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

[mirror_ubuntu-artful-kernel.git] / lib / dma-debug.c

/*
 * Copyright (C) 2008 Advanced Micro Devices, Inc.
 *
 * Author: Joerg Roedel <joerg.roedel@amd.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 */

#include <linux/scatterlist.h>
#include <linux/dma-mapping.h>
#include <linux/stacktrace.h>
#include <linux/dma-debug.h>
#include <linux/spinlock.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/export.h>
#include <linux/device.h>
#include <linux/types.h>
#include <linux/sched.h>
#include <linux/ctype.h>
#include <linux/list.h>
#include <linux/slab.h>

#include <asm/sections.h>

#define HASH_SIZE       1024ULL
#define HASH_FN_SHIFT   13
#define HASH_FN_MASK    (HASH_SIZE - 1)

enum {
        dma_debug_single,
        dma_debug_page,
        dma_debug_sg,
        dma_debug_coherent,
};

enum map_err_types {
        MAP_ERR_CHECK_NOT_APPLICABLE,
        MAP_ERR_NOT_CHECKED,
        MAP_ERR_CHECKED,
};

#define DMA_DEBUG_STACKTRACE_ENTRIES 5

/**
 * struct dma_debug_entry - track a dma_map* or dma_alloc_coherent mapping
 * @list: node on pre-allocated free_entries list
 * @dev: 'dev' argument to dma_map_{page|single|sg} or dma_alloc_coherent
 * @type: single, page, sg, coherent
 * @pfn: page frame of the start address
 * @offset: offset of mapping relative to pfn
 * @size: length of the mapping
 * @direction: enum dma_data_direction
 * @sg_call_ents: 'nents' from dma_map_sg
 * @sg_mapped_ents: 'mapped_ents' from dma_map_sg
 * @map_err_type: track whether dma_mapping_error() was checked
 * @stacktrace: support backtraces when a violation is detected
 */
struct dma_debug_entry {
        struct list_head list;
        struct device    *dev;
        int              type;
        unsigned long    pfn;
        size_t           offset;
        u64              dev_addr;
        u64              size;
        int              direction;
        int              sg_call_ents;
        int              sg_mapped_ents;
        enum map_err_types  map_err_type;
#ifdef CONFIG_STACKTRACE
        struct           stack_trace stacktrace;
        unsigned long    st_entries[DMA_DEBUG_STACKTRACE_ENTRIES];
#endif
};

typedef bool (*match_fn)(struct dma_debug_entry *, struct dma_debug_entry *);

struct hash_bucket {
        struct list_head list;
        spinlock_t lock;
} ____cacheline_aligned_in_smp;

/* Hash list to save the allocated dma addresses */
static struct hash_bucket dma_entry_hash[HASH_SIZE];
/* List of pre-allocated dma_debug_entry's */
static LIST_HEAD(free_entries);
/* Lock for the list above */
static DEFINE_SPINLOCK(free_entries_lock);

/* Global disable flag - will be set in case of an error */
static u32 global_disable __read_mostly;

/* Early initialization disable flag, set at the end of dma_debug_init */
static bool dma_debug_initialized __read_mostly;

static inline bool dma_debug_disabled(void)
{
        return global_disable || !dma_debug_initialized;
}

/* Global error count */
static u32 error_count;

/* Global error show enable*/
static u32 show_all_errors __read_mostly;
/* Number of errors to show */
static u32 show_num_errors = 1;

static u32 num_free_entries;
static u32 min_free_entries;
static u32 nr_total_entries;

/* number of preallocated entries requested by kernel cmdline */
static u32 req_entries;

/* debugfs dentry's for the stuff above */
static struct dentry *dma_debug_dent        __read_mostly;
static struct dentry *global_disable_dent   __read_mostly;
static struct dentry *error_count_dent      __read_mostly;
static struct dentry *show_all_errors_dent  __read_mostly;
static struct dentry *show_num_errors_dent  __read_mostly;
static struct dentry *num_free_entries_dent __read_mostly;
static struct dentry *min_free_entries_dent __read_mostly;
static struct dentry *filter_dent           __read_mostly;

/* per-driver filter related state */

#define NAME_MAX_LEN    64

static char                  current_driver_name[NAME_MAX_LEN] __read_mostly;
static struct device_driver *current_driver                    __read_mostly;

static DEFINE_RWLOCK(driver_name_lock);

static const char *const maperr2str[] = {
        [MAP_ERR_CHECK_NOT_APPLICABLE] = "dma map error check not applicable",
        [MAP_ERR_NOT_CHECKED] = "dma map error not checked",
        [MAP_ERR_CHECKED] = "dma map error checked",
};

static const char *type2name[4] = { "single", "page",
                                    "scather-gather", "coherent" };

static const char *dir2name[4] = { "DMA_BIDIRECTIONAL", "DMA_TO_DEVICE",
                                   "DMA_FROM_DEVICE", "DMA_NONE" };

/*
 * The access to some variables in this macro is racy. We can't use atomic_t
 * here because all these variables are exported to debugfs. Some of them even
 * writeable. This is also the reason why a lock won't help much. But anyway,
 * the races are no big deal. Here is why:
 *
 *   error_count: the addition is racy, but the worst thing that can happen is
 *                that we don't count some errors
 *   show_num_errors: the subtraction is racy. Also no big deal because in
 *                    worst case this will result in one warning more in the
 *                    system log than the user configured. This variable is
 *                    writeable via debugfs.
 */
static inline void dump_entry_trace(struct dma_debug_entry *entry)
{
#ifdef CONFIG_STACKTRACE
        if (entry) {
                pr_warning("Mapped at:\n");
                print_stack_trace(&entry->stacktrace, 0);
        }
#endif
}

static bool driver_filter(struct device *dev)
{
        struct device_driver *drv;
        unsigned long flags;
        bool ret;

        /* driver filter off */
        if (likely(!current_driver_name[0]))
                return true;

        /* driver filter on and initialized */
        if (current_driver && dev && dev->driver == current_driver)
                return true;

        /* driver filter on, but we can't filter on a NULL device... */
        if (!dev)
                return false;

        if (current_driver || !current_driver_name[0])
                return false;

        /* driver filter on but not yet initialized */
        drv = dev->driver;
        if (!drv)
                return false;

