Merge tag 'drm/tegra/for-5.7-fixes' of git://anongit.freedesktop.org/tegra/linux...

[thirdparty/linux.git] / drivers / dma / dmaengine.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright(c) 2004 - 2006 Intel Corporation. All rights reserved.
 */

/*
 * This code implements the DMA subsystem. It provides a HW-neutral interface
 * for other kernel code to use asynchronous memory copy capabilities,
 * if present, and allows different HW DMA drivers to register as providing
 * this capability.
 *
 * Due to the fact we are accelerating what is already a relatively fast
 * operation, the code goes to great lengths to avoid additional overhead,
 * such as locking.
 *
 * LOCKING:
 *
 * The subsystem keeps a global list of dma_device structs it is protected by a
 * mutex, dma_list_mutex.
 *
 * A subsystem can get access to a channel by calling dmaengine_get() followed
 * by dma_find_channel(), or if it has need for an exclusive channel it can call
 * dma_request_channel().  Once a channel is allocated a reference is taken
 * against its corresponding driver to disable removal.
 *
 * Each device has a channels list, which runs unlocked but is never modified
 * once the device is registered, it's just setup by the driver.
 *
 * See Documentation/driver-api/dmaengine for more details
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/platform_device.h>
#include <linux/dma-mapping.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/device.h>
#include <linux/dmaengine.h>
#include <linux/hardirq.h>
#include <linux/spinlock.h>
#include <linux/percpu.h>
#include <linux/rcupdate.h>
#include <linux/mutex.h>
#include <linux/jiffies.h>
#include <linux/rculist.h>
#include <linux/idr.h>
#include <linux/slab.h>
#include <linux/acpi.h>
#include <linux/acpi_dma.h>
#include <linux/of_dma.h>
#include <linux/mempool.h>
#include <linux/numa.h>

static DEFINE_MUTEX(dma_list_mutex);
static DEFINE_IDA(dma_ida);
static LIST_HEAD(dma_device_list);
static long dmaengine_ref_count;

/* --- debugfs implementation --- */
#ifdef CONFIG_DEBUG_FS
#include <linux/debugfs.h>

static struct dentry *rootdir;

static void dmaengine_debug_register(struct dma_device *dma_dev)
{
        dma_dev->dbg_dev_root = debugfs_create_dir(dev_name(dma_dev->dev),
                                                   rootdir);
        if (IS_ERR(dma_dev->dbg_dev_root))
                dma_dev->dbg_dev_root = NULL;
}

static void dmaengine_debug_unregister(struct dma_device *dma_dev)
{
        debugfs_remove_recursive(dma_dev->dbg_dev_root);
        dma_dev->dbg_dev_root = NULL;
}

static void dmaengine_dbg_summary_show(struct seq_file *s,
                                       struct dma_device *dma_dev)
{
        struct dma_chan *chan;

        list_for_each_entry(chan, &dma_dev->channels, device_node) {
                if (chan->client_count) {
                        seq_printf(s, " %-13s| %s", dma_chan_name(chan),
                                   chan->dbg_client_name ?: "in-use");

                        if (chan->router)
                                seq_printf(s, " (via router: %s)\n",
                                        dev_name(chan->router->dev));
                        else
                                seq_puts(s, "\n");
                }
        }
}

static int dmaengine_summary_show(struct seq_file *s, void *data)
{
        struct dma_device *dma_dev = NULL;

        mutex_lock(&dma_list_mutex);
        list_for_each_entry(dma_dev, &dma_device_list, global_node) {
                seq_printf(s, "dma%d (%s): number of channels: %u\n",
                           dma_dev->dev_id, dev_name(dma_dev->dev),
                           dma_dev->chancnt);

                if (dma_dev->dbg_summary_show)
                        dma_dev->dbg_summary_show(s, dma_dev);
                else
                        dmaengine_dbg_summary_show(s, dma_dev);

                if (!list_is_last(&dma_dev->global_node, &dma_device_list))
                        seq_puts(s, "\n");
        }
        mutex_unlock(&dma_list_mutex);

        return 0;
}
DEFINE_SHOW_ATTRIBUTE(dmaengine_summary);

static void __init dmaengine_debugfs_init(void)
{
        rootdir = debugfs_create_dir("dmaengine", NULL);

        /* /sys/kernel/debug/dmaengine/summary */
        debugfs_create_file("summary", 0444, rootdir, NULL,
                            &dmaengine_summary_fops);
}
#else
static inline void dmaengine_debugfs_init(void) { }
static inline int dmaengine_debug_register(struct dma_device *dma_dev)
{
        return 0;
}

static inline void dmaengine_debug_unregister(struct dma_device *dma_dev) { }
#endif  /* DEBUG_FS */

/* --- sysfs implementation --- */

#define DMA_SLAVE_NAME  "slave"

/**
 * dev_to_dma_chan - convert a device pointer to its sysfs container object
 * @dev - device node
 *
 * Must be called under dma_list_mutex
 */
static struct dma_chan *dev_to_dma_chan(struct device *dev)
{
        struct dma_chan_dev *chan_dev;

        chan_dev = container_of(dev, typeof(*chan_dev), device);
        return chan_dev->chan;
}

static ssize_t memcpy_count_show(struct device *dev,
                                 struct device_attribute *attr, char *buf)
{
        struct dma_chan *chan;
        unsigned long count = 0;
        int i;
        int err;

        mutex_lock(&dma_list_mutex);
        chan = dev_to_dma_chan(dev);
        if (chan) {
                for_each_possible_cpu(i)
                        count += per_cpu_ptr(chan->local, i)->memcpy_count;
                err = sprintf(buf, "%lu\n", count);
        } else
                err = -ENODEV;
        mutex_unlock(&dma_list_mutex);

        return err;
}
static DEVICE_ATTR_RO(memcpy_count);

static ssize_t bytes_transferred_show(struct device *dev,
                                      struct device_attribute *attr, char *buf)
{
        struct dma_chan *chan;
        unsigned long count = 0;
        int i;
        int err;

        mutex_lock(&dma_list_mutex);
        chan = dev_to_dma_chan(dev);
        if (chan) {
                for_each_possible_cpu(i)
                        count += per_cpu_ptr(chan->local, i)->bytes_transferred;
                err = sprintf(buf, "%lu\n", count);
        } else
                err = -ENODEV;
        mutex_unlock(&dma_list_mutex);

