From f27c580c3628d79b17f38976d842a6d7f3616e2e Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Tue, 6 Jan 2009 11:38:18 -0700 Subject: 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 Signed-off-by: Dan Williams --- drivers/dma/dmaengine.c | 87 +++++-------------------------------------------- 1 file changed, 9 insertions(+), 78 deletions(-) (limited to 'drivers/dma/dmaengine.c') 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 @@ -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 --- */ @@ -232,29 +212,6 @@ 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 */ @@ -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; @@ -705,30 +651,19 @@ 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; } 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); -- cgit v1.2.3