        /* lock to protect against change of current_driver_name */
        read_lock_irqsave(&driver_name_lock, flags);

        ret = false;
        if (drv->name &&
            strncmp(current_driver_name, drv->name, NAME_MAX_LEN - 1) == 0) {
                current_driver = drv;
                ret = true;
        }

        read_unlock_irqrestore(&driver_name_lock, flags);

        return ret;
}

#define err_printk(dev, entry, format, arg...) do {                     \
                error_count += 1;                                       \
                if (driver_filter(dev) &&                               \
                    (show_all_errors || show_num_errors > 0)) {         \
                        WARN(1, "%s %s: " format,                       \
                             dev ? dev_driver_string(dev) : "NULL",     \
                             dev ? dev_name(dev) : "NULL", ## arg);     \
                        dump_entry_trace(entry);                        \
                }                                                       \
                if (!show_all_errors && show_num_errors > 0)            \
                        show_num_errors -= 1;                           \
        } while (0);

/*
 * Hash related functions
 *
 * Every DMA-API request is saved into a struct dma_debug_entry. To
 * have quick access to these structs they are stored into a hash.
 */
static int hash_fn(struct dma_debug_entry *entry)
{
        /*
         * Hash function is based on the dma address.
         * We use bits 20-27 here as the index into the hash
         */
        return (entry->dev_addr >> HASH_FN_SHIFT) & HASH_FN_MASK;
}

/*
 * Request exclusive access to a hash bucket for a given dma_debug_entry.
 */
static struct hash_bucket *get_hash_bucket(struct dma_debug_entry *entry,
                                           unsigned long *flags)
{
        int idx = hash_fn(entry);
        unsigned long __flags;

        spin_lock_irqsave(&dma_entry_hash[idx].lock, __flags);
        *flags = __flags;
        return &dma_entry_hash[idx];
}

/*
 * Give up exclusive access to the hash bucket
 */
static void put_hash_bucket(struct hash_bucket *bucket,
                            unsigned long *flags)
{
        unsigned long __flags = *flags;

        spin_unlock_irqrestore(&bucket->lock, __flags);
}

static bool exact_match(struct dma_debug_entry *a, struct dma_debug_entry *b)
{
        return ((a->dev_addr == b->dev_addr) &&
                (a->dev == b->dev)) ? true : false;
}

static bool containing_match(struct dma_debug_entry *a,
                             struct dma_debug_entry *b)
{
        if (a->dev != b->dev)
                return false;

        if ((b->dev_addr <= a->dev_addr) &&
            ((b->dev_addr + b->size) >= (a->dev_addr + a->size)))
                return true;

        return false;
}

/*
 * Search a given entry in the hash bucket list
 */
static struct dma_debug_entry *__hash_bucket_find(struct hash_bucket *bucket,
                                                  struct dma_debug_entry *ref,
                                                  match_fn match)
{
        struct dma_debug_entry *entry, *ret = NULL;
        int matches = 0, match_lvl, last_lvl = -1;

        list_for_each_entry(entry, &bucket->list, list) {
                if (!match(ref, entry))
                        continue;

                /*
                 * Some drivers map the same physical address multiple
                 * times. Without a hardware IOMMU this results in the
                 * same device addresses being put into the dma-debug
                 * hash multiple times too. This can result in false
                 * positives being reported. Therefore we implement a
                 * best-fit algorithm here which returns the entry from
                 * the hash which fits best to the reference value
                 * instead of the first-fit.
                 */
                matches += 1;
                match_lvl = 0;
                entry->size         == ref->size         ? ++match_lvl : 0;
                entry->type         == ref->type         ? ++match_lvl : 0;
                entry->direction    == ref->direction    ? ++match_lvl : 0;
                entry->sg_call_ents == ref->sg_call_ents ? ++match_lvl : 0;

                if (match_lvl == 4) {
                        /* perfect-fit - return the result */
                        return entry;
                } else if (match_lvl > last_lvl) {
                        /*
                         * We found an entry that fits better then the
                         * previous one or it is the 1st match.
                         */
                        last_lvl = match_lvl;
                        ret      = entry;
                }
        }

        /*
         * If we have multiple matches but no perfect-fit, just return
         * NULL.
         */
        ret = (matches == 1) ? ret : NULL;

        return ret;
}

static struct dma_debug_entry *bucket_find_exact(struct hash_bucket *bucket,
                                                 struct dma_debug_entry *ref)
{
        return __hash_bucket_find(bucket, ref, exact_match);
}

static struct dma_debug_entry *bucket_find_contain(struct hash_bucket **bucket,
                                                   struct dma_debug_entry *ref,
                                                   unsigned long *flags)
{

        unsigned int max_range = dma_get_max_seg_size(ref->dev);
        struct dma_debug_entry *entry, index = *ref;
        unsigned int range = 0;

        while (range <= max_range) {
                entry = __hash_bucket_find(*bucket, &index, containing_match);

                if (entry)
                        return entry;

                /*
                 * Nothing found, go back a hash bucket
                 */
                put_hash_bucket(*bucket, flags);
                range          += (1 << HASH_FN_SHIFT);
                index.dev_addr -= (1 << HASH_FN_SHIFT);
                *bucket = get_hash_bucket(&index, flags);
        }

        return NULL;
}

/*
 * Add an entry to a hash bucket
 */
static void hash_bucket_add(struct hash_bucket *bucket,
                            struct dma_debug_entry *entry)
{
        list_add_tail(&entry->list, &bucket->list);
}

/*
 * Remove entry from a hash bucket list
 */
static void hash_bucket_del(struct dma_debug_entry *entry)
{
        list_del(&entry->list);
}

static unsigned long long phys_addr(struct dma_debug_entry *entry)
{
        return page_to_phys(pfn_to_page(entry->pfn)) + entry->offset;
}