        return err;
}
static DEVICE_ATTR_RO(bytes_transferred);

static ssize_t in_use_show(struct device *dev, struct device_attribute *attr,
                           char *buf)
{
        struct dma_chan *chan;
        int err;

        mutex_lock(&dma_list_mutex);
        chan = dev_to_dma_chan(dev);
        if (chan)
                err = sprintf(buf, "%d\n", chan->client_count);
        else
                err = -ENODEV;
        mutex_unlock(&dma_list_mutex);

        return err;
}
static DEVICE_ATTR_RO(in_use);

static struct attribute *dma_dev_attrs[] = {
        &dev_attr_memcpy_count.attr,
        &dev_attr_bytes_transferred.attr,
        &dev_attr_in_use.attr,
        NULL,
};
ATTRIBUTE_GROUPS(dma_dev);

static void chan_dev_release(struct device *dev)
{
        struct dma_chan_dev *chan_dev;

        chan_dev = container_of(dev, typeof(*chan_dev), device);
        kfree(chan_dev);
}

static struct class dma_devclass = {
        .name           = "dma",
        .dev_groups     = dma_dev_groups,
        .dev_release    = chan_dev_release,
};

/* --- client and device registration --- */

/**
 * dma_cap_mask_all - enable iteration over all operation types
 */
static dma_cap_mask_t dma_cap_mask_all;

/**
 * dma_chan_tbl_ent - tracks channel allocations per core/operation
 * @chan - associated channel for this entry
 */
struct dma_chan_tbl_ent {
        struct dma_chan *chan;
};

/**
 * channel_table - percpu lookup table for memory-to-memory offload providers
 */
static struct dma_chan_tbl_ent __percpu *channel_table[DMA_TX_TYPE_END];

static int __init dma_channel_table_init(void)
{
        enum dma_transaction_type cap;
        int err = 0;

        bitmap_fill(dma_cap_mask_all.bits, DMA_TX_TYPE_END);

        /* 'interrupt', 'private', and 'slave' are channel capabilities,
         * but are not associated with an operation so they do not need
         * an entry in the channel_table
         */
        clear_bit(DMA_INTERRUPT, dma_cap_mask_all.bits);
        clear_bit(DMA_PRIVATE, dma_cap_mask_all.bits);
        clear_bit(DMA_SLAVE, dma_cap_mask_all.bits);

        for_each_dma_cap_mask(cap, dma_cap_mask_all) {
                channel_table[cap] = alloc_percpu(struct dma_chan_tbl_ent);
                if (!channel_table[cap]) {
                        err = -ENOMEM;
                        break;
                }
        }

        if (err) {
                pr_err("dmaengine dma_channel_table_init failure: %d\n", err);
                for_each_dma_cap_mask(cap, dma_cap_mask_all)
                        free_percpu(channel_table[cap]);
        }

        return err;
}
arch_initcall(dma_channel_table_init);

/**
 * dma_chan_is_local - returns true if the channel is in the same numa-node as
 *      the cpu
 */
static bool dma_chan_is_local(struct dma_chan *chan, int cpu)
{
        int node = dev_to_node(chan->device->dev);
        return node == NUMA_NO_NODE ||
                cpumask_test_cpu(cpu, cpumask_of_node(node));
}

/**
 * min_chan - returns the channel with min count and in the same numa-node as
 *      the cpu
 * @cap: capability to match
 * @cpu: cpu index which the channel should be close to
 *
 * If some channels are close to the given cpu, the one with the lowest
 * reference count is returned. Otherwise, cpu is ignored and only the
 * reference count is taken into account.
 * Must be called under dma_list_mutex.
 */
static struct dma_chan *min_chan(enum dma_transaction_type cap, int cpu)
{
        struct dma_device *device;
        struct dma_chan *chan;
        struct dma_chan *min = NULL;
        struct dma_chan *localmin = NULL;

        list_for_each_entry(device, &dma_device_list, global_node) {
                if (!dma_has_cap(cap, device->cap_mask) ||
                    dma_has_cap(DMA_PRIVATE, device->cap_mask))
                        continue;
                list_for_each_entry(chan, &device->channels, device_node) {
                        if (!chan->client_count)
                                continue;
                        if (!min || chan->table_count < min->table_count)
                                min = chan;

                        if (dma_chan_is_local(chan, cpu))
                                if (!localmin ||
                                    chan->table_count < localmin->table_count)
                                        localmin = chan;
                }
        }

        chan = localmin ? localmin : min;

        if (chan)
                chan->table_count++;

        return chan;
}

/**
 * dma_channel_rebalance - redistribute the available channels
 *
 * Optimize for cpu isolation (each cpu gets a dedicated channel for an
 * operation type) in the SMP case,  and operation isolation (avoid
 * multi-tasking channels) in the non-SMP case.  Must be called under
 * dma_list_mutex.
 */
static void dma_channel_rebalance(void)
{
        struct dma_chan *chan;
        struct dma_device *device;
        int cpu;
        int cap;

        /* undo the last distribution */
        for_each_dma_cap_mask(cap, dma_cap_mask_all)
                for_each_possible_cpu(cpu)
                        per_cpu_ptr(channel_table[cap], cpu)->chan = NULL;

        list_for_each_entry(device, &dma_device_list, global_node) {
                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
                        continue;
                list_for_each_entry(chan, &device->channels, device_node)
                        chan->table_count = 0;
        }

        /* don't populate the channel_table if no clients are available */
        if (!dmaengine_ref_count)
                return;

        /* redistribute available channels */
        for_each_dma_cap_mask(cap, dma_cap_mask_all)
                for_each_online_cpu(cpu) {
                        chan = min_chan(cap, cpu);
                        per_cpu_ptr(channel_table[cap], cpu)->chan = chan;
                }
}

static int dma_device_satisfies_mask(struct dma_device *device,
                                     const dma_cap_mask_t *want)
{
        dma_cap_mask_t has;

        bitmap_and(has.bits, want->bits, device->cap_mask.bits,
                DMA_TX_TYPE_END);
        return bitmap_equal(want->bits, has.bits, DMA_TX_TYPE_END);
}

static struct module *dma_chan_to_owner(struct dma_chan *chan)
{
        return chan->device->owner;
}

