x86: minor cleanup of comments in processor.h

[wrt350n-kernel.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.
 */

#include <linux/cache.h>
#include <linux/dma-mapping.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ctype.h>

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

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

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

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

/*
 * Maximum allowable number of contiguous slabs to map,
 * must be a power of 2.  What is the appropriate value ?
 * The complexity of {map,unmap}_single is linearly dependent on this value.
 */
#define IO_TLB_SEGSIZE  128

/*
 * log of the size of each IO TLB slab.  The number of slabs is command line
 * controllable.
 */
#define IO_TLB_SHIFT 11

#define SLABS_PER_PAGE (1 << (PAGE_SHIFT - IO_TLB_SHIFT))

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

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

int swiotlb_force;

/*
 * Used to do a quick range check in swiotlb_unmap_single and
 * swiotlb_sync_single_*, to see if the memory was in fact allocated by this
 * API.
 */
static char *io_tlb_start, *io_tlb_end;

/*
 * The number of IO TLB blocks (in groups of 64) betweeen io_tlb_start and
 * io_tlb_end.  This is command line adjustable via setup_io_tlb_npages.
 */
static unsigned long io_tlb_nslabs;

/*
 * When the IOMMU overflows we return a fallback buffer. This sets the size.
 */
static unsigned long io_tlb_overflow = 32*1024;

void *io_tlb_overflow_buffer;

/*
 * This is a free list describing the number of free entries available from
 * each index
 */
static unsigned int *io_tlb_list;
static unsigned int io_tlb_index;

/*
 * We need to save away the original address corresponding to a mapped entry
 * for the sync operations.
 */
static unsigned char **io_tlb_orig_addr;

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

static int __init
setup_io_tlb_npages(char *str)
{
        if (isdigit(*str)) {
                io_tlb_nslabs = simple_strtoul(str, &str, 0);
                /* avoid tail segment of size < IO_TLB_SEGSIZE */
                io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
        }
        if (*str == ',')
                ++str;
        if (!strcmp(str, "force"))
                swiotlb_force = 1;
        return 1;
}
__setup("swiotlb=", setup_io_tlb_npages);
/* make io_tlb_overflow tunable too? */

/*
 * Statically reserve bounce buffer space and initialize bounce buffer data
 * structures for the software IO TLB used to implement the DMA API.
 */
void __init
swiotlb_init_with_default_size(size_t default_size)
{
        unsigned long i, bytes;

        if (!io_tlb_nslabs) {
                io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
                io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
        }

        bytes = io_tlb_nslabs << IO_TLB_SHIFT;

        /*
         * Get IO TLB memory from the low pages
         */
        io_tlb_start = alloc_bootmem_low_pages(bytes);
        if (!io_tlb_start)
                panic("Cannot allocate SWIOTLB buffer");
        io_tlb_end = io_tlb_start + bytes;

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

        /*
         * Get the overflow emergency buffer
         */
        io_tlb_overflow_buffer = alloc_bootmem_low(io_tlb_overflow);
        if (!io_tlb_overflow_buffer)
                panic("Cannot allocate SWIOTLB overflow buffer!\n");

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

void __init
swiotlb_init(void)
{
        swiotlb_init_with_default_size(64 * (1<<20));   /* default to 64MB */
}

/*
 * Systems with larger DMA zones (those that don't support ISA) can
 * initialize the swiotlb later using the slab allocator if needed.
 * This should be just like above, but with some error catching.
 */
int
swiotlb_late_init_with_default_size(size_t default_size)
{
        unsigned long i, bytes, req_nslabs = io_tlb_nslabs;
        unsigned int order;

        if (!io_tlb_nslabs) {
                io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
                io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
        }

        /*
         * Get IO TLB memory from the low pages
         */
        order = get_order(io_tlb_nslabs << IO_TLB_SHIFT);
        io_tlb_nslabs = SLABS_PER_PAGE << order;
        bytes = io_tlb_nslabs << IO_TLB_SHIFT;

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

        if (!io_tlb_start)
                goto cleanup1;

        if (order != get_order(bytes)) {
                printk(KERN_WARNING "Warning: only able to allocate %ld MB "
                       "for software IO TLB\n", (PAGE_SIZE << order) >> 20);
                io_tlb_nslabs = SLABS_PER_PAGE << order;
                bytes = io_tlb_nslabs << IO_TLB_SHIFT;
        }
        io_tlb_end = io_tlb_start + bytes;
        memset(io_tlb_start, 0, bytes);

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

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

        io_tlb_orig_addr = (unsigned char **)__get_free_pages(GFP_KERNEL,
                                   get_order(io_tlb_nslabs * sizeof(char *)));
        if (!io_tlb_orig_addr)
                goto cleanup3;