/*
 * Dump mapping entries for debugging purposes
 */
void debug_dma_dump_mappings(struct device *dev)
{
        int idx;

        for (idx = 0; idx < HASH_SIZE; idx++) {
                struct hash_bucket *bucket = &dma_entry_hash[idx];
                struct dma_debug_entry *entry;
                unsigned long flags;

                spin_lock_irqsave(&bucket->lock, flags);

                list_for_each_entry(entry, &bucket->list, list) {
                        if (!dev || dev == entry->dev) {
                                dev_info(entry->dev,
                                         "%s idx %d P=%Lx N=%lx D=%Lx L=%Lx %s %s\n",
                                         type2name[entry->type], idx,
                                         phys_addr(entry), entry->pfn,
                                         entry->dev_addr, entry->size,
                                         dir2name[entry->direction],
                                         maperr2str[entry->map_err_type]);
                        }
                }

                spin_unlock_irqrestore(&bucket->lock, flags);
        }
}
EXPORT_SYMBOL(debug_dma_dump_mappings);

/*
 * For each mapping (initial cacheline in the case of
 * dma_alloc_coherent/dma_map_page, initial cacheline in each page of a
 * scatterlist, or the cacheline specified in dma_map_single) insert
 * into this tree using the cacheline as the key. At
 * dma_unmap_{single|sg|page} or dma_free_coherent delete the entry.  If
 * the entry already exists at insertion time add a tag as a reference
 * count for the overlapping mappings.  For now, the overlap tracking
 * just ensures that 'unmaps' balance 'maps' before marking the
 * cacheline idle, but we should also be flagging overlaps as an API
 * violation.
 *
 * Memory usage is mostly constrained by the maximum number of available
 * dma-debug entries in that we need a free dma_debug_entry before
 * inserting into the tree.  In the case of dma_map_page and
 * dma_alloc_coherent there is only one dma_debug_entry and one
 * dma_active_cacheline entry to track per event.  dma_map_sg(), on the
 * other hand, consumes a single dma_debug_entry, but inserts 'nents'
 * entries into the tree.
 *
 * At any time debug_dma_assert_idle() can be called to trigger a
 * warning if any cachelines in the given page are in the active set.
 */
static RADIX_TREE(dma_active_cacheline, GFP_NOWAIT);
static DEFINE_SPINLOCK(radix_lock);
#define ACTIVE_CACHELINE_MAX_OVERLAP ((1 << RADIX_TREE_MAX_TAGS) - 1)
#define CACHELINE_PER_PAGE_SHIFT (PAGE_SHIFT - L1_CACHE_SHIFT)
#define CACHELINES_PER_PAGE (1 << CACHELINE_PER_PAGE_SHIFT)

static phys_addr_t to_cacheline_number(struct dma_debug_entry *entry)
{
        return (entry->pfn << CACHELINE_PER_PAGE_SHIFT) +
                (entry->offset >> L1_CACHE_SHIFT);
}

static int active_cacheline_read_overlap(phys_addr_t cln)
{
        int overlap = 0, i;

        for (i = RADIX_TREE_MAX_TAGS - 1; i >= 0; i--)
                if (radix_tree_tag_get(&dma_active_cacheline, cln, i))
                        overlap |= 1 << i;
        return overlap;
}

static int active_cacheline_set_overlap(phys_addr_t cln, int overlap)
{
        int i;

        if (overlap > ACTIVE_CACHELINE_MAX_OVERLAP || overlap < 0)
                return overlap;

        for (i = RADIX_TREE_MAX_TAGS - 1; i >= 0; i--)
                if (overlap & 1 << i)
                        radix_tree_tag_set(&dma_active_cacheline, cln, i);
                else
                        radix_tree_tag_clear(&dma_active_cacheline, cln, i);

        return overlap;
}

static void active_cacheline_inc_overlap(phys_addr_t cln)
{
        int overlap = active_cacheline_read_overlap(cln);

        overlap = active_cacheline_set_overlap(cln, ++overlap);

        /* If we overflowed the overlap counter then we're potentially
         * leaking dma-mappings.  Otherwise, if maps and unmaps are
         * balanced then this overflow may cause false negatives in
         * debug_dma_assert_idle() as the cacheline may be marked idle
         * prematurely.
         */
        WARN_ONCE(overlap > ACTIVE_CACHELINE_MAX_OVERLAP,
                  "DMA-API: exceeded %d overlapping mappings of cacheline %pa\n",
                  ACTIVE_CACHELINE_MAX_OVERLAP, &cln);
}

static int active_cacheline_dec_overlap(phys_addr_t cln)
{
        int overlap = active_cacheline_read_overlap(cln);

        return active_cacheline_set_overlap(cln, --overlap);
}

static int active_cacheline_insert(struct dma_debug_entry *entry)
{
        phys_addr_t cln = to_cacheline_number(entry);
        unsigned long flags;
        int rc;

        /* If the device is not writing memory then we don't have any
         * concerns about the cpu consuming stale data.  This mitigates
         * legitimate usages of overlapping mappings.
         */
        if (entry->direction == DMA_TO_DEVICE)
                return 0;

        spin_lock_irqsave(&radix_lock, flags);
        rc = radix_tree_insert(&dma_active_cacheline, cln, entry);
        if (rc == -EEXIST)
                active_cacheline_inc_overlap(cln);
        spin_unlock_irqrestore(&radix_lock, flags);

        return rc;
}

static void active_cacheline_remove(struct dma_debug_entry *entry)
{
        phys_addr_t cln = to_cacheline_number(entry);
        unsigned long flags;

        /* ...mirror the insert case */
        if (entry->direction == DMA_TO_DEVICE)
                return;

        spin_lock_irqsave(&radix_lock, flags);
        /* since we are counting overlaps the final put of the
         * cacheline will occur when the overlap count is 0.
         * active_cacheline_dec_overlap() returns -1 in that case
         */
        if (active_cacheline_dec_overlap(cln) < 0)
                radix_tree_delete(&dma_active_cacheline, cln);
        spin_unlock_irqrestore(&radix_lock, flags);
}

