOTLB_FORCE)
  		max_segment = 1;
  	else
  		max_segment = rounddown(val, PAGE_SIZE);
  }

  /* default to 64MB */
  #define IO_TLB_DEFAULT_SIZE (64UL<<20)
  unsigned long swiotlb_size_or_default(void)
  {
  	unsigned long size;
  
  	size = io_tlb_nslabs << IO_TLB_SHIFT;
  
  	return size ? size : (IO_TLB_DEFAULT_SIZE);
  }

  void __weak swiotlb_set_mem_attributes(void *vaddr, unsigned long size) { }
  
  /* For swiotlb, clear memory encryption mask from dma addresses */
  static dma_addr_t swiotlb_phys_to_dma(struct device *hwdev,
  				      phys_addr_t address)
  {
  	return __sme_clr(phys_to_dma(hwdev, address));
  }

  /* Note that this doesn't work with highmem page */

  static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
  				      volatile void *address)

  {

  	return phys_to_dma(hwdev, virt_to_phys(address));

  }

  static bool no_iotlb_memory;

  void swiotlb_print_info(void)

  {

  	unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;

  	unsigned char *vstart, *vend;

  	if (no_iotlb_memory) {
  		pr_warn("software IO TLB: No low mem
  ");
  		return;
  	}

  	vstart = phys_to_virt(io_tlb_start);

  	vend = phys_to_virt(io_tlb_end);

  	printk(KERN_INFO "software IO TLB [mem %#010llx-%#010llx] (%luMB) mapped at [%p-%p]
  ",

  	       (unsigned long long)io_tlb_start,

  	       (unsigned long long)io_tlb_end,

  	       bytes >> 20, vstart, vend - 1);

  }

  /*
   * Early SWIOTLB allocation may be too early to allow an architecture to
   * perform the desired operations.  This function allows the architecture to
   * call SWIOTLB when the operations are possible.  It needs to be called
   * before the SWIOTLB memory is used.
   */
  void __init swiotlb_update_mem_attributes(void)
  {
  	void *vaddr;
  	unsigned long bytes;
  
  	if (no_iotlb_memory || late_alloc)
  		return;
  
  	vaddr = phys_to_virt(io_tlb_start);
  	bytes = PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT);
  	swiotlb_set_mem_attributes(vaddr, bytes);
  	memset(vaddr, 0, bytes);
  
  	vaddr = phys_to_virt(io_tlb_overflow_buffer);
  	bytes = PAGE_ALIGN(io_tlb_overflow);
  	swiotlb_set_mem_attributes(vaddr, bytes);
  	memset(vaddr, 0, bytes);
  }

  int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)

  {

  	void *v_overflow_buffer;

  	unsigned long i, bytes;

  	bytes = nslabs << IO_TLB_SHIFT;

  	io_tlb_nslabs = nslabs;

  	io_tlb_start = __pa(tlb);
  	io_tlb_end = io_tlb_start + bytes;

  
  	/*

  	 * Get the overflow emergency buffer
  	 */

  	v_overflow_buffer = memblock_virt_alloc_low_nopanic(

  						PAGE_ALIGN(io_tlb_overflow),
  						PAGE_SIZE);

  	if (!v_overflow_buffer)

  		return -ENOMEM;

  
  	io_tlb_overflow_buffer = __pa(v_overflow_buffer);
  
  	/*

  	 * 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 = memblock_virt_alloc(
  				PAGE_ALIGN(io_tlb_nslabs * sizeof(int)),
  				PAGE_SIZE);

  	io_tlb_orig_addr = memblock_virt_alloc(
  				PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)),
  				PAGE_SIZE);

  	for (i = 0; i < io_tlb_nslabs; i++) {
  		io_tlb_list[i] = IO_TLB_SEGSIZE - OFFSET(i, IO_TLB_SEGSIZE);
  		io_tlb_orig_addr[i] = INVALID_PHYS_ADDR;
  	}
  	io_tlb_index = 0;

  	if (verbose)
  		swiotlb_print_info();

  	swiotlb_set_max_segment(io_tlb_nslabs << IO_TLB_SHIFT);

  	return 0;

  }

  /*
   * 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(int verbose)