/**
 * balance_ref_count - catch up the channel reference count
 * @chan - channel to balance ->client_count versus dmaengine_ref_count
 *
 * balance_ref_count must be called under dma_list_mutex
 */
static void balance_ref_count(struct dma_chan *chan)
{
        struct module *owner = dma_chan_to_owner(chan);

        while (chan->client_count < dmaengine_ref_count) {
                __module_get(owner);
                chan->client_count++;
        }
}

static void dma_device_release(struct kref *ref)
{
        struct dma_device *device = container_of(ref, struct dma_device, ref);

        list_del_rcu(&device->global_node);
        dma_channel_rebalance();

        if (device->device_release)
                device->device_release(device);
}

static void dma_device_put(struct dma_device *device)
{
        lockdep_assert_held(&dma_list_mutex);
        kref_put(&device->ref, dma_device_release);
}

/**
 * dma_chan_get - try to grab a dma channel's parent driver module
 * @chan - channel to grab
 *
 * Must be called under dma_list_mutex
 */
static int dma_chan_get(struct dma_chan *chan)
{
        struct module *owner = dma_chan_to_owner(chan);
        int ret;

        /* The channel is already in use, update client count */
        if (chan->client_count) {
                __module_get(owner);
                goto out;
        }

        if (!try_module_get(owner))
                return -ENODEV;

        ret = kref_get_unless_zero(&chan->device->ref);
        if (!ret) {
                ret = -ENODEV;
                goto module_put_out;
        }

        /* allocate upon first client reference */
        if (chan->device->device_alloc_chan_resources) {
                ret = chan->device->device_alloc_chan_resources(chan);
                if (ret < 0)
                        goto err_out;
        }

        if (!dma_has_cap(DMA_PRIVATE, chan->device->cap_mask))
                balance_ref_count(chan);

out:
        chan->client_count++;
        return 0;

err_out:
        dma_device_put(chan->device);
module_put_out:
        module_put(owner);
        return ret;
}

/**
 * dma_chan_put - drop a reference to a dma channel's parent driver module
 * @chan - channel to release
 *
 * Must be called under dma_list_mutex
 */
static void dma_chan_put(struct dma_chan *chan)
{
        /* This channel is not in use, bail out */
        if (!chan->client_count)
                return;

        chan->client_count--;

        /* This channel is not in use anymore, free it */
        if (!chan->client_count && chan->device->device_free_chan_resources) {
                /* Make sure all operations have completed */
                dmaengine_synchronize(chan);
                chan->device->device_free_chan_resources(chan);
        }

        /* If the channel is used via a DMA request router, free the mapping */
        if (chan->router && chan->router->route_free) {
                chan->router->route_free(chan->router->dev, chan->route_data);
                chan->router = NULL;
                chan->route_data = NULL;
        }

        dma_device_put(chan->device);
        module_put(dma_chan_to_owner(chan));
}

enum dma_status dma_sync_wait(struct dma_chan *chan, dma_cookie_t cookie)
{
        enum dma_status status;
        unsigned long dma_sync_wait_timeout = jiffies + msecs_to_jiffies(5000);

        dma_async_issue_pending(chan);
        do {
                status = dma_async_is_tx_complete(chan, cookie, NULL, NULL);
                if (time_after_eq(jiffies, dma_sync_wait_timeout)) {
                        dev_err(chan->device->dev, "%s: timeout!\n", __func__);
                        return DMA_ERROR;
                }
                if (status != DMA_IN_PROGRESS)
                        break;
                cpu_relax();
        } while (1);

        return status;
}
EXPORT_SYMBOL(dma_sync_wait);

/**
 * dma_find_channel - find a channel to carry out the operation
 * @tx_type: transaction type
 */
struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type)
{
        return this_cpu_read(channel_table[tx_type]->chan);
}
EXPORT_SYMBOL(dma_find_channel);

/**
 * dma_issue_pending_all - flush all pending operations across all channels
 */
void dma_issue_pending_all(void)
{
        struct dma_device *device;
        struct dma_chan *chan;

        rcu_read_lock();
        list_for_each_entry_rcu(device, &dma_device_list, global_node) {
                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
                        continue;
                list_for_each_entry(chan, &device->channels, device_node)
                        if (chan->client_count)
                                device->device_issue_pending(chan);
        }
        rcu_read_unlock();
}
EXPORT_SYMBOL(dma_issue_pending_all);

int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
{
        struct dma_device *device;

        if (!chan || !caps)
                return -EINVAL;

        device = chan->device;

        /* check if the channel supports slave transactions */
        if (!(test_bit(DMA_SLAVE, device->cap_mask.bits) ||
              test_bit(DMA_CYCLIC, device->cap_mask.bits)))
                return -ENXIO;

        /*
         * Check whether it reports it uses the generic slave
         * capabilities, if not, that means it doesn't support any
         * kind of slave capabilities reporting.
         */
        if (!device->directions)
                return -ENXIO;

        caps->src_addr_widths = device->src_addr_widths;
        caps->dst_addr_widths = device->dst_addr_widths;
        caps->directions = device->directions;
        caps->max_burst = device->max_burst;
        caps->residue_granularity = device->residue_granularity;
        caps->descriptor_reuse = device->descriptor_reuse;
        caps->cmd_pause = !!device->device_pause;
        caps->cmd_resume = !!device->device_resume;
        caps->cmd_terminate = !!device->device_terminate_all;

        return 0;
}
EXPORT_SYMBOL_GPL(dma_get_slave_caps);

static struct dma_chan *private_candidate(const dma_cap_mask_t *mask,
                                          struct dma_device *dev,
                                          dma_filter_fn fn, void *fn_param)
{
        struct dma_chan *chan;

        if (mask && !dma_device_satisfies_mask(dev, mask)) {
                dev_dbg(dev->dev, "%s: wrong capabilities\n", __func__);
                return NULL;
        }
        /* devices with multiple channels need special handling as we need to
         * ensure that all channels are either private or public.
         */
        if (dev->chancnt > 1 && !dma_has_cap(DMA_PRIVATE, dev->cap_mask))
                list_for_each_entry(chan, &dev->channels, device_node) {
                        /* some channels are already publicly allocated */
                        if (chan->client_count)
                                return NULL;
                }