/**
 * debug_dma_assert_idle() - assert that a page is not undergoing dma
 * @page: page to lookup in the dma_active_cacheline tree
 *
 * Place a call to this routine in cases where the cpu touching the page
 * before the dma completes (page is dma_unmapped) will lead to data
 * corruption.
 */
void debug_dma_assert_idle(struct page *page)
{
        static struct dma_debug_entry *ents[CACHELINES_PER_PAGE];
        struct dma_debug_entry *entry = NULL;
        void **results = (void **) &ents;
        unsigned int nents, i;
        unsigned long flags;
        phys_addr_t cln;

        if (!page)
                return;

        cln = (phys_addr_t) page_to_pfn(page) << CACHELINE_PER_PAGE_SHIFT;
        spin_lock_irqsave(&radix_lock, flags);
        nents = radix_tree_gang_lookup(&dma_active_cacheline, results, cln,
                                       CACHELINES_PER_PAGE);
        for (i = 0; i < nents; i++) {
                phys_addr_t ent_cln = to_cacheline_number(ents[i]);

                if (ent_cln == cln) {
                        entry = ents[i];
                        break;
                } else if (ent_cln >= cln + CACHELINES_PER_PAGE)
                        break;
        }
        spin_unlock_irqrestore(&radix_lock, flags);

        if (!entry)
                return;

        cln = to_cacheline_number(entry);
        err_printk(entry->dev, entry,
                   "DMA-API: cpu touching an active dma mapped cacheline [cln=%pa]\n",
                   &cln);
}

/*
 * Wrapper function for adding an entry to the hash.
 * This function takes care of locking itself.
 */
static void add_dma_entry(struct dma_debug_entry *entry)
{
        struct hash_bucket *bucket;
        unsigned long flags;
        int rc;

        bucket = get_hash_bucket(entry, &flags);
        hash_bucket_add(bucket, entry);
        put_hash_bucket(bucket, &flags);

        rc = active_cacheline_insert(entry);
        if (rc == -ENOMEM) {
                pr_err("DMA-API: cacheline tracking ENOMEM, dma-debug disabled\n");
                global_disable = true;
        }

        /* TODO: report -EEXIST errors here as overlapping mappings are
         * not supported by the DMA API
         */
}

static struct dma_debug_entry *__dma_entry_alloc(void)
{
        struct dma_debug_entry *entry;

        entry = list_entry(free_entries.next, struct dma_debug_entry, list);
        list_del(&entry->list);
        memset(entry, 0, sizeof(*entry));

        num_free_entries -= 1;
        if (num_free_entries < min_free_entries)
                min_free_entries = num_free_entries;

        return entry;
}

/* struct dma_entry allocator
 *
 * The next two functions implement the allocator for
 * struct dma_debug_entries.
 */
static struct dma_debug_entry *dma_entry_alloc(void)
{
        struct dma_debug_entry *entry;
        unsigned long flags;

        spin_lock_irqsave(&free_entries_lock, flags);

        if (list_empty(&free_entries)) {
                pr_err("DMA-API: debugging out of memory - disabling\n");
                global_disable = true;
                spin_unlock_irqrestore(&free_entries_lock, flags);
                return NULL;
        }

        entry = __dma_entry_alloc();

        spin_unlock_irqrestore(&free_entries_lock, flags);

#ifdef CONFIG_STACKTRACE
        entry->stacktrace.max_entries = DMA_DEBUG_STACKTRACE_ENTRIES;
        entry->stacktrace.entries = entry->st_entries;
        entry->stacktrace.skip = 2;
        save_stack_trace(&entry->stacktrace);
#endif

        return entry;
}

static void dma_entry_free(struct dma_debug_entry *entry)
{
        unsigned long flags;

        active_cacheline_remove(entry);

        /*
         * add to beginning of the list - this way the entries are
         * more likely cache hot when they are reallocated.
         */
        spin_lock_irqsave(&free_entries_lock, flags);
        list_add(&entry->list, &free_entries);
        num_free_entries += 1;
        spin_unlock_irqrestore(&free_entries_lock, flags);
}

int dma_debug_resize_entries(u32 num_entries)
{
        int i, delta, ret = 0;
        unsigned long flags;
        struct dma_debug_entry *entry;
        LIST_HEAD(tmp);

        spin_lock_irqsave(&free_entries_lock, flags);

        if (nr_total_entries < num_entries) {
                delta = num_entries - nr_total_entries;

                spin_unlock_irqrestore(&free_entries_lock, flags);

                for (i = 0; i < delta; i++) {
                        entry = kzalloc(sizeof(*entry), GFP_KERNEL);
                        if (!entry)
                                break;

                        list_add_tail(&entry->list, &tmp);
                }

                spin_lock_irqsave(&free_entries_lock, flags);

                list_splice(&tmp, &free_entries);
                nr_total_entries += i;
                num_free_entries += i;
        } else {
                delta = nr_total_entries - num_entries;

                for (i = 0; i < delta && !list_empty(&free_entries); i++) {
                        entry = __dma_entry_alloc();
                        kfree(entry);
                }

                nr_total_entries -= i;
        }

        if (nr_total_entries != num_entries)
                ret = 1;

        spin_unlock_irqrestore(&free_entries_lock, flags);

        return ret;
}
EXPORT_SYMBOL(dma_debug_resize_entries);

/*
 * DMA-API debugging init code
 *
 * The init code does two things:
 *   1. Initialize core data structures
 *   2. Preallocate a given number of dma_debug_entry structs
 */

static int prealloc_memory(u32 num_entries)
{
        struct dma_debug_entry *entry, *next_entry;
        int i;

        for (i = 0; i < num_entries; ++i) {
                entry = kzalloc(sizeof(*entry), GFP_KERNEL);
                if (!entry)
                        goto out_err;

                list_add_tail(&entry->list, &free_entries);
        }

        num_free_entries = num_entries;
        min_free_entries = num_entries;

        pr_info("DMA-API: preallocated %d debug entries\n", num_entries);

        return 0;

out_err:

        list_for_each_entry_safe(entry, next_entry, &free_entries, list) {
                list_del(&entry->list);
                kfree(entry);
        }

        return -ENOMEM;
}

static ssize_t filter_read(struct file *file, char __user *user_buf,
                           size_t count, loff_t *ppos)
{
        char buf[NAME_MAX_LEN + 1];
        unsigned long flags;
        int len;

        if (!current_driver_name[0])
                return 0;

        /*
         * We can't copy to userspace directly because current_driver_name can
         * only be read under the driver_name_lock with irqs disabled. So
         * create a temporary copy first.
         */
        read_lock_irqsave(&driver_name_lock, flags);
        len = scnprintf(buf, NAME_MAX_LEN + 1, "%s\n", current_driver_name);
        read_unlock_irqrestore(&driver_name_lock, flags);

        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}

static ssize_t filter_write(struct file *file, const char __user *userbuf,
                            size_t count, loff_t *ppos)
{
        char buf[NAME_MAX_LEN];
        unsigned long flags;
        size_t len;
        int i;

