text: #include <linux/dma-mapping.h>
  #include <linux/dma-debug.h>
  #include <linux/dmar.h>
  #include <linux/export.h>
  #include <linux/bootmem.h>
  #include <linux/gfp.h>
  #include <linux/pci.h>
  #include <linux/kmemleak.h>
  
  #include <asm/proto.h>
  #include <asm/dma.h>
  #include <asm/iommu.h>
  #include <asm/gart.h>
  #include <asm/calgary.h>
  #include <asm/x86_init.h>
  #include <asm/iommu_table.h>
  
  static int forbid_dac __read_mostly;
  
  struct dma_map_ops *dma_ops = &nommu_dma_ops;
  EXPORT_SYMBOL(dma_ops);
  
  static int iommu_sac_force __read_mostly;
  
  #ifdef CONFIG_IOMMU_DEBUG
  int panic_on_overflow __read_mostly = 1;
  int force_iommu __read_mostly = 1;
  #else
  int panic_on_overflow __read_mostly = 0;
  int force_iommu __read_mostly = 0;
  #endif
  
  int iommu_merge __read_mostly = 0;
  
  int no_iommu __read_mostly;
  /* Set this to 1 if there is a HW IOMMU in the system */
  int iommu_detected __read_mostly = 0;
  
  /*
   * This variable becomes 1 if iommu=pt is passed on the kernel command line.
   * If this variable is 1, IOMMU implementations do no DMA translation for
   * devices and allow every device to access to whole physical memory. This is
   * useful if a user wants to use an IOMMU only for KVM device assignment to
   * guests and not for driver dma translation.
   */
  int iommu_pass_through __read_mostly;
  
  extern struct iommu_table_entry __iommu_table[], __iommu_table_end[];
  
  /* Dummy device used for NULL arguments (normally ISA). */
  struct device x86_dma_fallback_dev = {
  	.init_name = "fallback device",
  	.coherent_dma_mask = ISA_DMA_BIT_MASK,
  	.dma_mask = &x86_dma_fallback_dev.coherent_dma_mask,
  };
  EXPORT_SYMBOL(x86_dma_fallback_dev);
  
  /* Number of entries preallocated for DMA-API debugging */
  #define PREALLOC_DMA_DEBUG_ENTRIES       65536
  
  void __init pci_iommu_alloc(void)
  {
  	struct iommu_table_entry *p;
  
  	sort_iommu_table(__iommu_table, __iommu_table_end);
  	check_iommu_entries(__iommu_table, __iommu_table_end);
  
  	for (p = __iommu_table; p < __iommu_table_end; p++) {
  		if (p && p->detect && p->detect() > 0) {
  			p->flags |= IOMMU_DETECTED;
  			if (p->early_init)
  				p->early_init();
  			if (p->flags & IOMMU_FINISH_IF_DETECTED)
  				break;
  		}
  	}
  }
  void *dma_generic_alloc_coherent(struct device *dev, size_t size,
  				 dma_addr_t *dma_addr, gfp_t flag,
  				 struct dma_attrs *attrs)
  {
  	unsigned long dma_mask;
  	struct page *page;
  	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
  	dma_addr_t addr;
  
  	dma_mask = dma_alloc_coherent_mask(dev, flag);
  
  	flag &= ~__GFP_ZERO;
  again:
  	page = NULL;
  	/* CMA can be used only in the context which permits sleeping */
  	if (flag & __GFP_WAIT) {
  		page = dma_alloc_from_contiguous(dev, count, get_order(size));
  		if (page && page_to_phys(page) + size > dma_mask) {
  			dma_release_from_contiguous(dev, page, count);
  			page = NULL;
  		}
  	}
  	/* fallback */
  	if (!page)
  		page = alloc_pages_node(dev_to_node(dev), flag, get_order(size));
  	if (!page)
  		return NULL;
  
  	addr = page_to_phys(page);
  	if (addr + size > dma_mask) {
  		__free_pages(page, get_order(size));
  
  		if (dma_mask < DMA_BIT_MASK(32) && !(flag & GFP_DMA)) {
  			flag = (flag & ~GFP_DMA32) | GFP_DMA;
  			goto again;
  		}
  
  		return NULL;
  	}
  	memset(page_address(page), 0, size);
  	*dma_addr = addr;
  	return page_address(page);
  }
  
  void dma_generic_free_coherent(struct device *dev, size_t size, void *vaddr,
  			       dma_addr_t dma_addr, struct dma_attrs *attrs)
  {
  	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
  	struct page *page = virt_to_page(vaddr);
  
  	if (!dma_release_from_contiguous(dev, page, count))
  		free_pages((unsigned long)vaddr, get_order(size));
  }
  
  bool arch_dma_alloc_attrs(struct device **dev, gfp_t *gfp)
  {
  	if (!*dev)
  		*dev = &x86_dma_fallback_dev;
  
  	*gfp &= ~(__GFP_DMA | __GFP_HIGHMEM | __GFP_DMA32);
  	*gfp = dma_alloc_coherent_gfp_flags(*dev, *gfp);
  
  	if (!is_device_dma_capable(*dev))
  		return false;
  	return true;
  
