dmaengine: centralize channel allocation, introduce dma_find_channel

Allowing multiple clients to each define their own channel allocation
scheme quickly leads to a pathological situation.  For memory-to-memory
offload all clients can share a central allocator.

This simply moves the existing async_tx allocator to dmaengine with
minimal fixups:
* async_tx.c:get_chan_ref_by_cap --> dmaengine.c:nth_chan
* async_tx.c:async_tx_rebalance --> dmaengine.c:dma_channel_rebalance
* split out common code from async_tx.c:__async_tx_find_channel -->
  dma_find_channel

Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

3 files changed, 174 insertions, 143 deletions

diff --git a/crypto/async_tx/async_tx.c b/crypto/async_tx/async_tx.c
index 43fe4cbe71e6..b88bb1f608fc 100644
--- a/crypto/async_tx/async_tx.c
+++ b/crypto/async_tx/async_tx.c
@@ -38,25 +38,10 @@ static struct dma_client async_tx_dma = {
 };
 
 /**
- * dma_cap_mask_all - enable iteration over all operation types
- */
-static dma_cap_mask_t dma_cap_mask_all;
-
-/**
- * chan_ref_percpu - tracks channel allocations per core/opertion
- */
-struct chan_ref_percpu {
-        struct dma_chan_ref *ref;
-};
-
-static int channel_table_initialized;
-static struct chan_ref_percpu *channel_table[DMA_TX_TYPE_END];
-
-/**
  * async_tx_lock - protect modification of async_tx_master_list and serialize
  *      rebalance operations
  */
-static spinlock_t async_tx_lock;
+static DEFINE_SPINLOCK(async_tx_lock);
 
 static LIST_HEAD(async_tx_master_list);
 
@@ -89,85 +74,6 @@ init_dma_chan_ref(struct dma_chan_ref *ref, struct dma_chan *chan)
         atomic_set(&ref->count, 0);
 }
 
-/**
- * get_chan_ref_by_cap - returns the nth channel of the given capability
- *      defaults to returning the channel with the desired capability and the
- *      lowest reference count if the index can not be satisfied
- * @cap: capability to match
- * @index: nth channel desired, passing -1 has the effect of forcing the
- *  default return value
- */
-static struct dma_chan_ref *
-get_chan_ref_by_cap(enum dma_transaction_type cap, int index)
-{
-        struct dma_chan_ref *ret_ref = NULL, *min_ref = NULL, *ref;
-
-        rcu_read_lock();
-        list_for_each_entry_rcu(ref, &async_tx_master_list, node)
-                if (dma_has_cap(cap, ref->chan->device->cap_mask)) {
-                        if (!min_ref)
-                                min_ref = ref;
-                        else if (atomic_read(&ref->count) <
-                                atomic_read(&min_ref->count))
-                                min_ref = ref;
-
-                        if (index-- == 0) {
-                                ret_ref = ref;
-                                break;
-                        }
-                }
-        rcu_read_unlock();
-
-        if (!ret_ref)
-                ret_ref = min_ref;
-
-        if (ret_ref)
-                atomic_inc(&ret_ref->count);
-
-        return ret_ref;
-}
-
-/**
- * async_tx_rebalance - redistribute the available channels, optimize
- * for cpu isolation in the SMP case, and opertaion isolation in the
- * uniprocessor case
- */
-static void async_tx_rebalance(void)
-{
-        int cpu, cap, cpu_idx = 0;
-        unsigned long flags;
-
-        if (!channel_table_initialized)
-                return;
-
-        spin_lock_irqsave(&async_tx_lock, flags);
-
-        /* undo the last distribution */
-        for_each_dma_cap_mask(cap, dma_cap_mask_all)
-                for_each_possible_cpu(cpu) {
-                        struct dma_chan_ref *ref =
-                                per_cpu_ptr(channel_table[cap], cpu)->ref;
-                        if (ref) {
-                                atomic_set(&ref->count, 0);
-                                per_cpu_ptr(channel_table[cap], cpu)->ref =
-                                                                        NULL;
-                        }
-                }
-
-        for_each_dma_cap_mask(cap, dma_cap_mask_all)
-                for_each_online_cpu(cpu) {
-                        struct dma_chan_ref *new;
-                        if (NR_CPUS > 1)
-                                new = get_chan_ref_by_cap(cap, cpu_idx++);
-                        else
-                                new = get_chan_ref_by_cap(cap, -1);
-
-                        per_cpu_ptr(channel_table[cap], cpu)->ref = new;
-                }
-
-        spin_unlock_irqrestore(&async_tx_lock, flags);
-}
-
 static enum dma_state_client
 dma_channel_add_remove(struct dma_client *client,
         struct dma_chan *chan, enum dma_state state)
@@ -211,8 +117,6 @@ dma_channel_add_remove(struct dma_client *client,
                                 " (-ENOMEM)\n");
                         return 0;
                 }
-
-                async_tx_rebalance();
                 break;
         case DMA_RESOURCE_REMOVED:
                 found = 0;
@@ -233,8 +137,6 @@ dma_channel_add_remove(struct dma_client *client,
                         ack = DMA_ACK;
                 else
                         break;
-
-                async_tx_rebalance();
                 break;
         case DMA_RESOURCE_SUSPEND:
         case DMA_RESOURCE_RESUME:
@@ -248,51 +150,18 @@ dma_channel_add_remove(struct dma_client *client,
         return ack;
 }
 