        /*
         * We can't copy from userspace directly. Access to
         * current_driver_name is protected with a write_lock with irqs
         * disabled. Since copy_from_user can fault and may sleep we
         * need to copy to temporary buffer first
         */
        len = min(count, (size_t)(NAME_MAX_LEN - 1));
        if (copy_from_user(buf, userbuf, len))
                return -EFAULT;

        buf[len] = 0;

        write_lock_irqsave(&driver_name_lock, flags);

        /*
         * Now handle the string we got from userspace very carefully.
         * The rules are:
         *         - only use the first token we got
         *         - token delimiter is everything looking like a space
         *           character (' ', '\n', '\t' ...)
         *
         */
        if (!isalnum(buf[0])) {
                /*
                 * If the first character userspace gave us is not
                 * alphanumerical then assume the filter should be
                 * switched off.
                 */
                if (current_driver_name[0])
                        pr_info("DMA-API: switching off dma-debug driver filter\n");
                current_driver_name[0] = 0;
                current_driver = NULL;
                goto out_unlock;
        }

        /*
         * Now parse out the first token and use it as the name for the
         * driver to filter for.
         */
        for (i = 0; i < NAME_MAX_LEN - 1; ++i) {
                current_driver_name[i] = buf[i];
                if (isspace(buf[i]) || buf[i] == ' ' || buf[i] == 0)
                        break;
        }
        current_driver_name[i] = 0;
        current_driver = NULL;

        pr_info("DMA-API: enable driver filter for driver [%s]\n",
                current_driver_name);

out_unlock:
        write_unlock_irqrestore(&driver_name_lock, flags);

        return count;
}

static const struct file_operations filter_fops = {
        .read  = filter_read,
        .write = filter_write,
        .llseek = default_llseek,
};

static int dma_debug_fs_init(void)
{
        dma_debug_dent = debugfs_create_dir("dma-api", NULL);
        if (!dma_debug_dent) {
                pr_err("DMA-API: can not create debugfs directory\n");
                return -ENOMEM;
        }

        global_disable_dent = debugfs_create_bool("disabled", 0444,
                        dma_debug_dent,
                        &global_disable);
        if (!global_disable_dent)
                goto out_err;

        error_count_dent = debugfs_create_u32("error_count", 0444,
                        dma_debug_dent, &error_count);
        if (!error_count_dent)
                goto out_err;

        show_all_errors_dent = debugfs_create_u32("all_errors", 0644,
                        dma_debug_dent,
                        &show_all_errors);
        if (!show_all_errors_dent)
                goto out_err;

        show_num_errors_dent = debugfs_create_u32("num_errors", 0644,
                        dma_debug_dent,
                        &show_num_errors);
        if (!show_num_errors_dent)
                goto out_err;

        num_free_entries_dent = debugfs_create_u32("num_free_entries", 0444,
                        dma_debug_dent,
                        &num_free_entries);
        if (!num_free_entries_dent)
                goto out_err;

        min_free_entries_dent = debugfs_create_u32("min_free_entries", 0444,
                        dma_debug_dent,
                        &min_free_entries);
        if (!min_free_entries_dent)
                goto out_err;

        filter_dent = debugfs_create_file("driver_filter", 0644,
                                          dma_debug_dent, NULL, &filter_fops);
        if (!filter_dent)
                goto out_err;

        return 0;

out_err:
        debugfs_remove_recursive(dma_debug_dent);

        return -ENOMEM;
}

static int device_dma_allocations(struct device *dev, struct dma_debug_entry **out_entry)
{
        struct dma_debug_entry *entry;
        unsigned long flags;
        int count = 0, i;

        local_irq_save(flags);

        for (i = 0; i < HASH_SIZE; ++i) {
                spin_lock(&dma_entry_hash[i].lock);
                list_for_each_entry(entry, &dma_entry_hash[i].list, list) {
                        if (entry->dev == dev) {
                                count += 1;
                                *out_entry = entry;
                        }
                }
                spin_unlock(&dma_entry_hash[i].lock);
        }

        local_irq_restore(flags);

        return count;
}

static int dma_debug_device_change(struct notifier_block *nb, unsigned long action, void *data)
{
        struct device *dev = data;
        struct dma_debug_entry *uninitialized_var(entry);
        int count;

        if (dma_debug_disabled())
                return 0;

        switch (action) {
        case BUS_NOTIFY_UNBOUND_DRIVER:
                count = device_dma_allocations(dev, &entry);
                if (count == 0)
                        break;
                err_printk(dev, entry, "DMA-API: device driver has pending "
                                "DMA allocations while released from device "
                                "[count=%d]\n"
                                "One of leaked entries details: "
                                "[device address=0x%016llx] [size=%llu bytes] "
                                "[mapped with %s] [mapped as %s]\n",
                        count, entry->dev_addr, entry->size,
                        dir2name[entry->direction], type2name[entry->type]);
                break;
        default:
                break;
        }

        return 0;
}

void dma_debug_add_bus(struct bus_type *bus)
{
        struct notifier_block *nb;

        if (dma_debug_disabled())
                return;

        nb = kzalloc(sizeof(struct notifier_block), GFP_KERNEL);
        if (nb == NULL) {
                pr_err("dma_debug_add_bus: out of memory\n");
                return;
        }

        nb->notifier_call = dma_debug_device_change;

        bus_register_notifier(bus, nb);
}

/*
 * Let the architectures decide how many entries should be preallocated.
 */
void dma_debug_init(u32 num_entries)
{
        int i;

