dmaengine: track the number of clients using a channel

Haavard's dma-slave interface would like to test for exclusive access to a
channel.  The standard channel refcounting is not sufficient in that it
tracks more than just client references, it is also inaccurate as reference
counts are percpu until the channel is removed.

This change also enables a future fix to deallocate resources when a client
declines to use a capable channel.

Acked-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 99c22b42bada..10de69eb1a3e 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -183,9 +183,10 @@ static void dma_client_chan_alloc(struct dma_client *client)
                                 /* we are done once this client rejects
                                  * an available resource
                                  */
-                                if (ack == DMA_ACK)
+                                if (ack == DMA_ACK) {
                                         dma_chan_get(chan);
-                                else if (ack == DMA_NAK)
+                                        chan->client_count++;
+                                } else if (ack == DMA_NAK)
                                         return;
                         }
                 }
@@ -272,8 +273,10 @@ static void dma_clients_notify_removed(struct dma_chan *chan)
                 /* client was holding resources for this channel so
                  * free it
                  */
-                if (ack == DMA_ACK)
+                if (ack == DMA_ACK) {
                         dma_chan_put(chan);
+                        chan->client_count--;
+                }
         }
 
         mutex_unlock(&dma_list_mutex);
@@ -313,8 +316,10 @@ void dma_async_client_unregister(struct dma_client *client)
                         ack = client->event_callback(client, chan,
                                 DMA_RESOURCE_REMOVED);
 
-                        if (ack == DMA_ACK)
+                        if (ack == DMA_ACK) {
                                 dma_chan_put(chan);
+                                chan->client_count--;
+                        }
                 }
 
         list_del(&client->global_node);
@@ -394,6 +399,7 @@ int dma_async_device_register(struct dma_device *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);
         }