async_tx: fix multiple dependency submission

Shrink struct dma_async_tx_descriptor and introduce
async_tx_channel_switch to properly inject a channel switch interrupt in
the descriptor stream.  This simplifies the locking model as drivers no
longer need to handle dma_async_tx_descriptor.lock.

Acked-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

4 files changed, 170 insertions, 47 deletions

diff --git a/crypto/async_tx/async_tx.c b/crypto/async_tx/async_tx.c
index 2be3bae89930..69756164b61d 100644
--- a/crypto/async_tx/async_tx.c
+++ b/crypto/async_tx/async_tx.c
@@ -89,13 +89,19 @@ dma_wait_for_async_tx(struct dma_async_tx_descriptor *tx)
                 iter = tx;
 
                 /* find the root of the unsubmitted dependency chain */
-                while (iter->cookie == -EBUSY) {
+                do {
                         parent = iter->parent;
-                        if (parent && parent->cookie == -EBUSY)
-                                iter = iter->parent;
-                        else
+                        if (!parent)
                                 break;
-                }
+                        else
+                                iter = parent;
+                } while (parent);
+
+                /* there is a small window for ->parent == NULL and
+                 * ->cookie == -EBUSY
+                 */
+                while (iter->cookie == -EBUSY)
+                        cpu_relax();
 
                 status = dma_sync_wait(iter->chan, iter->cookie);
         } while (status == DMA_IN_PROGRESS || (iter != tx));
@@ -111,24 +117,33 @@ EXPORT_SYMBOL_GPL(dma_wait_for_async_tx);
 void
 async_tx_run_dependencies(struct dma_async_tx_descriptor *tx)
 {
-        struct dma_async_tx_descriptor *dep_tx, *_dep_tx;
-        struct dma_device *dev;
+        struct dma_async_tx_descriptor *next = tx->next;
         struct dma_chan *chan;
 
-        list_for_each_entry_safe(dep_tx, _dep_tx, &tx->depend_list,
-                depend_node) {
-                chan = dep_tx->chan;
-                dev = chan->device;
-                /* we can't depend on ourselves */
-                BUG_ON(chan == tx->chan);
-                list_del(&dep_tx->depend_node);
-                tx->tx_submit(dep_tx);
-
-                /* we need to poke the engine as client code does not
-                 * know about dependency submission events
-                 */
-                dev->device_issue_pending(chan);
+        if (!next)
+                return;
+
+        tx->next = NULL;
+        chan = next->chan;
+
+        /* keep submitting up until a channel switch is detected
+         * in that case we will be called again as a result of
+         * processing the interrupt from async_tx_channel_switch
+         */
+        while (next && next->chan == chan) {
+                struct dma_async_tx_descriptor *_next;
+
+                spin_lock_bh(&next->lock);
+                next->parent = NULL;
+                _next = next->next;
+                next->next = NULL;
+                spin_unlock_bh(&next->lock);
+
+                next->tx_submit(next);
+                next = _next;
         }
+
+        chan->device->device_issue_pending(chan);
 }
 EXPORT_SYMBOL_GPL(async_tx_run_dependencies);
 