        /* Do not use dma_debug_initialized here, since we really want to be
         * called to set dma_debug_initialized
         */
        if (global_disable)
                return;

        for (i = 0; i < HASH_SIZE; ++i) {
                INIT_LIST_HEAD(&dma_entry_hash[i].list);
                spin_lock_init(&dma_entry_hash[i].lock);
        }

        if (dma_debug_fs_init() != 0) {
                pr_err("DMA-API: error creating debugfs entries - disabling\n");
                global_disable = true;

                return;
        }

        if (req_entries)
                num_entries = req_entries;

        if (prealloc_memory(num_entries) != 0) {
                pr_err("DMA-API: debugging out of memory error - disabled\n");
                global_disable = true;

                return;
        }

        nr_total_entries = num_free_entries;

        dma_debug_initialized = true;

        pr_info("DMA-API: debugging enabled by kernel config\n");
}

static __init int dma_debug_cmdline(char *str)
{
        if (!str)
                return -EINVAL;

        if (strncmp(str, "off", 3) == 0) {
                pr_info("DMA-API: debugging disabled on kernel command line\n");
                global_disable = true;
        }

        return 0;
}

static __init int dma_debug_entries_cmdline(char *str)
{
        int res;

        if (!str)
                return -EINVAL;

        res = get_option(&str, &req_entries);

        if (!res)
                req_entries = 0;

        return 0;
}

__setup("dma_debug=", dma_debug_cmdline);
__setup("dma_debug_entries=", dma_debug_entries_cmdline);

static void check_unmap(struct dma_debug_entry *ref)
{
        struct dma_debug_entry *entry;
        struct hash_bucket *bucket;
        unsigned long flags;

        bucket = get_hash_bucket(ref, &flags);
        entry = bucket_find_exact(bucket, ref);

        if (!entry) {
                /* must drop lock before calling dma_mapping_error */
                put_hash_bucket(bucket, &flags);

                if (dma_mapping_error(ref->dev, ref->dev_addr)) {
                        err_printk(ref->dev, NULL,
                                   "DMA-API: device driver tries to free an "
                                   "invalid DMA memory address\n");
                } else {
                        err_printk(ref->dev, NULL,
                                   "DMA-API: device driver tries to free DMA "
                                   "memory it has not allocated [device "
                                   "address=0x%016llx] [size=%llu bytes]\n",
                                   ref->dev_addr, ref->size);
                }
                return;
        }

        if (ref->size != entry->size) {
                err_printk(ref->dev, entry, "DMA-API: device driver frees "
                           "DMA memory with different size "
                           "[device address=0x%016llx] [map size=%llu bytes] "
                           "[unmap size=%llu bytes]\n",
                           ref->dev_addr, entry->size, ref->size);
        }

        if (ref->type != entry->type) {
                err_printk(ref->dev, entry, "DMA-API: device driver frees "
                           "DMA memory with wrong function "
                           "[device address=0x%016llx] [size=%llu bytes] "
                           "[mapped as %s] [unmapped as %s]\n",
                           ref->dev_addr, ref->size,
                           type2name[entry->type], type2name[ref->type]);
        } else if ((entry->type == dma_debug_coherent) &&
                   (phys_addr(ref) != phys_addr(entry))) {
                err_printk(ref->dev, entry, "DMA-API: device driver frees "
                           "DMA memory with different CPU address "
                           "[device address=0x%016llx] [size=%llu bytes] "
                           "[cpu alloc address=0x%016llx] "
                           "[cpu free address=0x%016llx]",
                           ref->dev_addr, ref->size,
                           phys_addr(entry),
                           phys_addr(ref));
        }

        if (ref->sg_call_ents && ref->type == dma_debug_sg &&
            ref->sg_call_ents != entry->sg_call_ents) {
                err_printk(ref->dev, entry, "DMA-API: device driver frees "
                           "DMA sg list with different entry count "
                           "[map count=%d] [unmap count=%d]\n",
                           entry->sg_call_ents, ref->sg_call_ents);
        }

        /*
         * This may be no bug in reality - but most implementations of the
         * DMA API don't handle this properly, so check for it here
         */
        if (ref->direction != entry->direction) {
                err_printk(ref->dev, entry, "DMA-API: device driver frees "
                           "DMA memory with different direction "
                           "[device address=0x%016llx] [size=%llu bytes] "
                           "[mapped with %s] [unmapped with %s]\n",
                           ref->dev_addr, ref->size,
                           dir2name[entry->direction],
                           dir2name[ref->direction]);
        }

        if (entry->map_err_type == MAP_ERR_NOT_CHECKED) {
                err_printk(ref->dev, entry,
                           "DMA-API: device driver failed to check map error"
                           "[device address=0x%016llx] [size=%llu bytes] "
                           "[mapped as %s]",
                           ref->dev_addr, ref->size,
                           type2name[entry->type]);
        }

        hash_bucket_del(entry);
        dma_entry_free(entry);

        put_hash_bucket(bucket, &flags);
}

static void check_for_stack(struct device *dev, void *addr)
{
        if (object_is_on_stack(addr))
                err_printk(dev, NULL, "DMA-API: device driver maps memory from "
                                "stack [addr=%p]\n", addr);
}

static inline bool overlap(void *addr, unsigned long len, void *start, void *end)
{
        unsigned long a1 = (unsigned long)addr;
        unsigned long b1 = a1 + len;
        unsigned long a2 = (unsigned long)start;
        unsigned long b2 = (unsigned long)end;

        return !(b1 <= a2 || a1 >= b2);
}

static void check_for_illegal_area(struct device *dev, void *addr, unsigned long len)
{
        if (overlap(addr, len, _text, _etext) ||
            overlap(addr, len, __start_rodata, __end_rodata))
                err_printk(dev, NULL, "DMA-API: device driver maps memory from kernel text or rodata [addr=%p] [len=%lu]\n", addr, len);
}

static void check_sync(struct device *dev,
                       struct dma_debug_entry *ref,
                       bool to_cpu)
{
        struct dma_debug_entry *entry;
        struct hash_bucket *bucket;
        unsigned long flags;

        bucket = get_hash_bucket(ref, &flags);

        entry = bucket_find_contain(&bucket, ref, &flags);

        if (!entry) {
                err_printk(dev, NULL, "DMA-API: device driver tries "
                                "to sync DMA memory it has not allocated "
                                "[device address=0x%016llx] [size=%llu bytes]\n",
                                (unsigned long long)ref->dev_addr, ref->size);
                goto out;
        }

        if (ref->size > entry->size) {
                err_printk(dev, entry, "DMA-API: device driver syncs"
                                " DMA memory outside allocated range "
                                "[device address=0x%016llx] "
                                "[allocation size=%llu bytes] "
                                "[sync offset+size=%llu]\n",
                                entry->dev_addr, entry->size,
                                ref->size);
        }

        if (entry->direction == DMA_BIDIRECTIONAL)
                goto out;

