Merge branch 'x86-build-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-2.6.git] / lib / swiotlb.c

/*
 * 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 <asm/io.h>
#include <asm/dma.h>
#include <asm/scatterlist.h>

#include <linux/init.h>
#include <linux/bootmem.h>
#include <linux/iommu-helper.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)

int 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.
 */
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 = 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 = alloc_bootmem_low_pages_nopanic(
                                                PAGE_ALIGN(io_tlb_overflow));
        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 = alloc_bootmem_pages(PAGE_ALIGN(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_pages(PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));

        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 = alloc_bootmem_low_pages_nopanic(PAGE_ALIGN(bytes));
        if (vstart && !swiotlb_init_with_tbl(vstart, io_tlb_nslabs, verbose))
                return;

        if (io_tlb_start)
                free_bootmem(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;

        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 = (phys_addr_t *)
                __get_free_pages(GFP_KERNEL,
                                 get_order(io_tlb_nslabs *
                                           sizeof(phys_addr_t)));
        if (!io_tlb_orig_addr)
                goto cleanup4;

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

        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 {
                free_bootmem_late(io_tlb_overflow_buffer,
                                  PAGE_ALIGN(io_tlb_overflow));
                free_bootmem_late(__pa(io_tlb_orig_addr),
                                  PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
                free_bootmem_late(__pa(io_tlb_list),
                                  PAGE_ALIGN(io_tlb_nslabs * sizeof(int)));
                free_bootmem_late(io_tlb_start,
                                  PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));
        }
        io_tlb_nslabs = 0;
}

static 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 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);
        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.
 */

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 = 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 && ((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;
                /*
                 * 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];

        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)
                        return NULL;

                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);
                        return NULL;
                }
        }

        *dma_handle = dev_addr;
        memset(ret, 0, size);

        return ret;
}
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)
{
        /*
         * 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,
                            struct dma_attrs *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)
                return dev_addr;

        /* 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,
                        struct dma_attrs *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, struct dma_attrs *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 ||
                    !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, NULL);
}
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, struct dma_attrs *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, NULL);
}
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);