dmaengine: make clients responsible for managing channels
The current implementation assumes that a channel will only be used by one
client at a time. In order to enable channel sharing the dmaengine core is
changed to a model where clients subscribe to channel-available-events.
Instead of tracking how many channels a client wants and how many it has
received the core just broadcasts the available channels and lets the
clients optionally take a reference. The core learns about the clients'
needs at dma_event_callback time.
In support of multiple operation types, clients can specify a capability
mask to only be notified of channels that satisfy a certain set of
capabilities.
Changelog:
* removed DMA_TX_ARRAY_INIT, no longer needed
* dma_client_chan_free -> dma_chan_release: switch to global reference
counting only at device unregistration time, before it was also happening
at client unregistration time
* clients now return dma_state_client to dmaengine (ack, dup, nak)
* checkpatch.pl fixes
* fixup merge with git-ioat
Cc: Chris Leech <christopher.leech@intel.com>
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 404cc7b..8248992 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -37,11 +37,11 @@
* 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 client has a channels list, it's only modified under the client->lock
- * and in an RCU callback, so it's safe to read under rcu_read_lock().
+ * Each client is responsible for keeping track of the channels it uses. See
+ * the definition of dma_event_callback in dmaengine.h.
*
* Each device has a kref, which is initialized to 1 when the device is
- * registered. A kref_put is done for each class_device registered. When the
+ * registered. A kref_get is done for each class_device registered. When the
* class_device is released, the coresponding 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 coresponding kref_put
@@ -51,10 +51,12 @@
* 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 single reference is set when on an
- * ADDED event, and removed with a REMOVE event. Net DMA client takes an
- * extra reference per outstanding transaction. The relase function does a
- * kref_put on the device. -ChrisL
+ * 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 unregesitered. 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
*/
#include <linux/init.h>
@@ -102,8 +104,19 @@
static ssize_t show_in_use(struct class_device *cd, char *buf)
{
struct dma_chan *chan = container_of(cd, struct dma_chan, class_dev);
+ int in_use = 0;
- return sprintf(buf, "%d\n", (chan->client ? 1 : 0));
+ if (unlikely(chan->slow_ref) &&
+ atomic_read(&chan->refcount.refcount) > 1)
+ in_use = 1;
+ else {
+ if (local_read(&(per_cpu_ptr(chan->local,
+ get_cpu())->refcount)) > 0)
+ in_use = 1;
+ put_cpu();
+ }
+
+ return sprintf(buf, "%d\n", in_use);
}
static struct class_device_attribute dma_class_attrs[] = {
@@ -129,42 +142,53 @@
/* --- client and device registration --- */
+#define dma_chan_satisfies_mask(chan, mask) \
+ __dma_chan_satisfies_mask((chan), &(mask))
+static int
+__dma_chan_satisfies_mask(struct dma_chan *chan, dma_cap_mask_t *want)
+{
+ dma_cap_mask_t has;
+
+ bitmap_and(has.bits, want->bits, chan->device->cap_mask.bits,
+ DMA_TX_TYPE_END);
+ return bitmap_equal(want->bits, has.bits, DMA_TX_TYPE_END);
+}
+
/**
- * dma_client_chan_alloc - try to allocate a channel to a client
+ * dma_client_chan_alloc - try to allocate channels to a client
* @client: &dma_client
*
* Called with dma_list_mutex held.
