xref: /linux/kernel/dma/debug.c (revision 0f3ad9c6105f32d1755c0bd54a7f98c892f3ceb7)

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2008 Advanced Micro Devices, Inc.
 *
 * Author: Joerg Roedel <joerg.roedel@amd.com>
 */

#define pr_fmt(fmt)	"DMA-API: " fmt

#include <linux/sched/task_stack.h>
#include <linux/scatterlist.h>
#include <linux/dma-map-ops.h>
#include <linux/sched/task.h>
#include <linux/stacktrace.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.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 <linux/swiotlb.h>
#include <asm/sections.h>
#include "debug.h"

#define HASH_SIZE       16384ULL
#define HASH_FN_SHIFT   13
#define HASH_FN_MASK    (HASH_SIZE - 1)

#define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)
/* If the pool runs out, add this many new entries at once */
#define DMA_DEBUG_DYNAMIC_ENTRIES (PAGE_SIZE / sizeof(struct dma_debug_entry))

enum {
	dma_debug_single,
	dma_debug_sg,
	dma_debug_coherent,
	dma_debug_noncoherent,
	dma_debug_phy,
};

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
 * @dev_addr: dma address
 * @size: length of the mapping
 * @type: single, page, sg, coherent
 * @direction: enum dma_data_direction
 * @sg_call_ents: 'nents' from dma_map_sg
 * @sg_mapped_ents: 'mapped_ents' from dma_map_sg
 * @paddr: physical start address of the mapping
 * @map_err_type: track whether dma_mapping_error() was checked
 * @stack_len: number of backtrace entries in @stack_entries
 * @stack_entries: stack of backtrace history
 */
struct dma_debug_entry {
	struct list_head list;
	struct device    *dev;
	u64              dev_addr;
	u64              size;
	int              type;
	int              direction;
	int		 sg_call_ents;
	int		 sg_mapped_ents;
	phys_addr_t	 paddr;
	enum map_err_types  map_err_type;
#ifdef CONFIG_STACKTRACE
	unsigned int	stack_len;
	unsigned long	stack_entries[DMA_DEBUG_STACKTRACE_ENTRIES];
#endif
} ____cacheline_aligned_in_smp;

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

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

/* 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 bool 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 nr_prealloc_entries = PREALLOC_DMA_DEBUG_ENTRIES;

/* 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[] = {
	[dma_debug_single] = "single",
	[dma_debug_sg] = "scatter-gather",
	[dma_debug_coherent] = "coherent",
	[dma_debug_noncoherent] = "noncoherent",
	[dma_debug_phy] = "phy",
};

static const char *dir2name[] = {
	[DMA_BIDIRECTIONAL]	= "DMA_BIDIRECTIONAL",
	[DMA_TO_DEVICE]		= "DMA_TO_DEVICE",
	[DMA_FROM_DEVICE]	= "DMA_FROM_DEVICE",
	[DMA_NONE]		= "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_warn("Mapped at:\n");
		stack_trace_print(entry->stack_entries, entry->stack_len, 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, pr_fmt("%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)
	__acquires(&dma_entry_hash[idx].lock)
{
	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)
	__releases(&bucket->lock)
{
	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)
{

	struct dma_debug_entry *entry, index = *ref;
	int limit = min(HASH_SIZE, (index.dev_addr >> HASH_FN_SHIFT) + 1);

	for (int i = 0; i < limit; i++) {
		entry = __hash_bucket_find(*bucket, ref, containing_match);

		if (entry)
			return entry;

		/*
		 * Nothing found, go back a hash bucket
		 */
		put_hash_bucket(*bucket, *flags);
		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);
}

/*
 * 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.
 *
 * Use __GFP_NOWARN because the printk from an OOM, to netconsole, could end
 * up right back in the DMA debugging code, leading to a deadlock.
 */
static RADIX_TREE(dma_active_cacheline, GFP_ATOMIC | __GFP_NOWARN);
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->paddr >> PAGE_SHIFT) << CACHELINE_PER_PAGE_SHIFT) +
		(offset_in_page(entry->paddr) >> 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.
	 */
	WARN_ONCE(overlap > ACTIVE_CACHELINE_MAX_OVERLAP,
		  pr_fmt("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);
}

/*
 * Dump mappings entries on kernel space for debugging purposes
 */
void debug_dma_dump_mappings(struct device *dev)
{
	int idx;
	phys_addr_t cln;

	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) {
				cln = to_cacheline_number(entry);
				dev_info(entry->dev,
					 "%s idx %d P=%pa D=%llx L=%llx cln=%pa %s %s\n",
					 type2name[entry->type], idx,
					 &entry->paddr, entry->dev_addr,
					 entry->size, &cln,
					 dir2name[entry->direction],
					 maperr2str[entry->map_err_type]);
			}
		}
		spin_unlock_irqrestore(&bucket->lock, flags);

		cond_resched();
	}
}

/*
 * Dump mappings entries on user space via debugfs
 */
static int dump_show(struct seq_file *seq, void *v)
{
	int idx;
	phys_addr_t cln;