        list_for_each_entry(chan, &dev->channels, device_node) {
                if (chan->client_count) {
                        dev_dbg(dev->dev, "%s: %s busy\n",
                                 __func__, dma_chan_name(chan));
                        continue;
                }
                if (fn && !fn(chan, fn_param)) {
                        dev_dbg(dev->dev, "%s: %s filter said false\n",
                                 __func__, dma_chan_name(chan));
                        continue;
                }
                return chan;
        }

        return NULL;
}

static struct dma_chan *find_candidate(struct dma_device *device,
                                       const dma_cap_mask_t *mask,
                                       dma_filter_fn fn, void *fn_param)
{
        struct dma_chan *chan = private_candidate(mask, device, fn, fn_param);
        int err;

        if (chan) {
                /* Found a suitable channel, try to grab, prep, and return it.
                 * We first set DMA_PRIVATE to disable balance_ref_count as this
                 * channel will not be published in the general-purpose
                 * allocator
                 */
                dma_cap_set(DMA_PRIVATE, device->cap_mask);
                device->privatecnt++;
                err = dma_chan_get(chan);

                if (err) {
                        if (err == -ENODEV) {
                                dev_dbg(device->dev, "%s: %s module removed\n",
                                        __func__, dma_chan_name(chan));
                                list_del_rcu(&device->global_node);
                        } else
                                dev_dbg(device->dev,
                                        "%s: failed to get %s: (%d)\n",
                                         __func__, dma_chan_name(chan), err);

                        if (--device->privatecnt == 0)
                                dma_cap_clear(DMA_PRIVATE, device->cap_mask);

                        chan = ERR_PTR(err);
                }
        }

        return chan ? chan : ERR_PTR(-EPROBE_DEFER);
}

/**
 * dma_get_slave_channel - try to get specific channel exclusively
 * @chan: target channel
 */
struct dma_chan *dma_get_slave_channel(struct dma_chan *chan)
{
        int err = -EBUSY;

        /* lock against __dma_request_channel */
        mutex_lock(&dma_list_mutex);

        if (chan->client_count == 0) {
                struct dma_device *device = chan->device;

                dma_cap_set(DMA_PRIVATE, device->cap_mask);
                device->privatecnt++;
                err = dma_chan_get(chan);
                if (err) {
                        dev_dbg(chan->device->dev,
                                "%s: failed to get %s: (%d)\n",
                                __func__, dma_chan_name(chan), err);
                        chan = NULL;
                        if (--device->privatecnt == 0)
                                dma_cap_clear(DMA_PRIVATE, device->cap_mask);
                }
        } else
                chan = NULL;

        mutex_unlock(&dma_list_mutex);


        return chan;
}
EXPORT_SYMBOL_GPL(dma_get_slave_channel);

struct dma_chan *dma_get_any_slave_channel(struct dma_device *device)
{
        dma_cap_mask_t mask;
        struct dma_chan *chan;

        dma_cap_zero(mask);
        dma_cap_set(DMA_SLAVE, mask);

        /* lock against __dma_request_channel */
        mutex_lock(&dma_list_mutex);

        chan = find_candidate(device, &mask, NULL, NULL);

        mutex_unlock(&dma_list_mutex);

        return IS_ERR(chan) ? NULL : chan;
}
EXPORT_SYMBOL_GPL(dma_get_any_slave_channel);

/**
 * __dma_request_channel - try to allocate an exclusive channel
 * @mask: capabilities that the channel must satisfy
 * @fn: optional callback to disposition available channels
 * @fn_param: opaque parameter to pass to dma_filter_fn
 * @np: device node to look for DMA channels
 *
 * Returns pointer to appropriate DMA channel on success or NULL.
 */
struct dma_chan *__dma_request_channel(const dma_cap_mask_t *mask,
                                       dma_filter_fn fn, void *fn_param,
                                       struct device_node *np)
{
        struct dma_device *device, *_d;
        struct dma_chan *chan = NULL;

        /* Find a channel */
        mutex_lock(&dma_list_mutex);
        list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
                /* Finds a DMA controller with matching device node */
                if (np && device->dev->of_node && np != device->dev->of_node)
                        continue;

                chan = find_candidate(device, mask, fn, fn_param);
                if (!IS_ERR(chan))
                        break;

                chan = NULL;
        }
        mutex_unlock(&dma_list_mutex);

        pr_debug("%s: %s (%s)\n",
                 __func__,
                 chan ? "success" : "fail",
                 chan ? dma_chan_name(chan) : NULL);

        return chan;
}
EXPORT_SYMBOL_GPL(__dma_request_channel);

static const struct dma_slave_map *dma_filter_match(struct dma_device *device,
                                                    const char *name,
                                                    struct device *dev)
{
        int i;

        if (!device->filter.mapcnt)
                return NULL;

        for (i = 0; i < device->filter.mapcnt; i++) {
                const struct dma_slave_map *map = &device->filter.map[i];

                if (!strcmp(map->devname, dev_name(dev)) &&
                    !strcmp(map->slave, name))
                        return map;
        }

        return NULL;
}

/**
 * dma_request_chan - try to allocate an exclusive slave channel
 * @dev:        pointer to client device structure
 * @name:       slave channel name
 *
 * Returns pointer to appropriate DMA channel on success or an error pointer.
 */
struct dma_chan *dma_request_chan(struct device *dev, const char *name)
{
        struct dma_device *d, *_d;
        struct dma_chan *chan = NULL;

        /* If device-tree is present get slave info from here */
        if (dev->of_node)
                chan = of_dma_request_slave_channel(dev->of_node, name);

        /* If device was enumerated by ACPI get slave info from here */
        if (has_acpi_companion(dev) && !chan)
                chan = acpi_dma_request_slave_chan_by_name(dev, name);

        if (PTR_ERR(chan) == -EPROBE_DEFER)
                return chan;

        if (!IS_ERR_OR_NULL(chan))
                goto found;

