net_dma: acquire/release dma channels on ifup/ifdown

The recent dmaengine rework removed the capability to remove dma device
driver modules while net_dma is active.  Rather than notify
dmaengine-clients that channels are trying to be removed, we now rely on
clients to notify dmaengine when they no longer have a need for
channels.  Teach net_dma to release channels by taking dmaengine
references at netdevice open and dropping references at netdevice close.

Acked-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 20 insertions, 3 deletions

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 64dea2ab326c..c73f1e2b59b7 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -270,8 +270,18 @@ struct dma_device {
 
 /* --- public DMA engine API --- */
 
+#ifdef CONFIG_DMA_ENGINE
 void dmaengine_get(void);
 void dmaengine_put(void);
+#else
+static inline void dmaengine_get(void)
+{
+}
+static inline void dmaengine_put(void)
+{
+}
+#endif
+
 dma_cookie_t dma_async_memcpy_buf_to_buf(struct dma_chan *chan,
         void *dest, void *src, size_t len);
 dma_cookie_t dma_async_memcpy_buf_to_pg(struct dma_chan *chan,
diff --git a/net/core/dev.c b/net/core/dev.c
index 5f736f1ceeae..b715a55cccc4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1088,6 +1088,11 @@ int dev_open(struct net_device *dev)
                 dev->flags |= IFF_UP;
 
                 /*
+                 *      Enable NET_DMA
+                 */
+                dmaengine_get();
+
+                /*
                  *      Initialize multicasting status
                  */
                 dev_set_rx_mode(dev);
@@ -1164,6 +1169,11 @@ int dev_close(struct net_device *dev)
          */
         call_netdevice_notifiers(NETDEV_DOWN, dev);
 
+        /*
+         *      Shutdown NET_DMA
+         */
+        dmaengine_put();
+
         return 0;
 }
 
@@ -5151,9 +5161,6 @@ static int __init net_dev_init(void)
         hotcpu_notifier(dev_cpu_callback, 0);
         dst_init();
         dev_mcast_init();
-        #ifdef CONFIG_NET_DMA
-        dmaengine_get();
-        #endif
         rc = 0;
 out:
         return rc;