	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) {
			cln = to_cacheline_number(entry);
			seq_printf(seq,
				   "%s %s %s idx %d P=%pa D=%llx L=%llx cln=%pa %s %s\n",
				   dev_driver_string(entry->dev),
				   dev_name(entry->dev),
				   type2name[entry->type], idx,
				   &entry->paddr, entry->dev_addr,
				   entry->size, &cln,
				   dir2name[entry->direction],
				   maperr2str[entry->map_err_type]);
		}
		spin_unlock_irqrestore(&bucket->lock, flags);
	}
	return 0;
}
DEFINE_SHOW_ATTRIBUTE(dump);

/*
 * 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, unsigned long attrs)
{
	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_once("cacheline tracking ENOMEM, dma-debug disabled\n");
		global_disable = true;
	} else if (rc == -EEXIST && !(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
		   !(IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) &&
		     is_swiotlb_active(entry->dev))) {
		err_printk(entry->dev, entry,
			"cacheline tracking EEXIST, overlapping mappings aren't supported\n");
	}
}

static int dma_debug_create_entries(gfp_t gfp)
{
	struct dma_debug_entry *entry;
	int i;

	entry = (void *)get_zeroed_page(gfp);
	if (!entry)
		return -ENOMEM;

	for (i = 0; i < DMA_DEBUG_DYNAMIC_ENTRIES; i++)
		list_add_tail(&entry[i].list, &free_entries);

	num_free_entries += DMA_DEBUG_DYNAMIC_ENTRIES;
	nr_total_entries += DMA_DEBUG_DYNAMIC_ENTRIES;

	return 0;
}

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;
}

/*
 * This should be called outside of free_entries_lock scope to avoid potential
 * deadlocks with serial consoles that use DMA.
 */
static void __dma_entry_alloc_check_leak(u32 nr_entries)
{
	u32 tmp = nr_entries % nr_prealloc_entries;

	/* Shout each time we tick over some multiple of the initial pool */
	if (tmp < DMA_DEBUG_DYNAMIC_ENTRIES) {
		pr_info("dma_debug_entry pool grown to %u (%u00%%)\n",
			nr_entries,
			(nr_entries / nr_prealloc_entries));
	}
}

/* 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)
{
	bool alloc_check_leak = false;
	struct dma_debug_entry *entry;
	unsigned long flags;
	u32 nr_entries;

	spin_lock_irqsave(&free_entries_lock, flags);
	if (num_free_entries == 0) {
		if (dma_debug_create_entries(GFP_ATOMIC)) {
			global_disable = true;
			spin_unlock_irqrestore(&free_entries_lock, flags);
			pr_err("debugging out of memory - disabling\n");
			return NULL;
		}
		alloc_check_leak = true;
		nr_entries = nr_total_entries;
	}

	entry = __dma_entry_alloc();

	spin_unlock_irqrestore(&free_entries_lock, flags);

	if (alloc_check_leak)
		__dma_entry_alloc_check_leak(nr_entries);

#ifdef CONFIG_STACKTRACE
	entry->stack_len = stack_trace_save(entry->stack_entries,
					    ARRAY_SIZE(entry->stack_entries),
					    1);
#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);
}

/*
 * 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 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("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("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 __init dma_debug_fs_init(void)
{
	struct dentry *dentry = debugfs_create_dir("dma-api", NULL);

	debugfs_create_bool("disabled", 0444, dentry, &global_disable);
	debugfs_create_u32("error_count", 0444, dentry, &error_count);
	debugfs_create_u32("all_errors", 0644, dentry, &show_all_errors);
	debugfs_create_u32("num_errors", 0644, dentry, &show_num_errors);
	debugfs_create_u32("num_free_entries", 0444, dentry, &num_free_entries);
	debugfs_create_u32("min_free_entries", 0444, dentry, &min_free_entries);
	debugfs_create_u32("nr_total_entries", 0444, dentry, &nr_total_entries);
	debugfs_create_file("driver_filter", 0644, dentry, NULL, &filter_fops);
	debugfs_create_file("dump", 0444, dentry, NULL, &dump_fops);

	return 0;
}
core_initcall_sync(dma_debug_fs_init);

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;

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

static int dma_debug_init(void)
{
	int i, nr_pages;

	/* Do not use dma_debug_initialized here, since we really want to be
	 * called to set dma_debug_initialized
	 */
	if (global_disable)
		return 0;