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

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

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

        return 0;

cleanup4:
        free_pages((unsigned long)io_tlb_orig_addr, get_order(io_tlb_nslabs *
                                                              sizeof(char *)));
        io_tlb_orig_addr = NULL;
cleanup3:
        free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
                                                         sizeof(int)));
        io_tlb_list = NULL;
cleanup2:
        io_tlb_end = NULL;
        free_pages((unsigned long)io_tlb_start, order);
        io_tlb_start = NULL;
cleanup1:
        io_tlb_nslabs = req_nslabs;
        return -ENOMEM;
}

static int
address_needs_mapping(struct device *hwdev, dma_addr_t addr)
{
        dma_addr_t mask = 0xffffffff;
        /* If the device has a mask, use it, otherwise default to 32 bits */
        if (hwdev && hwdev->dma_mask)
                mask = *hwdev->dma_mask;
        return (addr & ~mask) != 0;
}

static inline unsigned int is_span_boundary(unsigned int index,
                                            unsigned int nslots,
                                            unsigned long offset_slots,
                                            unsigned long max_slots)
{
        unsigned long offset = (offset_slots + index) & (max_slots - 1);
        return offset + nslots > max_slots;
}

/*
 * Allocates bounce buffer and returns its kernel virtual address.
 */
static void *
map_single(struct device *hwdev, char *buffer, size_t size, int dir)
{
        unsigned long flags;
        char *dma_addr;
        unsigned int nslots, stride, index, wrap;
        int i;
        unsigned long start_dma_addr;
        unsigned long mask;
        unsigned long offset_slots;
        unsigned long max_slots;

        mask = dma_get_seg_boundary(hwdev);
        start_dma_addr = virt_to_bus(io_tlb_start) & mask;

        offset_slots = ALIGN(start_dma_addr, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT;
        max_slots = ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> 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;

                while (is_span_boundary(index, nslots, offset_slots,
                                        max_slots)) {
                        index += stride;
                        if (index >= io_tlb_nslabs)
                                index = 0;
                }
                wrap = index;

                do {
                        /*
                         * If we find a slot that indicates we have 'nslots'
                         * number of contiguous buffers, we allocate the
                         * buffers from that slot and mark the entries as '0'
                         * indicating unavailable.
                         */
                        if (io_tlb_list[index] >= nslots) {
                                int count = 0;

                                for (i = index; i < (int) (index + nslots); i++)
                                        io_tlb_list[i] = 0;
                                for (i = index - 1; (OFFSET(i, IO_TLB_SEGSIZE) != IO_TLB_SEGSIZE -1) && io_tlb_list[i]; i--)
                                        io_tlb_list[i] = ++count;
                                dma_addr = io_tlb_start + (index << IO_TLB_SHIFT);

                                /*
                                 * Update the indices to avoid searching in
                                 * the next round.
                                 */
                                io_tlb_index = ((index + nslots) < io_tlb_nslabs
                                                ? (index + nslots) : 0);

                                goto found;
                        }
                        do {
                                index += stride;
                                if (index >= io_tlb_nslabs)
                                        index = 0;
                        } while (is_span_boundary(index, nslots, offset_slots,
                                                  max_slots));
                } while (index != wrap);

                spin_unlock_irqrestore(&io_tlb_lock, flags);
                return NULL;
        }
  found:
        spin_unlock_irqrestore(&io_tlb_lock, flags);

        /*
         * Save away the mapping from the original address to the DMA address.
         * This is needed when we sync the memory.  Then we sync the buffer if
         * needed.
         */
        for (i = 0; i < nslots; i++)
                io_tlb_orig_addr[index+i] = buffer + (i << IO_TLB_SHIFT);
        if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
                memcpy(dma_addr, buffer, size);

        return dma_addr;
}

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

        /*
         * First, sync the memory before unmapping the entry
         */
        if (buffer && ((dir == DMA_FROM_DEVICE) || (dir == DMA_BIDIRECTIONAL)))
                /*
                 * bounce... copy the data back into the original buffer * and
                 * delete the bounce buffer.
                 */
                memcpy(buffer, dma_addr, size);

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

static void
sync_single(struct device *hwdev, char *dma_addr, size_t size,
            int dir, int target)
{
        int index = (dma_addr - io_tlb_start) >> IO_TLB_SHIFT;
        char *buffer = io_tlb_orig_addr[index];

        buffer += ((unsigned long)dma_addr & ((1 << IO_TLB_SHIFT) - 1));

        switch (target) {
        case SYNC_FOR_CPU:
                if (likely(dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL))
                        memcpy(buffer, dma_addr, size);
                else
                        BUG_ON(dir != DMA_TO_DEVICE);
                break;
        case SYNC_FOR_DEVICE:
                if (likely(dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
                        memcpy(dma_addr, buffer, size);
                else
                        BUG_ON(dir != DMA_FROM_DEVICE);
                break;
        default:
                BUG();
        }
}

void *
swiotlb_alloc_coherent(struct device *hwdev, size_t size,
                       dma_addr_t *dma_handle, gfp_t flags)
{
        dma_addr_t dev_addr;
        void *ret;
        int order = get_order(size);