  {

  	size_t default_size = IO_TLB_DEFAULT_SIZE;

  	unsigned char *vstart;

  	unsigned long 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 */

  	vstart = memblock_virt_alloc_low_nopanic(PAGE_ALIGN(bytes), PAGE_SIZE);

  	if (vstart && !swiotlb_init_with_tbl(vstart, io_tlb_nslabs, verbose))
  		return;

  	if (io_tlb_start)

  		memblock_free_early(io_tlb_start,
  				    PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));

  	pr_warn("Cannot allocate SWIOTLB buffer");
  	no_iotlb_memory = true;

  }

  /*
   * 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 bytes, req_nslabs = io_tlb_nslabs;

  	unsigned char *vstart = NULL;

  	unsigned int order;

  	int rc = 0;

  
  	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) {

  		vstart = (void *)__get_free_pages(GFP_DMA | __GFP_NOWARN,
  						  order);
  		if (vstart)

  			break;
  		order--;
  	}

  	if (!vstart) {

  		io_tlb_nslabs = req_nslabs;
  		return -ENOMEM;
  	}

  	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;
  	}

  	rc = swiotlb_late_init_with_tbl(vstart, io_tlb_nslabs);

  	if (rc)

  		free_pages((unsigned long)vstart, order);

  	return rc;
  }
  
  int
  swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
  {
  	unsigned long i, bytes;

  	unsigned char *v_overflow_buffer;

  
  	bytes = nslabs << IO_TLB_SHIFT;
  
  	io_tlb_nslabs = nslabs;

  	io_tlb_start = virt_to_phys(tlb);
  	io_tlb_end = io_tlb_start + bytes;

  	swiotlb_set_mem_attributes(tlb, bytes);

  	memset(tlb, 0, bytes);

  
  	/*

  	 * Get the overflow emergency buffer
  	 */
  	v_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
  						     get_order(io_tlb_overflow));
  	if (!v_overflow_buffer)
  		goto cleanup2;

  	swiotlb_set_mem_attributes(v_overflow_buffer, io_tlb_overflow);
  	memset(v_overflow_buffer, 0, io_tlb_overflow);

  	io_tlb_overflow_buffer = virt_to_phys(v_overflow_buffer);
  
  	/*

  	 * 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 cleanup3;

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

  	if (!io_tlb_orig_addr)

  		goto cleanup4;

  	for (i = 0; i < io_tlb_nslabs; i++) {
  		io_tlb_list[i] = IO_TLB_SEGSIZE - OFFSET(i, IO_TLB_SEGSIZE);
  		io_tlb_orig_addr[i] = INVALID_PHYS_ADDR;
  	}
  	io_tlb_index = 0;

  	swiotlb_print_info();

  	late_alloc = 1;

  	swiotlb_set_max_segment(io_tlb_nslabs << IO_TLB_SHIFT);

  	return 0;
  
  cleanup4:

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

  	io_tlb_list = NULL;

  cleanup3:
  	free_pages((unsigned long)v_overflow_buffer,
  		   get_order(io_tlb_overflow));
  	io_tlb_overflow_buffer = 0;

  cleanup2:

  	io_tlb_end = 0;

  	io_tlb_start = 0;

  	io_tlb_nslabs = 0;

  	max_segment = 0;

  	return -ENOMEM;
  }

  void __init swiotlb_free(void)
  {

  	if (!io_tlb_orig_addr)

  		return;
  
  	if (late_alloc) {

  		free_pages((unsigned long)phys_to_virt(io_tlb_overflow_buffer),

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

  		free_pages((unsigned long)phys_to_virt(io_tlb_start),

  			   get_order(io_tlb_nslabs << IO_TLB_SHIFT));
  	} else {

  		memblock_free_late(io_tlb_overflow_buffer,
  				   PAGE_ALIGN(io_tlb_overflow));
  		memblock_free_late(__pa(io_tlb_orig_addr),
  				   PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
  		memblock_free_late(__pa(io_tlb_list),
  				   PAGE_ALIGN(io_tlb_nslabs * sizeof(int)));
  		memblock_free_late(io_tlb_start,
  				   PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));

  	}

  	io_tlb_nslabs = 0;

  	max_segment = 0;

  }

  int is_swiotlb_buffer(phys_addr_t paddr)

  {

  	return paddr >= io_tlb_start && paddr < io_tlb_end;

  }

  /*

   * Bounce: copy the swiotlb buffer back to the original dma location
   */

  static void swiotlb_bounce(phys_addr_t orig_addr, phys_addr_t tlb_addr,
  			   size_t size, enum dma_data_direction dir)

