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/device.h>
#include <linux/types.h>
#include <linux/sched.h>
#include <linux/list.h>
#include <linux/slab.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,
};

#define DMA_DEBUG_STACKTRACE_ENTRIES 5

struct dma_debug_entry {
	struct list_head list;
	struct device    *dev;
	int              type;
	phys_addr_t      paddr;
	u64              dev_addr;
	u64              size;
	int              direction;
	int		 sg_call_ents;
	int		 sg_mapped_ents;
#ifdef CONFIG_STACKTRACE
	struct		 stack_trace stacktrace;
	unsigned long	 st_entries[DMA_DEBUG_STACKTRACE_ENTRIES];
#endif
};

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 bool global_disable __read_mostly;

/* 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;

/* 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 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) {
		printk(KERN_WARNING "Mapped at:\n");
		print_stack_trace(&entry->stacktrace, 0);
	}
#endif
}

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

/*
 * 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)
{
	struct dma_debug_entry *entry;

	list_for_each_entry(entry, &bucket->list, list) {
		if ((entry->dev_addr == ref->dev_addr) &&
		    (entry->dev == ref->dev))
			return entry;
	}

	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);
}

/*
 * 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 D=%Lx L=%Lx %s\n",
					 type2name[entry->type], idx,
					 (unsigned long long)entry->paddr,
					 entry->dev_addr, entry->size,
					 dir2name[entry->direction]);
			}
		}

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

/*
 * 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;

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

/* 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 = NULL;
	unsigned long flags;

	spin_lock_irqsave(&free_entries_lock, flags);

	if (list_empty(&free_entries)) {
		printk(KERN_ERR "DMA-API: debugging out of memory "
				"- disabling\n");
		global_disable = true;
		goto out;
	}

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

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

out:
	spin_unlock_irqrestore(&free_entries_lock, flags);

	return entry;
}

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

	/*
	 * 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 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;

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

	global_disable_dent = debugfs_create_bool("disabled", 0444,
			dma_debug_dent,
			(u32 *)&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;

	return 0;

out_err:
	debugfs_remove_recursive(dma_debug_dent);

	return -ENOMEM;
}


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

	if (global_disable)
		return;

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

	if (dma_debug_fs_init() != 0) {
		printk(KERN_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) {
		printk(KERN_ERR "DMA-API: debugging out of memory error "
				"- disabled\n");
		global_disable = true;

		return;
	}

	printk(KERN_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) {
		printk(KERN_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;

	if (dma_mapping_error(ref->dev, ref->dev_addr))
		return;

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

	if (!entry) {
		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);
		goto out;
	}

	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) &&
		   (ref->paddr != entry->paddr)) {
		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=%p] [cpu free address=%p]",
			   ref->dev_addr, ref->size,
			   (void *)entry->paddr, (void *)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, "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]);
	}

	hash_bucket_del(entry);
	dma_entry_free(entry);

out:
	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 void check_sync(struct device *dev, dma_addr_t addr,
		       u64 size, u64 offset, int direction, bool to_cpu)
{
	struct dma_debug_entry ref = {
		.dev            = dev,
		.dev_addr       = addr,
		.size           = size,
		.direction      = direction,
	};
	struct dma_debug_entry *entry;
	struct hash_bucket *bucket;
	unsigned long flags;

	bucket = get_hash_bucket(&ref, &flags);

	entry = hash_bucket_find(bucket, &ref);

	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",
				addr, size);
		goto out;
	}

	if ((offset + 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=%llu] "
				"[sync size=%llu]\n", entry->dev_addr, entry->size,
				offset, size);
	}

	if (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",
				addr, entry->size,
				dir2name[entry->direction],
				dir2name[direction]);
	}

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

	if (to_cpu && !(entry->direction == DMA_FROM_DEVICE) &&
		      !(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",
				addr, entry->size,
				dir2name[entry->direction],
				dir2name[direction]);

	if (!to_cpu && !(entry->direction == DMA_TO_DEVICE) &&
		       !(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",
				addr, entry->size,
				dir2name[entry->direction],
				dir2name[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(global_disable))
		return;

	if (unlikely(dma_mapping_error(dev, dma_addr)))
		return;

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

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

	if (map_single) {
		entry->type = dma_debug_single;
		check_for_stack(dev, page_address(page) + offset);
	}

	add_dma_entry(entry);
}
EXPORT_SYMBOL(debug_dma_map_page);

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(global_disable))
		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(global_disable))
		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->paddr          = sg_phys(s);
		entry->size           = s->length;
		entry->dev_addr       = s->dma_address;
		entry->direction      = direction;
		entry->sg_call_ents   = nents;
		entry->sg_mapped_ents = mapped_ents;

		check_for_stack(dev, sg_virt(s));

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

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

	if (unlikely(global_disable))
		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       = s->dma_address,
			.size           = s->length,
			.direction      = dir,
			.sg_call_ents   = 0,
		};

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

		if (mapped_ents == 0) {
			struct hash_bucket *bucket;
			ref.sg_call_ents = nelems;
			bucket = get_hash_bucket(&ref, &flags);
			entry = hash_bucket_find(bucket, &ref);
			if (entry)
				mapped_ents = entry->sg_mapped_ents;
			put_hash_bucket(bucket, &flags);
		}

		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(global_disable))
		return;

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

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

	entry->type      = dma_debug_coherent;
	entry->dev       = dev;
	entry->paddr     = virt_to_phys(virt);
	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,
		.paddr          = virt_to_phys(virt),
		.dev_addr       = addr,
		.size           = size,
		.direction      = DMA_BIDIRECTIONAL,
	};

	if (unlikely(global_disable))
		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)
{
	if (unlikely(global_disable))
		return;

	check_sync(dev, dma_handle, size, 0, direction, 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)
{
	if (unlikely(global_disable))
		return;

	check_sync(dev, dma_handle, size, 0, direction, 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)
{
	if (unlikely(global_disable))
		return;

	check_sync(dev, dma_handle, size, offset, direction, 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)
{
	if (unlikely(global_disable))
		return;

	check_sync(dev, dma_handle, size, offset, direction, 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 i;

	if (unlikely(global_disable))
		return;

	for_each_sg(sg, s, nelems, i) {
		check_sync(dev, s->dma_address, s->dma_length, 0,
				direction, 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 i;

	if (unlikely(global_disable))
		return;

	for_each_sg(sg, s, nelems, i) {
		check_sync(dev, s->dma_address, s->dma_length, 0,
				direction, false);
	}
}
EXPORT_SYMBOL(debug_dma_sync_sg_for_device);