  }
  EXPORT_SYMBOL(arch_dma_alloc_attrs);
  
  /*
   * See <Documentation/x86/x86_64/boot-options.txt> for the iommu kernel
   * parameter documentation.
   */
  static __init int iommu_setup(char *p)
  {
  	iommu_merge = 1;
  
  	if (!p)
  		return -EINVAL;
  
  	while (*p) {
  		if (!strncmp(p, "off", 3))
  			no_iommu = 1;
  		/* gart_parse_options has more force support */
  		if (!strncmp(p, "force", 5))
  			force_iommu = 1;
  		if (!strncmp(p, "noforce", 7)) {
  			iommu_merge = 0;
  			force_iommu = 0;
  		}
  
  		if (!strncmp(p, "biomerge", 8)) {
  			iommu_merge = 1;
  			force_iommu = 1;
  		}
  		if (!strncmp(p, "panic", 5))
  			panic_on_overflow = 1;
  		if (!strncmp(p, "nopanic", 7))
  			panic_on_overflow = 0;
  		if (!strncmp(p, "merge", 5)) {
  			iommu_merge = 1;
  			force_iommu = 1;
  		}
  		if (!strncmp(p, "nomerge", 7))
  			iommu_merge = 0;
  		if (!strncmp(p, "forcesac", 8))
  			iommu_sac_force = 1;
  		if (!strncmp(p, "allowdac", 8))
  			forbid_dac = 0;
  		if (!strncmp(p, "nodac", 5))
  			forbid_dac = 1;
  		if (!strncmp(p, "usedac", 6)) {
  			forbid_dac = -1;
  			return 1;
  		}
  #ifdef CONFIG_SWIOTLB
  		if (!strncmp(p, "soft", 4))
  			swiotlb = 1;
  #endif
  		if (!strncmp(p, "pt", 2))
  			iommu_pass_through = 1;
  
  		gart_parse_options(p);
  
  #ifdef CONFIG_CALGARY_IOMMU
  		if (!strncmp(p, "calgary", 7))
  			use_calgary = 1;
  #endif /* CONFIG_CALGARY_IOMMU */
  
  		p += strcspn(p, ",");
  		if (*p == ',')
  			++p;
  	}
  	return 0;
  }
  early_param("iommu", iommu_setup);
  
  int dma_supported(struct device *dev, u64 mask)
  {
  	struct dma_map_ops *ops = get_dma_ops(dev);
  
  #ifdef CONFIG_PCI
  	if (mask > 0xffffffff && forbid_dac > 0) {
  		dev_info(dev, "PCI: Disallowing DAC for device\n");
  		return 0;
  	}
  #endif
  
  	if (ops->dma_supported)
  		return ops->dma_supported(dev, mask);
  
  	/* Copied from i386. Doesn't make much sense, because it will
  	   only work for pci_alloc_coherent.
  	   The caller just has to use GFP_DMA in this case. */
  	if (mask < DMA_BIT_MASK(24))
  		return 0;
  
  	/* Tell the device to use SAC when IOMMU force is on.  This
  	   allows the driver to use cheaper accesses in some cases.
  
  	   Problem with this is that if we overflow the IOMMU area and
  	   return DAC as fallback address the device may not handle it
  	   correctly.
  
  	   As a special case some controllers have a 39bit address
  	   mode that is as efficient as 32bit (aic79xx). Don't force
  	   SAC for these.  Assume all masks <= 40 bits are of this
  	   type. Normally this doesn't make any difference, but gives
  	   more gentle handling of IOMMU overflow. */
  	if (iommu_sac_force && (mask >= DMA_BIT_MASK(40))) {
  		dev_info(dev, "Force SAC with mask %Lx\n", mask);
  		return 0;
  	}
  
  	return 1;
  }
  EXPORT_SYMBOL(dma_supported);
  
  static int __init pci_iommu_init(void)
  {
  	struct iommu_table_entry *p;
  	dma_debug_init(PREALLOC_DMA_DEBUG_ENTRIES);
  
  #ifdef CONFIG_PCI
  	dma_debug_add_bus(&pci_bus_type);
  #endif
  	x86_init.iommu.iommu_init();
  
  	for (p = __iommu_table; p < __iommu_table_end; p++) {
  		if (p && (p->flags & IOMMU_DETECTED) && p->late_init)
  			p->late_init();
  	}
  
  	return 0;
  }
  /* Must execute after PCI subsystem */
  rootfs_initcall(pci_iommu_init);
  
  #ifdef CONFIG_PCI
  /* Many VIA bridges seem to corrupt data for DAC. Disable it here */
  
  static void via_no_dac(struct pci_dev *dev)
  {
  	if (forbid_dac == 0) {
  		dev_info(&dev->dev, "disabling DAC on VIA PCI bridge\n");
  		forbid_dac = 1;
  	}
  }
  DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_VIA, PCI_ANY_ID,
  				PCI_CLASS_BRIDGE_PCI, 8, via_no_dac);
  #endif
  