  {

  	unsigned long pfn = PFN_DOWN(orig_addr);
  	unsigned char *vaddr = phys_to_virt(tlb_addr);

  
  	if (PageHighMem(pfn_to_page(pfn))) {
  		/* The buffer does not have a mapping.  Map it in and copy */

  		unsigned int offset = orig_addr & ~PAGE_MASK;

  		char *buffer;
  		unsigned int sz = 0;
  		unsigned long flags;
  
  		while (size) {

  			sz = min_t(size_t, PAGE_SIZE - offset, size);

  
  			local_irq_save(flags);

  			buffer = kmap_atomic(pfn_to_page(pfn));

  			if (dir == DMA_TO_DEVICE)

  				memcpy(vaddr, buffer + offset, sz);

  			else

  				memcpy(buffer + offset, vaddr, sz);

  			kunmap_atomic(buffer);

  			local_irq_restore(flags);

  
  			size -= sz;
  			pfn++;

  			vaddr += sz;

  			offset = 0;

  		}

  	} else if (dir == DMA_TO_DEVICE) {
  		memcpy(vaddr, phys_to_virt(orig_addr), size);

  	} else {

  		memcpy(phys_to_virt(orig_addr), vaddr, size);

  	}

  }

  phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
  				   dma_addr_t tbl_dma_addr,
  				   phys_addr_t orig_addr, size_t size,

  				   enum dma_data_direction dir,
  				   unsigned long attrs)

  {
  	unsigned long flags;

  	phys_addr_t tlb_addr;

  	unsigned int nslots, stride, index, wrap;
  	int i;

  	unsigned long mask;
  	unsigned long offset_slots;
  	unsigned long max_slots;

  	if (no_iotlb_memory)
  		panic("Can not allocate SWIOTLB buffer earlier and can't now provide you with the DMA bounce buffer");

  	if (sme_active())
  		pr_warn_once("SME is active and system is using DMA bounce buffers
  ");

  	mask = dma_get_seg_boundary(hwdev);

  	tbl_dma_addr &= mask;
  
  	offset_slots = ALIGN(tbl_dma_addr, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;

  
  	/*
   	 * Carefully handle integer overflow which can occur when mask == ~0UL.
   	 */

  	max_slots = mask + 1
  		    ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
  		    : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);

  
  	/*

  	 * For mappings greater than or equal to 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);

  	index = ALIGN(io_tlb_index, stride);
  	if (index >= io_tlb_nslabs)
  		index = 0;
  	wrap = index;
  
  	do {

  		while (iommu_is_span_boundary(index, nslots, offset_slots,
  					      max_slots)) {

  			index += stride;
  			if (index >= io_tlb_nslabs)
  				index = 0;

  			if (index == wrap)
  				goto not_found;
  		}
  
  		/*
  		 * 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;

  			tlb_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);
  
  not_found:
  	spin_unlock_irqrestore(&io_tlb_lock, flags);

  	if (!(attrs & DMA_ATTR_NO_WARN) && printk_ratelimit())

  		dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)
  ", size);

  	return SWIOTLB_MAP_ERROR;

  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.
  	 */

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

  		io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);

  	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
  	    (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))

  		swiotlb_bounce(orig_addr, tlb_addr, size, DMA_TO_DEVICE);

  	return tlb_addr;

  }

  EXPORT_SYMBOL_GPL(swiotlb_tbl_map_single);

  
  /*

   * Allocates bounce buffer and returns its kernel virtual address.
   */

  static phys_addr_t
  map_single(struct device *hwdev, phys_addr_t phys, size_t size,

  	   enum dma_data_direction dir, unsigned long attrs)

  {

  	dma_addr_t start_dma_addr;
  
  	if (swiotlb_force == SWIOTLB_NO_FORCE) {
  		dev_warn_ratelimited(hwdev, "Cannot do DMA to address %pa
  ",
  				     &phys);
  		return SWIOTLB_MAP_ERROR;
  	}

  	start_dma_addr = swiotlb_phys_to_dma(hwdev, io_tlb_start);

  	return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size,
  				      dir, attrs);

  }
  
  /*

   * dma_addr is the kernel virtual address of the bounce buffer to unmap.
   */

  void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,

  			      size_t size, enum dma_data_direction dir,
  			      unsigned long attrs)