-static int __init
-async_tx_init(void)
+static int __init async_tx_init(void)
 {
-        enum dma_transaction_type cap;
-
-        spin_lock_init(&async_tx_lock);
-        bitmap_fill(dma_cap_mask_all.bits, DMA_TX_TYPE_END);
-
-        /* an interrupt will never be an explicit operation type.
-         * clearing this bit prevents allocation to a slot in 'channel_table'
-         */
-        clear_bit(DMA_INTERRUPT, dma_cap_mask_all.bits);
-
-        for_each_dma_cap_mask(cap, dma_cap_mask_all) {
-                channel_table[cap] = alloc_percpu(struct chan_ref_percpu);
-                if (!channel_table[cap])
-                        goto err;
-        }
-
-        channel_table_initialized = 1;
         dma_async_client_register(&async_tx_dma);
         dma_async_client_chan_request(&async_tx_dma);
 
         printk(KERN_INFO "async_tx: api initialized (async)\n");
 
         return 0;
-err:
-        printk(KERN_ERR "async_tx: initialization failure\n");
-
-        while (--cap >= 0)
-                free_percpu(channel_table[cap]);
-
-        return 1;
 }
 
 static void __exit async_tx_exit(void)
 {
-        enum dma_transaction_type cap;
-
-        channel_table_initialized = 0;
-
-        for_each_dma_cap_mask(cap, dma_cap_mask_all)
-                if (channel_table[cap])
-                        free_percpu(channel_table[cap]);
-
         dma_async_client_unregister(&async_tx_dma);
 }
 
@@ -308,16 +177,9 @@ __async_tx_find_channel(struct dma_async_tx_descriptor *depend_tx,
 {
         /* see if we can keep the chain on one channel */
         if (depend_tx &&
-                dma_has_cap(tx_type, depend_tx->chan->device->cap_mask))
+            dma_has_cap(tx_type, depend_tx->chan->device->cap_mask))
                 return depend_tx->chan;
-        else if (likely(channel_table_initialized)) {
-                struct dma_chan_ref *ref;
-                int cpu = get_cpu();
-                ref = per_cpu_ptr(channel_table[tx_type], cpu)->ref;
-                put_cpu();
-                return ref ? ref->chan : NULL;
-        } else
-                return NULL;
+        return dma_find_channel(tx_type);
 }
 EXPORT_SYMBOL_GPL(__async_tx_find_channel);
 #else
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index d4d925912c47..87a8cd4791ed 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -295,6 +295,164 @@ static void dma_chan_release(struct dma_chan *chan)
 }
 