        /* Try to find the channel via the DMA filter map(s) */
        mutex_lock(&dma_list_mutex);
        list_for_each_entry_safe(d, _d, &dma_device_list, global_node) {
                dma_cap_mask_t mask;
                const struct dma_slave_map *map = dma_filter_match(d, name, dev);

                if (!map)
                        continue;

                dma_cap_zero(mask);
                dma_cap_set(DMA_SLAVE, mask);

                chan = find_candidate(d, &mask, d->filter.fn, map->param);
                if (!IS_ERR(chan))
                        break;
        }
        mutex_unlock(&dma_list_mutex);

        if (IS_ERR_OR_NULL(chan))
                return chan ? chan : ERR_PTR(-EPROBE_DEFER);

found:
#ifdef CONFIG_DEBUG_FS
        chan->dbg_client_name = kasprintf(GFP_KERNEL, "%s:%s", dev_name(dev),
                                          name);
#endif

        chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
        if (!chan->name)
                return chan;
        chan->slave = dev;

        if (sysfs_create_link(&chan->dev->device.kobj, &dev->kobj,
                              DMA_SLAVE_NAME))
                dev_warn(dev, "Cannot create DMA %s symlink\n", DMA_SLAVE_NAME);
        if (sysfs_create_link(&dev->kobj, &chan->dev->device.kobj, chan->name))
                dev_warn(dev, "Cannot create DMA %s symlink\n", chan->name);

        return chan;
}
EXPORT_SYMBOL_GPL(dma_request_chan);

/**
 * dma_request_slave_channel - try to allocate an exclusive slave channel
 * @dev:        pointer to client device structure
 * @name:       slave channel name
 *
 * Returns pointer to appropriate DMA channel on success or NULL.
 */
struct dma_chan *dma_request_slave_channel(struct device *dev,
                                           const char *name)
{
        struct dma_chan *ch = dma_request_chan(dev, name);
        if (IS_ERR(ch))
                return NULL;

        return ch;
}
EXPORT_SYMBOL_GPL(dma_request_slave_channel);

/**
 * dma_request_chan_by_mask - allocate a channel satisfying certain capabilities
 * @mask: capabilities that the channel must satisfy
 *
 * Returns pointer to appropriate DMA channel on success or an error pointer.
 */
struct dma_chan *dma_request_chan_by_mask(const dma_cap_mask_t *mask)
{
        struct dma_chan *chan;

        if (!mask)
                return ERR_PTR(-ENODEV);

        chan = __dma_request_channel(mask, NULL, NULL, NULL);
        if (!chan) {
                mutex_lock(&dma_list_mutex);
                if (list_empty(&dma_device_list))
                        chan = ERR_PTR(-EPROBE_DEFER);
                else
                        chan = ERR_PTR(-ENODEV);
                mutex_unlock(&dma_list_mutex);
        }

        return chan;
}
EXPORT_SYMBOL_GPL(dma_request_chan_by_mask);

void dma_release_channel(struct dma_chan *chan)
{
        mutex_lock(&dma_list_mutex);
        WARN_ONCE(chan->client_count != 1,
                  "chan reference count %d != 1\n", chan->client_count);
        dma_chan_put(chan);
        /* drop PRIVATE cap enabled by __dma_request_channel() */
        if (--chan->device->privatecnt == 0)
                dma_cap_clear(DMA_PRIVATE, chan->device->cap_mask);

        if (chan->slave) {
                sysfs_remove_link(&chan->dev->device.kobj, DMA_SLAVE_NAME);
                sysfs_remove_link(&chan->slave->kobj, chan->name);
                kfree(chan->name);
                chan->name = NULL;
                chan->slave = NULL;
        }

#ifdef CONFIG_DEBUG_FS
        kfree(chan->dbg_client_name);
        chan->dbg_client_name = NULL;
#endif
        mutex_unlock(&dma_list_mutex);
}
EXPORT_SYMBOL_GPL(dma_release_channel);

/**
 * dmaengine_get - register interest in dma_channels
 */
void dmaengine_get(void)
{
        struct dma_device *device, *_d;
        struct dma_chan *chan;
        int err;

        mutex_lock(&dma_list_mutex);
        dmaengine_ref_count++;

        /* try to grab channels */
        list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
                        continue;
                list_for_each_entry(chan, &device->channels, device_node) {
                        err = dma_chan_get(chan);
                        if (err == -ENODEV) {
                                /* module removed before we could use it */
                                list_del_rcu(&device->global_node);
                                break;
                        } else if (err)
                                dev_dbg(chan->device->dev,
                                        "%s: failed to get %s: (%d)\n",
                                        __func__, dma_chan_name(chan), err);
                }
        }

        /* if this is the first reference and there were channels
         * waiting we need to rebalance to get those channels
         * incorporated into the channel table
         */
        if (dmaengine_ref_count == 1)
                dma_channel_rebalance();
        mutex_unlock(&dma_list_mutex);
}
EXPORT_SYMBOL(dmaengine_get);

/**
 * dmaengine_put - let dma drivers be removed when ref_count == 0
 */
void dmaengine_put(void)
{
        struct dma_device *device, *_d;
        struct dma_chan *chan;

        mutex_lock(&dma_list_mutex);
        dmaengine_ref_count--;
        BUG_ON(dmaengine_ref_count < 0);
        /* drop channel references */
        list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
                        continue;
                list_for_each_entry(chan, &device->channels, device_node)
                        dma_chan_put(chan);
        }
        mutex_unlock(&dma_list_mutex);
}
EXPORT_SYMBOL(dmaengine_put);

static bool device_has_all_tx_types(struct dma_device *device)
{
        /* A device that satisfies this test has channels that will never cause
         * an async_tx channel switch event as all possible operation types can
         * be handled.
         */
        #ifdef CONFIG_ASYNC_TX_DMA
        if (!dma_has_cap(DMA_INTERRUPT, device->cap_mask))
                return false;
        #endif

        #if IS_ENABLED(CONFIG_ASYNC_MEMCPY)
        if (!dma_has_cap(DMA_MEMCPY, device->cap_mask))
                return false;
        #endif

        #if IS_ENABLED(CONFIG_ASYNC_XOR)
        if (!dma_has_cap(DMA_XOR, device->cap_mask))
                return false;

        #ifndef CONFIG_ASYNC_TX_DISABLE_XOR_VAL_DMA
        if (!dma_has_cap(DMA_XOR_VAL, device->cap_mask))
                return false;
        #endif
        #endif

        #if IS_ENABLED(CONFIG_ASYNC_PQ)
        if (!dma_has_cap(DMA_PQ, device->cap_mask))
                return false;