  {
  	unsigned long flags;
  	int i, count, nslots = ALIGN(size, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;

  	int index = (tlb_addr - io_tlb_start) >> IO_TLB_SHIFT;
  	phys_addr_t orig_addr = io_tlb_orig_addr[index];

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

  	if (orig_addr != INVALID_PHYS_ADDR &&

  	    !(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&

  	    ((dir == DMA_FROM_DEVICE) || (dir == DMA_BIDIRECTIONAL)))

  		swiotlb_bounce(orig_addr, tlb_addr, size, DMA_FROM_DEVICE);

  
  	/*
  	 * Return the buffer to the free list by setting the corresponding

  	 * entries to indicate the number of contiguous 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;

  			io_tlb_orig_addr[i] = INVALID_PHYS_ADDR;
  		}

  		/*
  		 * 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);
  }

  EXPORT_SYMBOL_GPL(swiotlb_tbl_unmap_single);

  void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr,
  			     size_t size, enum dma_data_direction dir,
  			     enum dma_sync_target target)

  {

  	int index = (tlb_addr - io_tlb_start) >> IO_TLB_SHIFT;
  	phys_addr_t orig_addr = io_tlb_orig_addr[index];

  	if (orig_addr == INVALID_PHYS_ADDR)
  		return;

  	orig_addr += (unsigned long)tlb_addr & ((1 << IO_TLB_SHIFT) - 1);

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

  			swiotlb_bounce(orig_addr, tlb_addr,

  				       size, DMA_FROM_DEVICE);

  		else
  			BUG_ON(dir != DMA_TO_DEVICE);

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

  			swiotlb_bounce(orig_addr, tlb_addr,

  				       size, DMA_TO_DEVICE);

  		else
  			BUG_ON(dir != DMA_FROM_DEVICE);

  		break;
  	default:

  		BUG();

  	}

  }

  EXPORT_SYMBOL_GPL(swiotlb_tbl_sync_single);

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

  		       dma_addr_t *dma_handle, gfp_t flags)

  {

  	bool warn = !(flags & __GFP_NOWARN);

  	dma_addr_t dev_addr;

  	void *ret;
  	int order = get_order(size);

  	u64 dma_mask = DMA_BIT_MASK(32);

  
  	if (hwdev && hwdev->coherent_dma_mask)
  		dma_mask = hwdev->coherent_dma_mask;

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

  	if (ret) {
  		dev_addr = swiotlb_virt_to_bus(hwdev, ret);
  		if (dev_addr + size - 1 > dma_mask) {
  			/*
  			 * The allocated memory isn't reachable by the device.
  			 */
  			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 map_single(), which

  		 * will grab memory from the lowest available address range.

  		 */

  		phys_addr_t paddr = map_single(hwdev, 0, size, DMA_FROM_DEVICE,
  					       warn ? 0 : DMA_ATTR_NO_WARN);

  		if (paddr == SWIOTLB_MAP_ERROR)

  			goto err_warn;

  		ret = phys_to_virt(paddr);

  		dev_addr = swiotlb_phys_to_dma(hwdev, paddr);

  		/* Confirm address can be DMA'd by device */
  		if (dev_addr + size - 1 > dma_mask) {
  			printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx
  ",
  			       (unsigned long long)dma_mask,
  			       (unsigned long long)dev_addr);

  			/*
  			 * DMA_TO_DEVICE to avoid memcpy in unmap_single.
  			 * The DMA_ATTR_SKIP_CPU_SYNC is optional.
  			 */

  			swiotlb_tbl_unmap_single(hwdev, paddr,

  						 size, DMA_TO_DEVICE,
  						 DMA_ATTR_SKIP_CPU_SYNC);

  			goto err_warn;

  		}

  	}

  	*dma_handle = dev_addr;

  	memset(ret, 0, size);

  	return ret;

  
  err_warn:

  	if (warn && printk_ratelimit()) {
  		pr_warn("swiotlb: coherent allocation failed for device %s size=%zu
  ",
  			dev_name(hwdev), size);
  		dump_stack();
  	}

  
  	return NULL;

  }

  EXPORT_SYMBOL(swiotlb_alloc_coherent);

  
  void
  swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,

  		      dma_addr_t dev_addr)

  {

  	phys_addr_t paddr = dma_to_phys(hwdev, dev_addr);