        if (ref->direction != entry->direction) {
                err_printk(dev, entry, "DMA-API: device driver syncs "
                                "DMA memory with different direction "
                                "[device address=0x%016llx] [size=%llu bytes] "
                                "[mapped with %s] [synced with %s]\n",
                                (unsigned long long)ref->dev_addr, entry->size,
                                dir2name[entry->direction],
                                dir2name[ref->direction]);
        }

        if (to_cpu && !(entry->direction == DMA_FROM_DEVICE) &&
                      !(ref->direction == DMA_TO_DEVICE))
                err_printk(dev, entry, "DMA-API: device driver syncs "
                                "device read-only DMA memory for cpu "
                                "[device address=0x%016llx] [size=%llu bytes] "
                                "[mapped with %s] [synced with %s]\n",
                                (unsigned long long)ref->dev_addr, entry->size,
                                dir2name[entry->direction],
                                dir2name[ref->direction]);

        if (!to_cpu && !(entry->direction == DMA_TO_DEVICE) &&
                       !(ref->direction == DMA_FROM_DEVICE))
                err_printk(dev, entry, "DMA-API: device driver syncs "
                                "device write-only DMA memory to device "
                                "[device address=0x%016llx] [size=%llu bytes] "
                                "[mapped with %s] [synced with %s]\n",
                                (unsigned long long)ref->dev_addr, entry->size,
                                dir2name[entry->direction],
                                dir2name[ref->direction]);

out:
        put_hash_bucket(bucket, &flags);
}

void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
                        size_t size, int direction, dma_addr_t dma_addr,
                        bool map_single)
{
        struct dma_debug_entry *entry;

        if (unlikely(dma_debug_disabled()))
                return;

        if (dma_mapping_error(dev, dma_addr))
                return;

        entry = dma_entry_alloc();
        if (!entry)
                return;

        entry->dev       = dev;
        entry->type      = dma_debug_page;
        entry->pfn       = page_to_pfn(page);
        entry->offset    = offset,
        entry->dev_addr  = dma_addr;
        entry->size      = size;
        entry->direction = direction;
        entry->map_err_type = MAP_ERR_NOT_CHECKED;

        if (map_single)
                entry->type = dma_debug_single;

        if (!PageHighMem(page)) {
                void *addr = page_address(page) + offset;

                check_for_stack(dev, addr);
                check_for_illegal_area(dev, addr, size);
        }

        add_dma_entry(entry);
}
EXPORT_SYMBOL(debug_dma_map_page);

void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
{
        struct dma_debug_entry ref;
        struct dma_debug_entry *entry;
        struct hash_bucket *bucket;
        unsigned long flags;

        if (unlikely(dma_debug_disabled()))
                return;

        ref.dev = dev;
        ref.dev_addr = dma_addr;
        bucket = get_hash_bucket(&ref, &flags);

        list_for_each_entry(entry, &bucket->list, list) {
                if (!exact_match(&ref, entry))
                        continue;

                /*
                 * The same physical address can be mapped multiple
                 * times. Without a hardware IOMMU this results in the
                 * same device addresses being put into the dma-debug
                 * hash multiple times too. This can result in false
                 * positives being reported. Therefore we implement a
                 * best-fit algorithm here which updates the first entry
                 * from the hash which fits the reference value and is
                 * not currently listed as being checked.
                 */
                if (entry->map_err_type == MAP_ERR_NOT_CHECKED) {
                        entry->map_err_type = MAP_ERR_CHECKED;
                        break;
                }
        }

        put_hash_bucket(bucket, &flags);
}
EXPORT_SYMBOL(debug_dma_mapping_error);

void debug_dma_unmap_page(struct device *dev, dma_addr_t addr,
                          size_t size, int direction, bool map_single)
{
        struct dma_debug_entry ref = {
                .type           = dma_debug_page,
                .dev            = dev,
                .dev_addr       = addr,
                .size           = size,
                .direction      = direction,
        };

        if (unlikely(dma_debug_disabled()))
                return;

        if (map_single)
                ref.type = dma_debug_single;

        check_unmap(&ref);
}
EXPORT_SYMBOL(debug_dma_unmap_page);

void debug_dma_map_sg(struct device *dev, struct scatterlist *sg,
                      int nents, int mapped_ents, int direction)
{
        struct dma_debug_entry *entry;
        struct scatterlist *s;
        int i;

        if (unlikely(dma_debug_disabled()))
                return;

        for_each_sg(sg, s, mapped_ents, i) {
                entry = dma_entry_alloc();
                if (!entry)
                        return;

                entry->type           = dma_debug_sg;
                entry->dev            = dev;
                entry->pfn            = page_to_pfn(sg_page(s));
                entry->offset         = s->offset,
                entry->size           = sg_dma_len(s);
                entry->dev_addr       = sg_dma_address(s);
                entry->direction      = direction;
                entry->sg_call_ents   = nents;
                entry->sg_mapped_ents = mapped_ents;

                if (!PageHighMem(sg_page(s))) {
                        check_for_stack(dev, sg_virt(s));
                        check_for_illegal_area(dev, sg_virt(s), sg_dma_len(s));
                }

                add_dma_entry(entry);
        }
}
EXPORT_SYMBOL(debug_dma_map_sg);

static int get_nr_mapped_entries(struct device *dev,
                                 struct dma_debug_entry *ref)
{
        struct dma_debug_entry *entry;
        struct hash_bucket *bucket;
        unsigned long flags;
        int mapped_ents;

        bucket       = get_hash_bucket(ref, &flags);
        entry        = bucket_find_exact(bucket, ref);
        mapped_ents  = 0;

        if (entry)
                mapped_ents = entry->sg_mapped_ents;
        put_hash_bucket(bucket, &flags);

        return mapped_ents;
}

void debug_dma_unmap_sg(struct device *dev, struct scatterlist *sglist,
                        int nelems, int dir)
{
        struct scatterlist *s;
        int mapped_ents = 0, i;

        if (unlikely(dma_debug_disabled()))
                return;

        for_each_sg(sglist, s, nelems, i) {

                struct dma_debug_entry ref = {
                        .type           = dma_debug_sg,
                        .dev            = dev,
                        .pfn            = page_to_pfn(sg_page(s)),
                        .offset         = s->offset,
                        .dev_addr       = sg_dma_address(s),
                        .size           = sg_dma_len(s),
                        .direction      = dir,
                        .sg_call_ents   = nelems,
                };