        #ifndef CONFIG_ASYNC_TX_DISABLE_PQ_VAL_DMA
        if (!dma_has_cap(DMA_PQ_VAL, device->cap_mask))
                return false;
        #endif
        #endif

        return true;
}

static int get_dma_id(struct dma_device *device)
{
        int rc = ida_alloc(&dma_ida, GFP_KERNEL);

        if (rc < 0)
                return rc;
        device->dev_id = rc;
        return 0;
}

static int __dma_async_device_channel_register(struct dma_device *device,
                                               struct dma_chan *chan)
{
        int rc = 0;

        chan->local = alloc_percpu(typeof(*chan->local));
        if (!chan->local)
                goto err_out;
        chan->dev = kzalloc(sizeof(*chan->dev), GFP_KERNEL);
        if (!chan->dev) {
                free_percpu(chan->local);
                chan->local = NULL;
                goto err_out;
        }

        /*
         * When the chan_id is a negative value, we are dynamically adding
         * the channel. Otherwise we are static enumerating.
         */
        mutex_lock(&device->chan_mutex);
        chan->chan_id = ida_alloc(&device->chan_ida, GFP_KERNEL);
        mutex_unlock(&device->chan_mutex);
        if (chan->chan_id < 0) {
                pr_err("%s: unable to alloc ida for chan: %d\n",
                       __func__, chan->chan_id);
                goto err_out;
        }

        chan->dev->device.class = &dma_devclass;
        chan->dev->device.parent = device->dev;
        chan->dev->chan = chan;
        chan->dev->dev_id = device->dev_id;
        dev_set_name(&chan->dev->device, "dma%dchan%d",
                     device->dev_id, chan->chan_id);
        rc = device_register(&chan->dev->device);
        if (rc)
                goto err_out_ida;
        chan->client_count = 0;
        device->chancnt++;

        return 0;

 err_out_ida:
        mutex_lock(&device->chan_mutex);
        ida_free(&device->chan_ida, chan->chan_id);
        mutex_unlock(&device->chan_mutex);
 err_out:
        free_percpu(chan->local);
        kfree(chan->dev);
        return rc;
}

int dma_async_device_channel_register(struct dma_device *device,
                                      struct dma_chan *chan)
{
        int rc;

        rc = __dma_async_device_channel_register(device, chan);
        if (rc < 0)
                return rc;

        dma_channel_rebalance();
        return 0;
}
EXPORT_SYMBOL_GPL(dma_async_device_channel_register);

static void __dma_async_device_channel_unregister(struct dma_device *device,
                                                  struct dma_chan *chan)
{
        WARN_ONCE(!device->device_release && chan->client_count,
                  "%s called while %d clients hold a reference\n",
                  __func__, chan->client_count);
        mutex_lock(&dma_list_mutex);
        list_del(&chan->device_node);
        device->chancnt--;
        chan->dev->chan = NULL;
        mutex_unlock(&dma_list_mutex);
        mutex_lock(&device->chan_mutex);
        ida_free(&device->chan_ida, chan->chan_id);
        mutex_unlock(&device->chan_mutex);
        device_unregister(&chan->dev->device);
        free_percpu(chan->local);
}

void dma_async_device_channel_unregister(struct dma_device *device,
                                         struct dma_chan *chan)
{
        __dma_async_device_channel_unregister(device, chan);
        dma_channel_rebalance();
}
EXPORT_SYMBOL_GPL(dma_async_device_channel_unregister);

/**
 * dma_async_device_register - registers DMA devices found
 * @device: &dma_device
 *
 * After calling this routine the structure should not be freed except in the
 * device_release() callback which will be called after
 * dma_async_device_unregister() is called and no further references are taken.
 */
int dma_async_device_register(struct dma_device *device)
{
        int rc;
        struct dma_chan* chan;

        if (!device)
                return -ENODEV;

        /* validate device routines */
        if (!device->dev) {
                pr_err("DMAdevice must have dev\n");
                return -EIO;
        }

        device->owner = device->dev->driver->owner;

        if (dma_has_cap(DMA_MEMCPY, device->cap_mask) && !device->device_prep_dma_memcpy) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_MEMCPY");
                return -EIO;
        }

        if (dma_has_cap(DMA_XOR, device->cap_mask) && !device->device_prep_dma_xor) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_XOR");
                return -EIO;
        }

        if (dma_has_cap(DMA_XOR_VAL, device->cap_mask) && !device->device_prep_dma_xor_val) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_XOR_VAL");
                return -EIO;
        }

        if (dma_has_cap(DMA_PQ, device->cap_mask) && !device->device_prep_dma_pq) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_PQ");
                return -EIO;
        }

        if (dma_has_cap(DMA_PQ_VAL, device->cap_mask) && !device->device_prep_dma_pq_val) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_PQ_VAL");
                return -EIO;
        }

        if (dma_has_cap(DMA_MEMSET, device->cap_mask) && !device->device_prep_dma_memset) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_MEMSET");
                return -EIO;
        }

        if (dma_has_cap(DMA_INTERRUPT, device->cap_mask) && !device->device_prep_dma_interrupt) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_INTERRUPT");
                return -EIO;
        }

        if (dma_has_cap(DMA_CYCLIC, device->cap_mask) && !device->device_prep_dma_cyclic) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_CYCLIC");
                return -EIO;
        }

        if (dma_has_cap(DMA_INTERLEAVE, device->cap_mask) && !device->device_prep_interleaved_dma) {
                dev_err(device->dev,
                        "Device claims capability %s, but op is not defined\n",
                        "DMA_INTERLEAVE");
                return -EIO;
        }


        if (!device->device_tx_status) {
                dev_err(device->dev, "Device tx_status is not defined\n");
                return -EIO;
        }


        if (!device->device_issue_pending) {
                dev_err(device->dev, "Device issue_pending is not defined\n");
                return -EIO;
        }

        if (!device->device_release)
                dev_dbg(device->dev,
                         "WARN: Device release is not defined so it is not safe to unbind this driver while in use\n");

        kref_init(&device->ref);