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

	nr_pages = DIV_ROUND_UP(nr_prealloc_entries, DMA_DEBUG_DYNAMIC_ENTRIES);
	for (i = 0; i < nr_pages; ++i)
		dma_debug_create_entries(GFP_KERNEL);
	if (num_free_entries >= nr_prealloc_entries) {
		pr_info("preallocated %d debug entries\n", nr_total_entries);
	} else if (num_free_entries > 0) {
		pr_warn("%d debug entries requested but only %d allocated\n",
			nr_prealloc_entries, nr_total_entries);
	} else {
		pr_err("debugging out of memory error - disabled\n");
		global_disable = true;

		return 0;
	}
	min_free_entries = num_free_entries;

	dma_debug_initialized = true;

	pr_info("debugging enabled by kernel config\n");
	return 0;
}
core_initcall(dma_debug_init);

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

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

	return 1;
}

static __init int dma_debug_entries_cmdline(char *str)
{
	if (!str)
		return -EINVAL;
	if (!get_option(&str, &nr_prealloc_entries))
		nr_prealloc_entries = PREALLOC_DMA_DEBUG_ENTRIES;
	return 1;
}

__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,
				   "device driver tries to free an "
				   "invalid DMA memory address\n");
		} else {
			err_printk(ref->dev, NULL,
				   "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, "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, "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 ||
		    entry->type == dma_debug_noncoherent) &&
		   ref->paddr != entry->paddr) {
		err_printk(ref->dev, entry, "device driver frees "
			   "DMA memory with different CPU address "
			   "[device address=0x%016llx] [size=%llu bytes] "
			   "[cpu alloc address=0x%pa] "
			   "[cpu free address=0x%pa]",
			   ref->dev_addr, ref->size,
			   &entry->paddr,
			   &ref->paddr);
	}

	if (ref->sg_call_ents && ref->type == dma_debug_sg &&
	    ref->sg_call_ents != entry->sg_call_ents) {
		err_printk(ref->dev, entry, "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, "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]);
	}

	/*
	 * Drivers should use dma_mapping_error() to check the returned
	 * addresses of dma_map_single() and dma_map_page().
	 * If not, print this warning message. See Documentation/core-api/dma-api.rst.
	 */
	if (entry->map_err_type == MAP_ERR_NOT_CHECKED) {
		err_printk(ref->dev, entry,
			   "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);
	put_hash_bucket(bucket, flags);

	/*
	 * Free the entry outside of bucket_lock to avoid ABBA deadlocks
	 * between that and radix_lock.
	 */
	dma_entry_free(entry);
}

static void check_for_stack(struct device *dev, phys_addr_t phys)
{
	void *addr;
	struct vm_struct *stack_vm_area = task_stack_vm_area(current);

	if (!stack_vm_area) {
		/* Stack is direct-mapped. */
		if (PhysHighMem(phys))
			return;
		addr = phys_to_virt(phys);
		if (object_is_on_stack(addr))
			err_printk(dev, NULL, "device driver maps memory from stack [addr=%p]\n", addr);
	} else {
		/* Stack is vmalloced. */
		int i;

		for (i = 0; i < stack_vm_area->nr_pages; i++) {
			if (__phys_to_pfn(phys) !=
			    page_to_pfn(stack_vm_area->pages[i]))
				continue;

			addr = (u8 *)current->stack + i * PAGE_SIZE +
			       (phys % PAGE_SIZE);
			err_printk(dev, NULL, "device driver maps memory from stack [probable addr=%p]\n", addr);
			break;
		}
	}
}

static void check_for_illegal_area(struct device *dev, void *addr, unsigned long len)
{
	if (memory_intersects(_stext, _etext, addr, len) ||
	    memory_intersects(__start_rodata, __end_rodata, addr, len))
		err_printk(dev, NULL, "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, "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, "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, "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, "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, "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]);

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

out:
	put_hash_bucket(bucket, flags);
}

static void check_sg_segment(struct device *dev, struct scatterlist *sg)
{
	unsigned int max_seg = dma_get_max_seg_size(dev);
	u64 start, end, boundary = dma_get_seg_boundary(dev);

	/*
	 * Either the driver forgot to set dma_parms appropriately, or
	 * whoever generated the list forgot to check them.
	 */
	if (sg->length > max_seg)
		err_printk(dev, NULL, "mapping sg segment longer than device claims to support [len=%u] [max=%u]\n",
			   sg->length, max_seg);
	/*
	 * In some cases this could potentially be the DMA API
	 * implementation's fault, but it would usually imply that
	 * the scatterlist was built inappropriately to begin with.
	 */
	start = sg_dma_address(sg);
	end = start + sg_dma_len(sg) - 1;
	if ((start ^ end) & ~boundary)
		err_printk(dev, NULL, "mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
			   start, end, boundary);
}

void debug_dma_map_single(struct device *dev, const void *addr,
			    unsigned long len)
{
	if (unlikely(dma_debug_disabled()))
		return;