  	WARN_ON(irqs_disabled());

  	if (!is_swiotlb_buffer(paddr))
  		free_pages((unsigned long)vaddr, get_order(size));

  	else

  		/*
  		 * DMA_TO_DEVICE to avoid memcpy in swiotlb_tbl_unmap_single.
  		 * DMA_ATTR_SKIP_CPU_SYNC is optional.
  		 */
  		swiotlb_tbl_unmap_single(hwdev, paddr, size, DMA_TO_DEVICE,
  					 DMA_ATTR_SKIP_CPU_SYNC);

  }

  EXPORT_SYMBOL(swiotlb_free_coherent);

  
  static void

  swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
  	     int do_panic)

  {

  	if (swiotlb_force == SWIOTLB_NO_FORCE)
  		return;

  	/*
  	 * 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.
  	 */

  	dev_err_ratelimited(dev, "DMA: Out of SW-IOMMU space for %zu bytes
  ",
  			    size);

  	if (size <= io_tlb_overflow || !do_panic)
  		return;
  
  	if (dir == DMA_BIDIRECTIONAL)
  		panic("DMA: Random memory could be DMA accessed
  ");
  	if (dir == DMA_FROM_DEVICE)
  		panic("DMA: Random memory could be DMA written
  ");
  	if (dir == DMA_TO_DEVICE)
  		panic("DMA: Random memory could be DMA read
  ");

  }
  
  /*
   * 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_page or swiotlb_dma_sync_single is performed.

   */

  dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
  			    unsigned long offset, size_t size,
  			    enum dma_data_direction dir,

  			    unsigned long attrs)

  {

  	phys_addr_t map, phys = page_to_phys(page) + offset;

  	dma_addr_t dev_addr = phys_to_dma(dev, phys);

  	BUG_ON(dir == DMA_NONE);

  	/*

  	 * If the address happens to be in the device's DMA window,

  	 * we can safely return the device addr and not worry about bounce
  	 * buffering it.
  	 */

  	if (dma_capable(dev, dev_addr, size) && swiotlb_force != SWIOTLB_FORCE)

  		return dev_addr;

  	trace_swiotlb_bounced(dev, dev_addr, size, swiotlb_force);

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

  	map = map_single(dev, phys, size, dir, attrs);

  	if (map == SWIOTLB_MAP_ERROR) {

  		swiotlb_full(dev, size, dir, 1);

  		return swiotlb_phys_to_dma(dev, io_tlb_overflow_buffer);

  	}

  	dev_addr = swiotlb_phys_to_dma(dev, map);

  	/* Ensure that the address returned is DMA'ble */

  	if (dma_capable(dev, dev_addr, size))
  		return dev_addr;

  	attrs |= DMA_ATTR_SKIP_CPU_SYNC;
  	swiotlb_tbl_unmap_single(dev, map, size, dir, attrs);

  	return swiotlb_phys_to_dma(dev, io_tlb_overflow_buffer);

  }

  EXPORT_SYMBOL_GPL(swiotlb_map_page);

  
  /*

   * Unmap a single streaming mode DMA translation.  The dma_addr and size must

   * match what was provided for in a previous swiotlb_map_page 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.
   */

  static void unmap_single(struct device *hwdev, dma_addr_t dev_addr,

  			 size_t size, enum dma_data_direction dir,
  			 unsigned long attrs)

  {

  	phys_addr_t paddr = dma_to_phys(hwdev, dev_addr);

  	BUG_ON(dir == DMA_NONE);

  	if (is_swiotlb_buffer(paddr)) {

  		swiotlb_tbl_unmap_single(hwdev, paddr, size, dir, attrs);

  		return;
  	}
  
  	if (dir != DMA_FROM_DEVICE)
  		return;

  	/*
  	 * phys_to_virt doesn't work with hihgmem page but we could
  	 * call dma_mark_clean() with hihgmem page here. However, we
  	 * are fine since dma_mark_clean() is null on POWERPC. We can
  	 * make dma_mark_clean() take a physical address if necessary.
  	 */
  	dma_mark_clean(phys_to_virt(paddr), size);

  }
  
  void swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
  			size_t size, enum dma_data_direction dir,

  			unsigned long attrs)

  {

  	unmap_single(hwdev, dev_addr, size, dir, attrs);

  }

  EXPORT_SYMBOL_GPL(swiotlb_unmap_page);