        /* note: this only matters in the
         * CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH=n case
         */
        if (device_has_all_tx_types(device))
                dma_cap_set(DMA_ASYNC_TX, device->cap_mask);

        rc = get_dma_id(device);
        if (rc != 0)
                return rc;

        mutex_init(&device->chan_mutex);
        ida_init(&device->chan_ida);

        /* represent channels in sysfs. Probably want devs too */
        list_for_each_entry(chan, &device->channels, device_node) {
                rc = __dma_async_device_channel_register(device, chan);
                if (rc < 0)
                        goto err_out;
        }

        mutex_lock(&dma_list_mutex);
        /* take references on public channels */
        if (dmaengine_ref_count && !dma_has_cap(DMA_PRIVATE, device->cap_mask))
                list_for_each_entry(chan, &device->channels, device_node) {
                        /* if clients are already waiting for channels we need
                         * to take references on their behalf
                         */
                        if (dma_chan_get(chan) == -ENODEV) {
                                /* note we can only get here for the first
                                 * channel as the remaining channels are
                                 * guaranteed to get a reference
                                 */
                                rc = -ENODEV;
                                mutex_unlock(&dma_list_mutex);
                                goto err_out;
                        }
                }
        list_add_tail_rcu(&device->global_node, &dma_device_list);
        if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
                device->privatecnt++;   /* Always private */
        dma_channel_rebalance();
        mutex_unlock(&dma_list_mutex);

        dmaengine_debug_register(device);

        return 0;

err_out:
        /* if we never registered a channel just release the idr */
        if (!device->chancnt) {
                ida_free(&dma_ida, device->dev_id);
                return rc;
        }

        list_for_each_entry(chan, &device->channels, device_node) {
                if (chan->local == NULL)
                        continue;
                mutex_lock(&dma_list_mutex);
                chan->dev->chan = NULL;
                mutex_unlock(&dma_list_mutex);
                device_unregister(&chan->dev->device);
                free_percpu(chan->local);
        }
        return rc;
}
EXPORT_SYMBOL(dma_async_device_register);

/**
 * dma_async_device_unregister - unregister a DMA device
 * @device: &dma_device
 *
 * This routine is called by dma driver exit routines, dmaengine holds module
 * references to prevent it being called while channels are in use.
 */
void dma_async_device_unregister(struct dma_device *device)
{
        struct dma_chan *chan, *n;

        dmaengine_debug_unregister(device);

        list_for_each_entry_safe(chan, n, &device->channels, device_node)
                __dma_async_device_channel_unregister(device, chan);

        mutex_lock(&dma_list_mutex);
        /*
         * setting DMA_PRIVATE ensures the device being torn down will not
         * be used in the channel_table
         */
        dma_cap_set(DMA_PRIVATE, device->cap_mask);
        dma_channel_rebalance();
        ida_free(&dma_ida, device->dev_id);
        dma_device_put(device);
        mutex_unlock(&dma_list_mutex);
}
EXPORT_SYMBOL(dma_async_device_unregister);

static void dmam_device_release(struct device *dev, void *res)
{
        struct dma_device *device;

        device = *(struct dma_device **)res;
        dma_async_device_unregister(device);
}

/**
 * dmaenginem_async_device_register - registers DMA devices found
 * @device: &dma_device
 *
 * The operation is managed and will be undone on driver detach.
 */
int dmaenginem_async_device_register(struct dma_device *device)
{
        void *p;
        int ret;

        p = devres_alloc(dmam_device_release, sizeof(void *), GFP_KERNEL);
        if (!p)
                return -ENOMEM;

        ret = dma_async_device_register(device);
        if (!ret) {
                *(struct dma_device **)p = device;
                devres_add(device->dev, p);
        } else {
                devres_free(p);
        }

        return ret;
}
EXPORT_SYMBOL(dmaenginem_async_device_register);

struct dmaengine_unmap_pool {
        struct kmem_cache *cache;
        const char *name;
        mempool_t *pool;
        size_t size;
};

#define __UNMAP_POOL(x) { .size = x, .name = "dmaengine-unmap-" __stringify(x) }
static struct dmaengine_unmap_pool unmap_pool[] = {
        __UNMAP_POOL(2),
        #if IS_ENABLED(CONFIG_DMA_ENGINE_RAID)
        __UNMAP_POOL(16),
        __UNMAP_POOL(128),
        __UNMAP_POOL(256),
        #endif
};

static struct dmaengine_unmap_pool *__get_unmap_pool(int nr)
{
        int order = get_count_order(nr);

        switch (order) {
        case 0 ... 1:
                return &unmap_pool[0];
#if IS_ENABLED(CONFIG_DMA_ENGINE_RAID)
        case 2 ... 4:
                return &unmap_pool[1];
        case 5 ... 7:
                return &unmap_pool[2];
        case 8:
                return &unmap_pool[3];
#endif
        default:
                BUG();
                return NULL;
        }
}

static void dmaengine_unmap(struct kref *kref)
{
        struct dmaengine_unmap_data *unmap = container_of(kref, typeof(*unmap), kref);
        struct device *dev = unmap->dev;
        int cnt, i;

        cnt = unmap->to_cnt;
        for (i = 0; i < cnt; i++)
                dma_unmap_page(dev, unmap->addr[i], unmap->len,
                               DMA_TO_DEVICE);
        cnt += unmap->from_cnt;
        for (; i < cnt; i++)
                dma_unmap_page(dev, unmap->addr[i], unmap->len,
                               DMA_FROM_DEVICE);
        cnt += unmap->bidi_cnt;
        for (; i < cnt; i++) {
                if (unmap->addr[i] == 0)
                        continue;
                dma_unmap_page(dev, unmap->addr[i], unmap->len,
                               DMA_BIDIRECTIONAL);
        }
        cnt = unmap->map_cnt;
        mempool_free(unmap, __get_unmap_pool(cnt)->pool);
}

void dmaengine_unmap_put(struct dmaengine_unmap_data *unmap)
{
        if (unmap)
                kref_put(&unmap->kref, dmaengine_unmap);
}
EXPORT_SYMBOL_GPL(dmaengine_unmap_put);

static void dmaengine_destroy_unmap_pool(void)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(unmap_pool); i++) {
                struct dmaengine_unmap_pool *p = &unmap_pool[i];

                mempool_destroy(p->pool);
                p->pool = NULL;
                kmem_cache_destroy(p->cache);
                p->cache = NULL;
        }
}

