dmaengine: remove 'bigref' infrastructure

Reference counting is done at the module level so clients need not worry
that a channel will leave while they are actively using dmaengine.

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

4 files changed, 9 insertions, 87 deletions

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 9fc91f973a9a..b245c38dbec3 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -34,26 +34,15 @@
  * 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.
  *
- * Each device has a kref, which is initialized to 1 when the device is
- * registered. A kref_get is done for each device registered.  When the
- * device is released, the corresponding kref_put is done in the release
- * method. Every time one of the device's channels is allocated to a client,
- * a kref_get occurs.  When the channel is freed, the corresponding kref_put
- * happens. The device's release function does a completion, so
- * unregister_device does a remove event, device_unregister, a kref_put
- * for the first reference, then waits on the completion for all other
- * references to finish.
- *
- * Each channel has an open-coded implementation of Rusty Russell's "bigref,"
- * with a kref and a per_cpu local_t.  A dma_chan_get is called when a client
- * signals that it wants to use a channel, and dma_chan_put is called when
- * a channel is removed or a client using it is unregistered.  A client can
- * take extra references per outstanding transaction, as is the case with
- * the NET DMA client.  The release function does a kref_put on the device.
- *      -ChrisL, DanW
+ * See Documentation/dmaengine.txt for more details
  */
 
 #include <linux/init.h>
@@ -114,18 +103,9 @@ static struct device_attribute dma_attrs[] = {
         __ATTR_NULL
 };
 
-static void dma_async_device_cleanup(struct kref *kref);
-
-static void dma_dev_release(struct device *dev)
-{
-        struct dma_chan *chan = to_dma_chan(dev);
-        kref_put(&chan->device->refcount, dma_async_device_cleanup);
-}
-
 static struct class dma_devclass = {
         .name           = "dma",
         .dev_attrs      = dma_attrs,
-        .dev_release    = dma_dev_release,
 };
 
 /* --- client and device registration --- */
@@ -233,29 +213,6 @@ enum dma_status dma_sync_wait(struct dma_chan *chan, dma_cookie_t cookie)
 EXPORT_SYMBOL(dma_sync_wait);
 
 /**
- * dma_chan_cleanup - release a DMA channel's resources
- * @kref: kernel reference structure that contains the DMA channel device
- */
-void dma_chan_cleanup(struct kref *kref)
-{
-        struct dma_chan *chan = container_of(kref, struct dma_chan, refcount);
-        kref_put(&chan->device->refcount, dma_async_device_cleanup);
-}
-EXPORT_SYMBOL(dma_chan_cleanup);
-
-static void dma_chan_free_rcu(struct rcu_head *rcu)
-{
-        struct dma_chan *chan = container_of(rcu, struct dma_chan, rcu);
-
-        kref_put(&chan->refcount, dma_chan_cleanup);
-}
-
-static void dma_chan_release(struct dma_chan *chan)
-{
-        call_rcu(&chan->rcu, dma_chan_free_rcu);
-}
-
-/**
  * dma_cap_mask_all - enable iteration over all operation types
  */
 static dma_cap_mask_t dma_cap_mask_all;
@@ -641,9 +598,6 @@ int dma_async_device_register(struct dma_device *device)
         BUG_ON(!device->device_issue_pending);
         BUG_ON(!device->dev);
 
-        init_completion(&device->done);
-        kref_init(&device->refcount);
-
         mutex_lock(&dma_list_mutex);
         device->dev_id = id++;
         mutex_unlock(&dma_list_mutex);
@@ -662,19 +616,11 @@ int dma_async_device_register(struct dma_device *device)
 
                 rc = device_register(&chan->dev);
                 if (rc) {
-                        chancnt--;
                         free_percpu(chan->local);
                         chan->local = NULL;
                         goto err_out;
                 }
-
-                /* One for the channel, one of the class device */
-                kref_get(&device->refcount);
-                kref_get(&device->refcount);
-                kref_init(&chan->refcount);
                 chan->client_count = 0;
-                chan->slow_ref = 0;
-                INIT_RCU_HEAD(&chan->rcu);
         }
         device->chancnt = chancnt;
 
@@ -705,9 +651,7 @@ err_out:
         list_for_each_entry(chan, &device->channels, device_node) {
                 if (chan->local == NULL)
                         continue;
-                kref_put(&device->refcount, dma_async_device_cleanup);
                 device_unregister(&chan->dev);
-                chancnt--;
                 free_percpu(chan->local);
         }
         return rc;
@@ -715,20 +659,11 @@ err_out:
 EXPORT_SYMBOL(dma_async_device_register);
 
 /**
- * dma_async_device_cleanup - function called when all references are released
- * @kref: kernel reference object
- */
-static void dma_async_device_cleanup(struct kref *kref)
-{
-        struct dma_device *device;
-
-        device = container_of(kref, struct dma_device, refcount);
-        complete(&device->done);
-}
-
-/**
  * 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)
 {
@@ -744,11 +679,7 @@ void dma_async_device_unregister(struct dma_device *device)
                           "%s called while %d clients hold a reference\n",
                           __func__, chan->client_count);
                 device_unregister(&chan->dev);
-                dma_chan_release(chan);
         }
-
-        kref_put(&device->refcount, dma_async_device_cleanup);
-        wait_for_completion(&device->done);
 }
 EXPORT_SYMBOL(dma_async_device_unregister);
 
diff --git a/drivers/dma/iop-adma.c b/drivers/dma/iop-adma.c
index c74ac9eb009a..df0e37d70b31 100644
--- a/drivers/dma/iop-adma.c
+++ b/drivers/dma/iop-adma.c
@@ -1253,7 +1253,6 @@ static int __devinit iop_adma_probe(struct platform_device *pdev)
         spin_lock_init(&iop_chan->lock);
         INIT_LIST_HEAD(&iop_chan->chain);
         INIT_LIST_HEAD(&iop_chan->all_slots);
-        INIT_RCU_HEAD(&iop_chan->common.rcu);
         iop_chan->common.device = dma_dev;
         list_add_tail(&iop_chan->common.device_node, &dma_dev->channels);
 
diff --git a/drivers/dma/mv_xor.c b/drivers/dma/mv_xor.c
index fbaa2f6225e2..d35cbd1ff0b3 100644
--- a/drivers/dma/mv_xor.c
+++ b/drivers/dma/mv_xor.c
@@ -1219,7 +1219,6 @@ static int __devinit mv_xor_probe(struct platform_device *pdev)
         INIT_LIST_HEAD(&mv_chan->chain);
         INIT_LIST_HEAD(&mv_chan->completed_slots);
         INIT_LIST_HEAD(&mv_chan->all_slots);
-        INIT_RCU_HEAD(&mv_chan->common.rcu);
         mv_chan->common.device = dma_dev;
 
         list_add_tail(&mv_chan->common.device_node, &dma_dev->channels);
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index db050e97d2b4..bca2fc758894 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -142,10 +142,6 @@ struct dma_chan {
         int chan_id;
         struct device dev;
 
-        struct kref refcount;
-        int slow_ref;
-        struct rcu_head rcu;
-
         struct list_head device_node;
         struct dma_chan_percpu *local;
         int client_count;
@@ -233,9 +229,6 @@ struct dma_device {
         dma_cap_mask_t  cap_mask;
         int max_xor;
 
-        struct kref refcount;
-        struct completion done;
-
         int dev_id;
         struct device *dev;