*/
-static struct dma_chan *dma_client_chan_alloc(struct dma_client *client)
+static void dma_client_chan_alloc(struct dma_client *client)
{
struct dma_device *device;
struct dma_chan *chan;
- unsigned long flags;
int desc; /* allocated descriptor count */
+ enum dma_state_client ack;
- /* Find a channel, any DMA engine will do */
- list_for_each_entry(device, &dma_device_list, global_node) {
+ /* Find a channel */
+ list_for_each_entry(device, &dma_device_list, global_node)
list_for_each_entry(chan, &device->channels, device_node) {
- if (chan->client)
+ if (!dma_chan_satisfies_mask(chan, client->cap_mask))
continue;
desc = chan->device->device_alloc_chan_resources(chan);
if (desc >= 0) {
- kref_get(&device->refcount);
- kref_init(&chan->refcount);
- chan->slow_ref = 0;
- INIT_RCU_HEAD(&chan->rcu);
- chan->client = client;
- spin_lock_irqsave(&client->lock, flags);
- list_add_tail_rcu(&chan->client_node,
- &client->channels);
- spin_unlock_irqrestore(&client->lock, flags);
- return chan;
+ ack = client->event_callback(client,
+ chan,
+ DMA_RESOURCE_AVAILABLE);
+
+ /* we are done once this client rejects
+ * an available resource
+ */
+ if (ack == DMA_ACK) {
+ dma_chan_get(chan);
+ kref_get(&device->refcount);
+ } else if (ack == DMA_NAK)
+ return;
}
}
- }
-
- return NULL;
}
enum dma_status dma_sync_wait(struct dma_chan *chan, dma_cookie_t cookie)
@@ -193,7 +217,6 @@
{
struct dma_chan *chan = container_of(kref, struct dma_chan, refcount);
chan->device->device_free_chan_resources(chan);
- chan->client = NULL;
kref_put(&chan->device->refcount, dma_async_device_cleanup);
}
EXPORT_SYMBOL(dma_chan_cleanup);
@@ -209,7 +232,7 @@
kref_put(&chan->refcount, dma_chan_cleanup);
}
-static void dma_client_chan_free(struct dma_chan *chan)
+static void dma_chan_release(struct dma_chan *chan)
{
atomic_add(0x7FFFFFFF, &chan->refcount.refcount);
chan->slow_ref = 1;
@@ -217,41 +240,42 @@
}
/**
- * dma_chans_rebalance - reallocate channels to clients
- *
- * When the number of DMA channel in the system changes,
- * channels need to be rebalanced among clients.
+ * dma_chans_notify_available - broadcast available channels to the clients
*/
-static void dma_chans_rebalance(void)
+static void dma_clients_notify_available(void)
{
struct dma_client *client;
- struct dma_chan *chan;
- unsigned long flags;
+
+ mutex_lock(&dma_list_mutex);
+
+ list_for_each_entry(client, &dma_client_list, global_node)
+ dma_client_chan_alloc(client);
+
+ mutex_unlock(&dma_list_mutex);
+}
+
+/**
+ * dma_chans_notify_available - tell the clients that a channel is going away
+ * @chan: channel on its way out
+ */
+static void dma_clients_notify_removed(struct dma_chan *chan)
+{
+ struct dma_client *client;
+ enum dma_state_client ack;
mutex_lock(&dma_list_mutex);
list_for_each_entry(client, &dma_client_list, global_node) {
- while (client->chans_desired > client->chan_count) {
- chan = dma_client_chan_alloc(client);
- if (!chan)
- break;
- client->chan_count++;
- client->event_callback(client,
- chan,
- DMA_RESOURCE_ADDED);
- }
- while (client->chans_desired < client->chan_count) {
- spin_lock_irqsave(&client->lock, flags);
- chan = list_entry(client->channels.next,
- struct dma_chan,
- client_node);
- list_del_rcu(&chan->client_node);
- spin_unlock_irqrestore(&client->lock, flags);
- client->chan_count--;
- client->event_callback(client,
- chan,
- DMA_RESOURCE_REMOVED);
- dma_client_chan_free(chan);
+ ack = client->event_callback(client, chan,
+ DMA_RESOURCE_REMOVED);
+
+ /* client was holding resources for this channel so
+ * free it
+ */
+ if (ack == DMA_ACK) {
+ dma_chan_put(chan);
+ kref_put(&chan->device->refcount,
+ dma_async_device_cleanup);
}
}
@@ -259,28 +283,14 @@
}
/**