                if (mapped_ents && i >= mapped_ents)
                        break;

                if (!i)
                        mapped_ents = get_nr_mapped_entries(dev, &ref);

                check_unmap(&ref);
        }
}
EXPORT_SYMBOL(debug_dma_unmap_sg);

void debug_dma_alloc_coherent(struct device *dev, size_t size,
                              dma_addr_t dma_addr, void *virt)
{
        struct dma_debug_entry *entry;

        if (unlikely(dma_debug_disabled()))
                return;

        if (unlikely(virt == NULL))
                return;

        entry = dma_entry_alloc();
        if (!entry)
                return;

        entry->type      = dma_debug_coherent;
        entry->dev       = dev;
        entry->pfn       = page_to_pfn(virt_to_page(virt));
        entry->offset    = (size_t) virt & PAGE_MASK;
        entry->size      = size;
        entry->dev_addr  = dma_addr;
        entry->direction = DMA_BIDIRECTIONAL;

        add_dma_entry(entry);
}
EXPORT_SYMBOL(debug_dma_alloc_coherent);

void debug_dma_free_coherent(struct device *dev, size_t size,
                         void *virt, dma_addr_t addr)
{
        struct dma_debug_entry ref = {
                .type           = dma_debug_coherent,
                .dev            = dev,
                .pfn            = page_to_pfn(virt_to_page(virt)),
                .offset         = (size_t) virt & PAGE_MASK,
                .dev_addr       = addr,
                .size           = size,
                .direction      = DMA_BIDIRECTIONAL,
        };

        if (unlikely(dma_debug_disabled()))
                return;

        check_unmap(&ref);
}
EXPORT_SYMBOL(debug_dma_free_coherent);

void debug_dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle,
                                   size_t size, int direction)
{
        struct dma_debug_entry ref;

        if (unlikely(dma_debug_disabled()))
                return;

        ref.type         = dma_debug_single;
        ref.dev          = dev;
        ref.dev_addr     = dma_handle;
        ref.size         = size;
        ref.direction    = direction;
        ref.sg_call_ents = 0;

        check_sync(dev, &ref, true);
}
EXPORT_SYMBOL(debug_dma_sync_single_for_cpu);

void debug_dma_sync_single_for_device(struct device *dev,
                                      dma_addr_t dma_handle, size_t size,
                                      int direction)
{
        struct dma_debug_entry ref;

        if (unlikely(dma_debug_disabled()))
                return;

        ref.type         = dma_debug_single;
        ref.dev          = dev;
        ref.dev_addr     = dma_handle;
        ref.size         = size;
        ref.direction    = direction;
        ref.sg_call_ents = 0;

        check_sync(dev, &ref, false);
}
EXPORT_SYMBOL(debug_dma_sync_single_for_device);

void debug_dma_sync_single_range_for_cpu(struct device *dev,
                                         dma_addr_t dma_handle,
                                         unsigned long offset, size_t size,
                                         int direction)
{
        struct dma_debug_entry ref;

        if (unlikely(dma_debug_disabled()))
                return;

        ref.type         = dma_debug_single;
        ref.dev          = dev;
        ref.dev_addr     = dma_handle;
        ref.size         = offset + size;
        ref.direction    = direction;
        ref.sg_call_ents = 0;

        check_sync(dev, &ref, true);
}
EXPORT_SYMBOL(debug_dma_sync_single_range_for_cpu);

void debug_dma_sync_single_range_for_device(struct device *dev,
                                            dma_addr_t dma_handle,
                                            unsigned long offset,
                                            size_t size, int direction)
{
        struct dma_debug_entry ref;

        if (unlikely(dma_debug_disabled()))
                return;

        ref.type         = dma_debug_single;
        ref.dev          = dev;
        ref.dev_addr     = dma_handle;
        ref.size         = offset + size;
        ref.direction    = direction;
        ref.sg_call_ents = 0;

        check_sync(dev, &ref, false);
}
EXPORT_SYMBOL(debug_dma_sync_single_range_for_device);

void debug_dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
                               int nelems, int direction)
{
        struct scatterlist *s;
        int mapped_ents = 0, i;

        if (unlikely(dma_debug_disabled()))
                return;

        for_each_sg(sg, s, nelems, i) {

                struct dma_debug_entry ref = {
                        .type           = dma_debug_sg,
                        .dev            = dev,
                        .pfn            = page_to_pfn(sg_page(s)),
                        .offset         = s->offset,
                        .dev_addr       = sg_dma_address(s),
                        .size           = sg_dma_len(s),
                        .direction      = direction,
                        .sg_call_ents   = nelems,
                };

                if (!i)
                        mapped_ents = get_nr_mapped_entries(dev, &ref);

                if (i >= mapped_ents)
                        break;

                check_sync(dev, &ref, true);
        }
}
EXPORT_SYMBOL(debug_dma_sync_sg_for_cpu);

void debug_dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
                                  int nelems, int direction)
{
        struct scatterlist *s;
        int mapped_ents = 0, i;

        if (unlikely(dma_debug_disabled()))
                return;

        for_each_sg(sg, s, nelems, i) {

                struct dma_debug_entry ref = {
                        .type           = dma_debug_sg,
                        .dev            = dev,
                        .pfn            = page_to_pfn(sg_page(s)),
                        .offset         = s->offset,
                        .dev_addr       = sg_dma_address(s),
                        .size           = sg_dma_len(s),
                        .direction      = direction,
                        .sg_call_ents   = nelems,
                };
                if (!i)
                        mapped_ents = get_nr_mapped_entries(dev, &ref);

                if (i >= mapped_ents)
                        break;

                check_sync(dev, &ref, false);
        }
}
EXPORT_SYMBOL(debug_dma_sync_sg_for_device);

static int __init dma_debug_driver_setup(char *str)
{
        int i;

        for (i = 0; i < NAME_MAX_LEN - 1; ++i, ++str) {
                current_driver_name[i] = *str;
                if (*str == 0)
                        break;
        }

        if (current_driver_name[0])
                pr_info("DMA-API: enable driver filter for driver [%s]\n",
                        current_driver_name);


        return 1;
}
__setup("dma_debug_driver=", dma_debug_driver_setup);