  /*
   * Make physical memory consistent for a single streaming mode DMA translation
   * after a transfer.
   *

   * If you perform a swiotlb_map_page() 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, enum dma_data_direction dir,
  		    enum dma_sync_target target)

  {

  	phys_addr_t paddr = dma_to_phys(hwdev, dev_addr);

  	BUG_ON(dir == DMA_NONE);

  	if (is_swiotlb_buffer(paddr)) {

  		swiotlb_tbl_sync_single(hwdev, paddr, size, dir, target);

  		return;
  	}
  
  	if (dir != DMA_FROM_DEVICE)
  		return;

  	dma_mark_clean(phys_to_virt(paddr), size);

  }
  
  void

  swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,

  			    size_t size, enum dma_data_direction dir)

  {

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

  }

  EXPORT_SYMBOL(swiotlb_sync_single_for_cpu);

  
  void

  swiotlb_sync_single_for_device(struct device *hwdev, dma_addr_t dev_addr,

  			       size_t size, enum dma_data_direction dir)

  {

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

  }

  EXPORT_SYMBOL(swiotlb_sync_single_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_page

   * 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_page are the

   * same here.
   */
  int

  swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, int nelems,

  		     enum dma_data_direction dir, unsigned long attrs)

  {

  	struct scatterlist *sg;

  	int i;

  	BUG_ON(dir == DMA_NONE);

  	for_each_sg(sgl, sg, nelems, i) {

  		phys_addr_t paddr = sg_phys(sg);

  		dma_addr_t dev_addr = phys_to_dma(hwdev, paddr);

  		if (swiotlb_force == SWIOTLB_FORCE ||

  		    !dma_capable(hwdev, dev_addr, sg->length)) {

  			phys_addr_t map = map_single(hwdev, sg_phys(sg),

  						     sg->length, dir, attrs);

  			if (map == SWIOTLB_MAP_ERROR) {

  				/* Don't panic here, we expect map_sg users
  				   to do proper error handling. */
  				swiotlb_full(hwdev, sg->length, dir, 0);

  				attrs |= DMA_ATTR_SKIP_CPU_SYNC;

  				swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
  						       attrs);

  				sg_dma_len(sgl) = 0;

  				return 0;
  			}

  			sg->dma_address = swiotlb_phys_to_dma(hwdev, map);

  		} else
  			sg->dma_address = dev_addr;

  		sg_dma_len(sg) = sg->length;

  	}
  	return nelems;
  }

  EXPORT_SYMBOL(swiotlb_map_sg_attrs);

  /*
   * Unmap a set of streaming mode DMA translations.  Again, cpu read rules

   * concerning calls here are the same as for swiotlb_unmap_page() above.

   */
  void

  swiotlb_unmap_sg_attrs(struct device *hwdev, struct scatterlist *sgl,

  		       int nelems, enum dma_data_direction dir,
  		       unsigned long attrs)

  {

  	struct scatterlist *sg;

  	int i;

  	BUG_ON(dir == DMA_NONE);

  	for_each_sg(sgl, sg, nelems, i)

  		unmap_single(hwdev, sg->dma_address, sg_dma_len(sg), dir,
  			     attrs);

  }

  EXPORT_SYMBOL(swiotlb_unmap_sg_attrs);

  /*
   * 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 *sgl,

  		int nelems, enum dma_data_direction dir,
  		enum dma_sync_target target)

  {

  	struct scatterlist *sg;

  	int i;

  	for_each_sg(sgl, sg, nelems, i)
  		swiotlb_sync_single(hwdev, sg->dma_address,

  				    sg_dma_len(sg), dir, target);

  }
  
  void

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

  			int nelems, enum dma_data_direction dir)

  {

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

  }

  EXPORT_SYMBOL(swiotlb_sync_sg_for_cpu);

  
  void

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

  			   int nelems, enum dma_data_direction dir)

  {

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

  }

  EXPORT_SYMBOL(swiotlb_sync_sg_for_device);

  
  int

  swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)

  {

  	return (dma_addr == swiotlb_phys_to_dma(hwdev, io_tlb_overflow_buffer));

  }

  EXPORT_SYMBOL(swiotlb_dma_mapping_error);

  
  /*

   * 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 swiotlb_phys_to_dma(hwdev, io_tlb_end - 1) <= mask;

  }

  EXPORT_SYMBOL(swiotlb_dma_supported);