 /**
+ * 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 *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' 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_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: initialization failure\n");
+                for_each_dma_cap_mask(cap, dma_cap_mask_all)
+                        if (channel_table[cap])
+                                free_percpu(channel_table[cap]);
+        }
+
+        return err;
+}
+subsys_initcall(dma_channel_table_init);
+
+/**
+ * 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)
+{
+        struct dma_chan *chan;
+        int cpu;
+
+        WARN_ONCE(dmaengine_ref_count == 0,
+                  "client called %s without a reference", __func__);
+
+        cpu = get_cpu();
+        chan = per_cpu_ptr(channel_table[tx_type], cpu)->chan;
+        put_cpu();
+
+        return chan;
+}
+EXPORT_SYMBOL(dma_find_channel);
+
+/**
+ * nth_chan - returns the nth channel of the given capability
+ * @cap: capability to match
+ * @n: nth channel desired
+ *
+ * Defaults to returning the channel with the desired capability and the
+ * lowest reference count when 'n' cannot be satisfied.  Must be called
+ * under dma_list_mutex.
+ */
+static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n)
+{
+        struct dma_device *device;
+        struct dma_chan *chan;
+        struct dma_chan *ret = NULL;
+        struct dma_chan *min = NULL;
+
+        list_for_each_entry(device, &dma_device_list, global_node) {
+                if (!dma_has_cap(cap, device->cap_mask))
+                        continue;
+                list_for_each_entry(chan, &device->channels, device_node) {
+                        if (!chan->client_count)
+                                continue;
+                        if (!min)
+                                min = chan;
+                        else if (chan->table_count < min->table_count)
+                                min = chan;
+
+                        if (n-- == 0) {
+                                ret = chan;
+                                break; /* done */
+                        }
+                }
+                if (ret)
+                        break; /* done */
+        }
+
+        if (!ret)
+                ret = min;
+
+        if (ret)
+                ret->table_count++;
+
+        return ret;
+}
+
+/**
+ * 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;
+        int n;
+
+        /* 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)
+                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 */
+        n = 0;
+        for_each_dma_cap_mask(cap, dma_cap_mask_all)
+                for_each_online_cpu(cpu) {
+                        if (num_possible_cpus() > 1)
+                                chan = nth_chan(cap, n++);
+                        else
+                                chan = nth_chan(cap, -1);
+
+                        per_cpu_ptr(channel_table[cap], cpu)->chan = chan;
+                }
+}
+
+/**
  * dma_chans_notify_available - broadcast available channels to the clients
  */
 static void dma_clients_notify_available(void)
@@ -339,7 +497,12 @@ void dma_async_client_register(struct dma_client *client)
                                        dev_name(&chan->dev), 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();
         list_add_tail(&client->global_node, &dma_client_list);
         mutex_unlock(&dma_list_mutex);
 }
@@ -473,6 +636,7 @@ int dma_async_device_register(struct dma_device *device)
                         }
                 }
         list_add_tail(&device->global_node, &dma_device_list);
+        dma_channel_rebalance();
         mutex_unlock(&dma_list_mutex);
 
         dma_clients_notify_available();
@@ -514,6 +678,7 @@ void dma_async_device_unregister(struct dma_device *device)
 
         mutex_lock(&dma_list_mutex);
         list_del(&device->global_node);
+        dma_channel_rebalance();
         mutex_unlock(&dma_list_mutex);
 
         list_for_each_entry(chan, &device->channels, device_node) {
@@ -768,3 +933,4 @@ static int __init dma_bus_init(void)
 }
 subsys_initcall(dma_bus_init);
 
+
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index d18d37d1015d..b466f02e2433 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -182,6 +182,7 @@ struct dma_chan_percpu {
  * @device_node: used to add this to the device chan list
  * @local: per-cpu pointer to a struct dma_chan_percpu
  * @client-count: how many clients are using this channel
+ * @table_count: number of appearances in the mem-to-mem allocation table
  */
 struct dma_chan {
         struct dma_device *device;
@@ -198,6 +199,7 @@ struct dma_chan {
         struct list_head device_node;
         struct dma_chan_percpu *local;
         int client_count;
+        int table_count;
 };
 
 #define to_dma_chan(p) container_of(p, struct dma_chan, dev)
@@ -468,6 +470,7 @@ static inline enum dma_status dma_wait_for_async_tx(struct dma_async_tx_descript
 int dma_async_device_register(struct dma_device *device);
 void dma_async_device_unregister(struct dma_device *device);
 void dma_run_dependencies(struct dma_async_tx_descriptor *tx);
+struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type);
 
 /* --- Helper iov-locking functions --- */