text: /*
   * 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 <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;
  
  /*
   * 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);
  
  /* 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);
  }
  
  /* 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\n");
  		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]\n",
  	       (unsigned long long)io_tlb_start,
  	       (unsigned long long)io_tlb_end,
  	       bytes >> 20, vstart, vend - 1);
  }
  
  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();
  
  	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\n", (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;
  
  	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;
  
  	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;
  
  	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;
  	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;
  }
  
  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 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");
  
  	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 (printk_ratelimit())
  		dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)\n", 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 (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)
  {
  	dma_addr_t start_dma_addr;
  
  	if (swiotlb_force == SWIOTLB_NO_FORCE) {
  		dev_warn_ratelimited(hwdev, "Cannot do DMA to address %pa\n",
  				     &phys);
  		return SWIOTLB_MAP_ERROR;
  	}
  
  	start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
  	return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size, dir);
  }
  
  /*
   * 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 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 &&
  	    ((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)
  {
  	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);
  		if (paddr == SWIOTLB_MAP_ERROR)
  			goto err_warn;
  
  		ret = phys_to_virt(paddr);
  		dev_addr = 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\n",
  			       (unsigned long long)dma_mask,
  			       (unsigned long long)dev_addr);
  
  			/* DMA_TO_DEVICE to avoid memcpy in unmap_single */
  			swiotlb_tbl_unmap_single(hwdev, paddr,
  						 size, DMA_TO_DEVICE);
  			goto err_warn;
  		}
  	}
  
  	*dma_handle = dev_addr;
  	memset(ret, 0, size);
  
  	return ret;
  
  err_warn:
  	pr_warn("swiotlb: coherent allocation failed for device %s size=%zu\n",
  		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 */
  		swiotlb_tbl_unmap_single(hwdev, paddr, size, DMA_TO_DEVICE);
  }
  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.
  	 */
  	printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
  	       "device %s\n", size, dev ? dev_name(dev) : "?");
  
  	if (size <= io_tlb_overflow || !do_panic)
  		return;
  
  	if (dir == DMA_BIDIRECTIONAL)
  		panic("DMA: Random memory could be DMA accessed\n");
  	if (dir == DMA_FROM_DEVICE)
  		panic("DMA: Random memory could be DMA written\n");
  	if (dir == DMA_TO_DEVICE)
  		panic("DMA: Random memory could be DMA read\n");
  }
  
  /*
   * 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);
  	if (map == SWIOTLB_MAP_ERROR) {
  		swiotlb_full(dev, size, dir, 1);
  		return phys_to_dma(dev, io_tlb_overflow_buffer);
  	}
  
  	dev_addr = phys_to_dma(dev, map);
  
  	/* Ensure that the address returned is DMA'ble */
  	if (!dma_capable(dev, dev_addr, size)) {
  		swiotlb_tbl_unmap_single(dev, map, size, dir);
  		return phys_to_dma(dev, io_tlb_overflow_buffer);
  	}
  
  	return dev_addr;
  }
  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)
  {
  	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);
  		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);
  }
  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);
  			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);
  				swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
  						       attrs);
  				sg_dma_len(sgl) = 0;
  				return 0;
  			}
  			sg->dma_address = 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);
  
  int
  swiotlb_map_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
  	       enum dma_data_direction dir)
  {
  	return swiotlb_map_sg_attrs(hwdev, sgl, nelems, dir, 0);
  }
  EXPORT_SYMBOL(swiotlb_map_sg);
  
  /*
   * 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);
  
  }
  EXPORT_SYMBOL(swiotlb_unmap_sg_attrs);
  
  void
  swiotlb_unmap_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
  		 enum dma_data_direction dir)
  {
  	return swiotlb_unmap_sg_attrs(hwdev, sgl, nelems, dir, 0);
  }
  EXPORT_SYMBOL(swiotlb_unmap_sg);
  
  /*
   * 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 == 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 phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
  }
  EXPORT_SYMBOL(swiotlb_dma_supported);
  