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

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

                ret = bus_to_virt(handle);
        }

        memset(ret, 0, size);
        dev_addr = virt_to_bus(ret);

        /* Confirm address can be DMA'd by device */
        if (address_needs_mapping(hwdev, dev_addr)) {
                printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
                       (unsigned long long)*hwdev->dma_mask,
                       (unsigned long long)dev_addr);
                panic("swiotlb_alloc_coherent: allocated memory is out of "
                      "range for device");
        }
        *dma_handle = dev_addr;
        return ret;
}

void
swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
                      dma_addr_t dma_handle)
{
        WARN_ON(irqs_disabled());
        if (!(vaddr >= (void *)io_tlb_start
                    && vaddr < (void *)io_tlb_end))
                free_pages((unsigned long) vaddr, get_order(size));
        else
                /* DMA_TO_DEVICE to avoid memcpy in unmap_single */
                swiotlb_unmap_single (hwdev, dma_handle, size, DMA_TO_DEVICE);
}

static void
swiotlb_full(struct device *dev, size_t size, int dir, int do_panic)
{
        /*
         * Ran out of IOMMU space for this operation. This is very bad.
         * Unfortunately the drivers cannot handle this operation properly.
         * unless they check for dma_mapping_error (most don't)
         * When the mapping is small enough return a static buffer to limit
         * the damage, or panic when the transfer is too big.
         */
        printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
               "device %s\n", size, dev ? dev->bus_id : "?");

        if (size > io_tlb_overflow && do_panic) {
                if (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)
                        panic("DMA: Memory would be corrupted\n");
                if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
                        panic("DMA: Random memory would be DMAed\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_single or swiotlb_dma_sync_single is performed.
 */
dma_addr_t
swiotlb_map_single(struct device *hwdev, void *ptr, size_t size, int dir)
{
        dma_addr_t dev_addr = virt_to_bus(ptr);
        void *map;

        BUG_ON(dir == DMA_NONE);
        /*
         * If the pointer passed in happens to be in the device's DMA window,
         * we can safely return the device addr and not worry about bounce
         * buffering it.
         */
        if (!address_needs_mapping(hwdev, dev_addr) && !swiotlb_force)
                return dev_addr;

        /*
         * Oh well, have to allocate and map a bounce buffer.
         */
        map = map_single(hwdev, ptr, size, dir);
        if (!map) {
                swiotlb_full(hwdev, size, dir, 1);
                map = io_tlb_overflow_buffer;
        }

        dev_addr = virt_to_bus(map);

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

        return dev_addr;
}

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

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

/*
 * Make physical memory consistent for a single streaming mode DMA translation
 * after a transfer.
 *
 * If you perform a swiotlb_map_single() but wish to interrogate the buffer
 * using the cpu, yet do not wish to teardown the dma mapping, you must
 * call this function before doing so.  At the next point you give the dma
 * address back to the card, you must first perform a
 * swiotlb_dma_sync_for_device, and then the device again owns the buffer
 */
static void
swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
                    size_t size, int dir, int target)
{
        char *dma_addr = bus_to_virt(dev_addr);

        BUG_ON(dir == DMA_NONE);
        if (dma_addr >= io_tlb_start && dma_addr < io_tlb_end)
                sync_single(hwdev, dma_addr, size, dir, target);
        else if (dir == DMA_FROM_DEVICE)
                dma_mark_clean(dma_addr, size);
}

void
swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,
                            size_t size, int dir)
{
        swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_CPU);
}

void
swiotlb_sync_single_for_device(struct device *hwdev, dma_addr_t dev_addr,
                               size_t size, int dir)
{
        swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_DEVICE);
}

/*
 * Same as above, but for a sub-range of the mapping.
 */
static void
swiotlb_sync_single_range(struct device *hwdev, dma_addr_t dev_addr,
                          unsigned long offset, size_t size,
                          int dir, int target)
{
        char *dma_addr = bus_to_virt(dev_addr) + offset;

        BUG_ON(dir == DMA_NONE);
        if (dma_addr >= io_tlb_start && dma_addr < io_tlb_end)
                sync_single(hwdev, dma_addr, size, dir, target);
        else if (dir == DMA_FROM_DEVICE)
                dma_mark_clean(dma_addr, size);
}