static int __init dmaengine_init_unmap_pool(void)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(unmap_pool); i++) {
                struct dmaengine_unmap_pool *p = &unmap_pool[i];
                size_t size;

                size = sizeof(struct dmaengine_unmap_data) +
                       sizeof(dma_addr_t) * p->size;

                p->cache = kmem_cache_create(p->name, size, 0,
                                             SLAB_HWCACHE_ALIGN, NULL);
                if (!p->cache)
                        break;
                p->pool = mempool_create_slab_pool(1, p->cache);
                if (!p->pool)
                        break;
        }

        if (i == ARRAY_SIZE(unmap_pool))
                return 0;

        dmaengine_destroy_unmap_pool();
        return -ENOMEM;
}

struct dmaengine_unmap_data *
dmaengine_get_unmap_data(struct device *dev, int nr, gfp_t flags)
{
        struct dmaengine_unmap_data *unmap;

        unmap = mempool_alloc(__get_unmap_pool(nr)->pool, flags);
        if (!unmap)
                return NULL;

        memset(unmap, 0, sizeof(*unmap));
        kref_init(&unmap->kref);
        unmap->dev = dev;
        unmap->map_cnt = nr;

        return unmap;
}
EXPORT_SYMBOL(dmaengine_get_unmap_data);

void dma_async_tx_descriptor_init(struct dma_async_tx_descriptor *tx,
        struct dma_chan *chan)
{
        tx->chan = chan;
        #ifdef CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH
        spin_lock_init(&tx->lock);
        #endif
}
EXPORT_SYMBOL(dma_async_tx_descriptor_init);

static inline int desc_check_and_set_metadata_mode(
        struct dma_async_tx_descriptor *desc, enum dma_desc_metadata_mode mode)
{
        /* Make sure that the metadata mode is not mixed */
        if (!desc->desc_metadata_mode) {
                if (dmaengine_is_metadata_mode_supported(desc->chan, mode))
                        desc->desc_metadata_mode = mode;
                else
                        return -ENOTSUPP;
        } else if (desc->desc_metadata_mode != mode) {
                return -EINVAL;
        }

        return 0;
}

int dmaengine_desc_attach_metadata(struct dma_async_tx_descriptor *desc,
                                   void *data, size_t len)
{
        int ret;

        if (!desc)
                return -EINVAL;

        ret = desc_check_and_set_metadata_mode(desc, DESC_METADATA_CLIENT);
        if (ret)
                return ret;

        if (!desc->metadata_ops || !desc->metadata_ops->attach)
                return -ENOTSUPP;

        return desc->metadata_ops->attach(desc, data, len);
}
EXPORT_SYMBOL_GPL(dmaengine_desc_attach_metadata);

void *dmaengine_desc_get_metadata_ptr(struct dma_async_tx_descriptor *desc,
                                      size_t *payload_len, size_t *max_len)
{
        int ret;

        if (!desc)
                return ERR_PTR(-EINVAL);

        ret = desc_check_and_set_metadata_mode(desc, DESC_METADATA_ENGINE);
        if (ret)
                return ERR_PTR(ret);

        if (!desc->metadata_ops || !desc->metadata_ops->get_ptr)
                return ERR_PTR(-ENOTSUPP);

        return desc->metadata_ops->get_ptr(desc, payload_len, max_len);
}
EXPORT_SYMBOL_GPL(dmaengine_desc_get_metadata_ptr);

int dmaengine_desc_set_metadata_len(struct dma_async_tx_descriptor *desc,
                                    size_t payload_len)
{
        int ret;

        if (!desc)
                return -EINVAL;

        ret = desc_check_and_set_metadata_mode(desc, DESC_METADATA_ENGINE);
        if (ret)
                return ret;

        if (!desc->metadata_ops || !desc->metadata_ops->set_len)
                return -ENOTSUPP;

        return desc->metadata_ops->set_len(desc, payload_len);
}
EXPORT_SYMBOL_GPL(dmaengine_desc_set_metadata_len);

/* dma_wait_for_async_tx - spin wait for a transaction to complete
 * @tx: in-flight transaction to wait on
 */
enum dma_status
dma_wait_for_async_tx(struct dma_async_tx_descriptor *tx)
{
        unsigned long dma_sync_wait_timeout = jiffies + msecs_to_jiffies(5000);

        if (!tx)
                return DMA_COMPLETE;

        while (tx->cookie == -EBUSY) {
                if (time_after_eq(jiffies, dma_sync_wait_timeout)) {
                        dev_err(tx->chan->device->dev,
                                "%s timeout waiting for descriptor submission\n",
                                __func__);
                        return DMA_ERROR;
                }
                cpu_relax();
        }
        return dma_sync_wait(tx->chan, tx->cookie);
}
EXPORT_SYMBOL_GPL(dma_wait_for_async_tx);

/* dma_run_dependencies - helper routine for dma drivers to process
 *      (start) dependent operations on their target channel
 * @tx: transaction with dependencies
 */
void dma_run_dependencies(struct dma_async_tx_descriptor *tx)
{
        struct dma_async_tx_descriptor *dep = txd_next(tx);
        struct dma_async_tx_descriptor *dep_next;
        struct dma_chan *chan;

        if (!dep)
                return;

        /* we'll submit tx->next now, so clear the link */
        txd_clear_next(tx);
        chan = dep->chan;

        /* keep submitting up until a channel switch is detected
         * in that case we will be called again as a result of
         * processing the interrupt from async_tx_channel_switch
         */
        for (; dep; dep = dep_next) {
                txd_lock(dep);
                txd_clear_parent(dep);
                dep_next = txd_next(dep);
                if (dep_next && dep_next->chan == chan)
                        txd_clear_next(dep); /* ->next will be submitted */
                else
                        dep_next = NULL; /* submit current dep and terminate */
                txd_unlock(dep);

                dep->tx_submit(dep);
        }

        chan->device->device_issue_pending(chan);
}
EXPORT_SYMBOL_GPL(dma_run_dependencies);

static int __init dma_bus_init(void)
{
        int err = dmaengine_init_unmap_pool();

        if (err)
                return err;

        err = class_register(&dma_devclass);
        if (!err)
                dmaengine_debugfs_init();

        return err;
}
arch_initcall(dma_bus_init);