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>
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 9fc91f9..b245c38 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 @@
__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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
"%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);