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

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

/*
 * Map a set of buffers described by scatterlist in streaming mode for DMA.
 * This is the scatter-gather version of the above swiotlb_map_single
 * interface.  Here the scatter gather list elements are each tagged with the
 * appropriate dma address and length.  They are obtained via
 * sg_dma_{address,length}(SG).
 *
 * NOTE: An implementation may be able to use a smaller number of
 *       DMA address/length pairs than there are SG table elements.
 *       (for example via virtual mapping capabilities)
 *       The routine returns the number of addr/length pairs actually
 *       used, at most nents.
 *
 * Device ownership issues as mentioned above for swiotlb_map_single are the
 * same here.
 */
int
swiotlb_map_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
               int dir)
{
        struct scatterlist *sg;
        void *addr;
        dma_addr_t dev_addr;
        int i;

        BUG_ON(dir == DMA_NONE);

        for_each_sg(sgl, sg, nelems, i) {
                addr = SG_ENT_VIRT_ADDRESS(sg);
                dev_addr = virt_to_bus(addr);
                if (swiotlb_force || address_needs_mapping(hwdev, dev_addr)) {
                        void *map = map_single(hwdev, addr, sg->length, dir);
                        if (!map) {
                                /* Don't panic here, we expect map_sg users
                                   to do proper error handling. */
                                swiotlb_full(hwdev, sg->length, dir, 0);
                                swiotlb_unmap_sg(hwdev, sgl, i, dir);
                                sgl[0].dma_length = 0;
                                return 0;
                        }
                        sg->dma_address = virt_to_bus(map);
                } else
                        sg->dma_address = dev_addr;
                sg->dma_length = sg->length;
        }
        return nelems;
}

/*
 * Unmap a set of streaming mode DMA translations.  Again, cpu read rules
 * concerning calls here are the same as for swiotlb_unmap_single() above.
 */
void
swiotlb_unmap_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
                 int dir)
{
        struct scatterlist *sg;
        int i;

        BUG_ON(dir == DMA_NONE);

        for_each_sg(sgl, sg, nelems, i) {
                if (sg->dma_address != SG_ENT_PHYS_ADDRESS(sg))
                        unmap_single(hwdev, bus_to_virt(sg->dma_address),
                                     sg->dma_length, dir);
                else if (dir == DMA_FROM_DEVICE)
                        dma_mark_clean(SG_ENT_VIRT_ADDRESS(sg), sg->dma_length);
        }
}

/*
 * Make physical memory consistent for a set of streaming mode DMA translations
 * after a transfer.
 *
 * The same as swiotlb_sync_single_* but for a scatter-gather list, same rules
 * and usage.
 */
static void
swiotlb_sync_sg(struct device *hwdev, struct scatterlist *sgl,
                int nelems, int dir, int target)
{
        struct scatterlist *sg;
        int i;

        BUG_ON(dir == DMA_NONE);

        for_each_sg(sgl, sg, nelems, i) {
                if (sg->dma_address != SG_ENT_PHYS_ADDRESS(sg))
                        sync_single(hwdev, bus_to_virt(sg->dma_address),
                                    sg->dma_length, dir, target);
                else if (dir == DMA_FROM_DEVICE)
                        dma_mark_clean(SG_ENT_VIRT_ADDRESS(sg), sg->dma_length);
        }
}

void
swiotlb_sync_sg_for_cpu(struct device *hwdev, struct scatterlist *sg,
                        int nelems, int dir)
{
        swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_CPU);
}

void
swiotlb_sync_sg_for_device(struct device *hwdev, struct scatterlist *sg,
                           int nelems, int dir)
{
        swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_DEVICE);
}

int
swiotlb_dma_mapping_error(dma_addr_t dma_addr)
{
        return (dma_addr == virt_to_bus(io_tlb_overflow_buffer));
}

/*
 * Return whether the given device DMA address mask can be supported
 * properly.  For example, if your device can only drive the low 24-bits
 * during bus mastering, then you would pass 0x00ffffff as the mask to
 * this function.
 */
int
swiotlb_dma_supported(struct device *hwdev, u64 mask)
{
        return virt_to_bus(io_tlb_end - 1) <= mask;
}

EXPORT_SYMBOL(swiotlb_map_single);
EXPORT_SYMBOL(swiotlb_unmap_single);
EXPORT_SYMBOL(swiotlb_map_sg);
EXPORT_SYMBOL(swiotlb_unmap_sg);
EXPORT_SYMBOL(swiotlb_sync_single_for_cpu);
EXPORT_SYMBOL(swiotlb_sync_single_for_device);
EXPORT_SYMBOL_GPL(swiotlb_sync_single_range_for_cpu);
EXPORT_SYMBOL_GPL(swiotlb_sync_single_range_for_device);
EXPORT_SYMBOL(swiotlb_sync_sg_for_cpu);
EXPORT_SYMBOL(swiotlb_sync_sg_for_device);
EXPORT_SYMBOL(swiotlb_dma_mapping_error);
EXPORT_SYMBOL(swiotlb_alloc_coherent);
EXPORT_SYMBOL(swiotlb_free_coherent);
EXPORT_SYMBOL(swiotlb_dma_supported);