- * dma_async_client_register - allocate and register a &dma_client
- * @event_callback: callback for notification of channel addition/removal
+ * dma_async_client_register - register a &dma_client
+ * @client: ptr to a client structure with valid 'event_callback' and 'cap_mask'
*/
-struct dma_client *dma_async_client_register(dma_event_callback event_callback)
+void dma_async_client_register(struct dma_client *client)
{
- struct dma_client *client;
-
- client = kzalloc(sizeof(*client), GFP_KERNEL);
- if (!client)
- return NULL;
-
- INIT_LIST_HEAD(&client->channels);
- spin_lock_init(&client->lock);
- client->chans_desired = 0;
- client->chan_count = 0;
- client->event_callback = event_callback;
-
mutex_lock(&dma_list_mutex);
list_add_tail(&client->global_node, &dma_client_list);
mutex_unlock(&dma_list_mutex);
-
- return client;
}
EXPORT_SYMBOL(dma_async_client_register);
@@ -292,40 +302,42 @@
*/
void dma_async_client_unregister(struct dma_client *client)
{
+ struct dma_device *device;
struct dma_chan *chan;
+ enum dma_state_client ack;
if (!client)
return;
- rcu_read_lock();
- list_for_each_entry_rcu(chan, &client->channels, client_node)
- dma_client_chan_free(chan);
- rcu_read_unlock();
-
mutex_lock(&dma_list_mutex);
+ /* free all channels the client is holding */
+ list_for_each_entry(device, &dma_device_list, global_node)
+ list_for_each_entry(chan, &device->channels, device_node) {
+ ack = client->event_callback(client, chan,
+ DMA_RESOURCE_REMOVED);
+
+ if (ack == DMA_ACK) {
+ dma_chan_put(chan);
+ kref_put(&chan->device->refcount,
+ dma_async_device_cleanup);
+ }
+ }
+
list_del(&client->global_node);
mutex_unlock(&dma_list_mutex);
-
- kfree(client);
- dma_chans_rebalance();
}
EXPORT_SYMBOL(dma_async_client_unregister);
/**
- * dma_async_client_chan_request - request DMA channels
- * @client: &dma_client
- * @number: count of DMA channels requested
- *
- * Clients call dma_async_client_chan_request() to specify how many
- * DMA channels they need, 0 to free all currently allocated.
- * The resulting allocations/frees are indicated to the client via the
- * event callback.
+ * dma_async_client_chan_request - send all available channels to the
+ * client that satisfy the capability mask
+ * @client - requester
*/
-void dma_async_client_chan_request(struct dma_client *client,
- unsigned int number)
+void dma_async_client_chan_request(struct dma_client *client)
{
- client->chans_desired = number;
- dma_chans_rebalance();
+ mutex_lock(&dma_list_mutex);
+ dma_client_chan_alloc(client);
+ mutex_unlock(&dma_list_mutex);
}
EXPORT_SYMBOL(dma_async_client_chan_request);
@@ -386,13 +398,16 @@
}
kref_get(&device->refcount);
+ kref_init(&chan->refcount);
+ chan->slow_ref = 0;
+ INIT_RCU_HEAD(&chan->rcu);
}
mutex_lock(&dma_list_mutex);
list_add_tail(&device->global_node, &dma_device_list);
mutex_unlock(&dma_list_mutex);
- dma_chans_rebalance();
+ dma_clients_notify_available();
return 0;
@@ -428,26 +443,16 @@
void dma_async_device_unregister(struct dma_device *device)
{
struct dma_chan *chan;
- unsigned long flags;
mutex_lock(&dma_list_mutex);
list_del(&device->global_node);
mutex_unlock(&dma_list_mutex);
list_for_each_entry(chan, &device->channels, device_node) {
- if (chan->client) {
- spin_lock_irqsave(&chan->client->lock, flags);
- list_del(&chan->client_node);
- chan->client->chan_count--;
- spin_unlock_irqrestore(&chan->client->lock, flags);
- chan->client->event_callback(chan->client,
- chan,
- DMA_RESOURCE_REMOVED);
- dma_client_chan_free(chan);
- }
+ dma_clients_notify_removed(chan);
class_device_unregister(&chan->class_dev);
+ dma_chan_release(chan);
}
- dma_chans_rebalance();
kref_put(&device->refcount, dma_async_device_cleanup);
wait_for_completion(&device->done);