	if (!virt_addr_valid(addr))
		err_printk(dev, NULL, "device driver maps memory from invalid area [addr=%p] [len=%lu]\n",
			   addr, len);

	if (is_vmalloc_addr(addr))
		err_printk(dev, NULL, "device driver maps memory from vmalloc area [addr=%p] [len=%lu]\n",
			   addr, len);
}
EXPORT_SYMBOL(debug_dma_map_single);

void debug_dma_map_phys(struct device *dev, phys_addr_t phys, size_t size,
		int direction, dma_addr_t dma_addr, unsigned long attrs)
{
	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_phy;
	entry->paddr	 = phys;
	entry->dev_addr  = dma_addr;
	entry->size      = size;
	entry->direction = direction;
	entry->map_err_type = MAP_ERR_NOT_CHECKED;

	if (!(attrs & DMA_ATTR_MMIO)) {
		check_for_stack(dev, phys);

		if (!PhysHighMem(phys))
			check_for_illegal_area(dev, phys_to_virt(phys), size);
	}

	add_dma_entry(entry, attrs);
}

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_phys(struct device *dev, dma_addr_t dma_addr,
			  size_t size, int direction)
{
	struct dma_debug_entry ref = {
		.type           = dma_debug_phy,
		.dev            = dev,
		.dev_addr       = dma_addr,
		.size           = size,
		.direction      = direction,
	};

	if (unlikely(dma_debug_disabled()))
		return;
	check_unmap(&ref);
}

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

	if (unlikely(dma_debug_disabled()))
		return;

	for_each_sg(sg, s, nents, i) {
		check_for_stack(dev, sg_phys(s));
		if (!PageHighMem(sg_page(s)))
			check_for_illegal_area(dev, sg_virt(s), s->length);
	}

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

		entry->type           = dma_debug_sg;
		entry->dev            = dev;
		entry->paddr	      = sg_phys(s);
		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;

		check_sg_segment(dev, s);

		add_dma_entry(entry, attrs);
	}
}

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,
			.paddr		= sg_phys(s),
			.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);
	}
}

static phys_addr_t virt_to_paddr(void *virt)
{
	struct page *page;

	if (is_vmalloc_addr(virt))
		page = vmalloc_to_page(virt);
	else
		page = virt_to_page(virt);

	return page_to_phys(page) + offset_in_page(virt);
}

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

	if (unlikely(dma_debug_disabled()))
		return;

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

	/* handle vmalloc and linear addresses */
	if (!is_vmalloc_addr(virt) && !virt_addr_valid(virt))
		return;

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

	entry->type      = dma_debug_coherent;
	entry->dev       = dev;
	entry->paddr	 = virt_to_paddr(virt);
	entry->size      = size;
	entry->dev_addr  = dma_addr;
	entry->direction = DMA_BIDIRECTIONAL;

	add_dma_entry(entry, attrs);
}

void debug_dma_free_coherent(struct device *dev, size_t size,
			 void *virt, dma_addr_t dma_addr)
{
	struct dma_debug_entry ref = {
		.type           = dma_debug_coherent,
		.dev            = dev,
		.dev_addr       = dma_addr,
		.size           = size,
		.direction      = DMA_BIDIRECTIONAL,
	};

	/* handle vmalloc and linear addresses */
	if (!is_vmalloc_addr(virt) && !virt_addr_valid(virt))
		return;

	ref.paddr = virt_to_paddr(virt);

	if (unlikely(dma_debug_disabled()))
		return;

	check_unmap(&ref);
}

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);
}

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);
}

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,
			.paddr		= sg_phys(s),
			.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);
	}
}

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,
			.paddr		= sg_phys(sg),
			.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);
	}
}

void debug_dma_alloc_pages(struct device *dev, struct page *page,
			   size_t size, int direction,
			   dma_addr_t dma_addr,
			   unsigned long attrs)
{
	struct dma_debug_entry *entry;

	if (unlikely(dma_debug_disabled()))
		return;

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

	entry->type      = dma_debug_noncoherent;
	entry->dev       = dev;
	entry->paddr	 = page_to_phys(page);
	entry->size      = size;
	entry->dev_addr  = dma_addr;
	entry->direction = direction;

	add_dma_entry(entry, attrs);
}

void debug_dma_free_pages(struct device *dev, struct page *page,
			  size_t size, int direction,
			  dma_addr_t dma_addr)
{
	struct dma_debug_entry ref = {
		.type           = dma_debug_noncoherent,
		.dev            = dev,
		.paddr		= page_to_phys(page),
		.dev_addr       = dma_addr,
		.size           = size,
		.direction      = direction,
	};

	if (unlikely(dma_debug_disabled()))
		return;

	check_unmap(&ref);
}

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("enable driver filter for driver [%s]\n",
			current_driver_name);


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