@@ -397,6 +412,92 @@ static void __exit async_tx_exit(void)
 }
 #endif
 
+
+/**
+ * async_tx_channel_switch - queue an interrupt descriptor with a dependency
+ *      pre-attached.
+ * @depend_tx: the operation that must finish before the new operation runs
+ * @tx: the new operation
+ */
+static void
+async_tx_channel_switch(struct dma_async_tx_descriptor *depend_tx,
+                        struct dma_async_tx_descriptor *tx)
+{
+        struct dma_chan *chan;
+        struct dma_device *device;
+        struct dma_async_tx_descriptor *intr_tx = (void *) ~0;
+
+        /* first check to see if we can still append to depend_tx */
+        spin_lock_bh(&depend_tx->lock);
+        if (depend_tx->parent && depend_tx->chan == tx->chan) {
+                tx->parent = depend_tx;
+                depend_tx->next = tx;
+                intr_tx = NULL;
+        }
+        spin_unlock_bh(&depend_tx->lock);
+
+        if (!intr_tx)
+                return;
+
+        chan = depend_tx->chan;
+        device = chan->device;
+
+        /* see if we can schedule an interrupt
+         * otherwise poll for completion
+         */
+        if (dma_has_cap(DMA_INTERRUPT, device->cap_mask))
+                intr_tx = device->device_prep_dma_interrupt(chan);
+        else
+                intr_tx = NULL;
+
+        if (intr_tx) {
+                intr_tx->callback = NULL;
+                intr_tx->callback_param = NULL;
+                tx->parent = intr_tx;
+                /* safe to set ->next outside the lock since we know we are
+                 * not submitted yet
+                 */
+                intr_tx->next = tx;
+
+                /* check if we need to append */
+                spin_lock_bh(&depend_tx->lock);
+                if (depend_tx->parent) {
+                        intr_tx->parent = depend_tx;
+                        depend_tx->next = intr_tx;
+                        async_tx_ack(intr_tx);
+                        intr_tx = NULL;
+                }
+                spin_unlock_bh(&depend_tx->lock);
+
+                if (intr_tx) {
+                        intr_tx->parent = NULL;
+                        intr_tx->tx_submit(intr_tx);
+                        async_tx_ack(intr_tx);
+                }
+        } else {
+                if (dma_wait_for_async_tx(depend_tx) == DMA_ERROR)
+                        panic("%s: DMA_ERROR waiting for depend_tx\n",
+                              __func__);
+                tx->tx_submit(tx);
+        }
+}
+
+
+/**
+ * submit_disposition - while holding depend_tx->lock we must avoid submitting
+ *      new operations to prevent a circular locking dependency with
+ *      drivers that already hold a channel lock when calling
+ *      async_tx_run_dependencies.
+ * @ASYNC_TX_SUBMITTED: we were able to append the new operation under the lock
+ * @ASYNC_TX_CHANNEL_SWITCH: when the lock is dropped schedule a channel switch
+ * @ASYNC_TX_DIRECT_SUBMIT: when the lock is dropped submit directly
+ */
+enum submit_disposition {
+        ASYNC_TX_SUBMITTED,
+        ASYNC_TX_CHANNEL_SWITCH,
+        ASYNC_TX_DIRECT_SUBMIT,
+};
+
 void
 async_tx_submit(struct dma_chan *chan, struct dma_async_tx_descriptor *tx,
         enum async_tx_flags flags, struct dma_async_tx_descriptor *depend_tx,
@@ -405,28 +506,54 @@ async_tx_submit(struct dma_chan *chan, struct dma_async_tx_descriptor *tx,
         tx->callback = cb_fn;
         tx->callback_param = cb_param;
 
-        /* set this new tx to run after depend_tx if:
-         * 1/ a dependency exists (depend_tx is !NULL)
-         * 2/ the tx can not be submitted to the current channel
-         */
-        if (depend_tx && depend_tx->chan != chan) {
-                /* if ack is already set then we cannot be sure
+        if (depend_tx) {
+                enum submit_disposition s;
+
+                /* sanity check the dependency chain:
+                 * 1/ if ack is already set then we cannot be sure
                  * we are referring to the correct operation
+                 * 2/ dependencies are 1:1 i.e. two transactions can
+                 * not depend on the same parent
                  */
-                BUG_ON(depend_tx->ack);
+                BUG_ON(depend_tx->ack || depend_tx->next || tx->parent);
 
-                tx->parent = depend_tx;
+                /* the lock prevents async_tx_run_dependencies from missing
+                 * the setting of ->next when ->parent != NULL
+                 */
                 spin_lock_bh(&depend_tx->lock);
-                list_add_tail(&tx->depend_node, &depend_tx->depend_list);
-                if (depend_tx->cookie == 0) {
-                        struct dma_chan *dep_chan = depend_tx->chan;
-                        struct dma_device *dep_dev = dep_chan->device;
-                        dep_dev->device_dependency_added(dep_chan);
+                if (depend_tx->parent) {
+                        /* we have a parent so we can not submit directly
+                         * if we are staying on the same channel: append
+                         * else: channel switch
+                         */
+                        if (depend_tx->chan == chan) {
+                                tx->parent = depend_tx;
+                                depend_tx->next = tx;
+                                s = ASYNC_TX_SUBMITTED;
+                        } else
+                                s = ASYNC_TX_CHANNEL_SWITCH;
+                } else {
+                        /* we do not have a parent so we may be able to submit
+                         * directly if we are staying on the same channel
+                         */
+                        if (depend_tx->chan == chan)
+                                s = ASYNC_TX_DIRECT_SUBMIT;
+                        else
+                                s = ASYNC_TX_CHANNEL_SWITCH;
                 }
                 spin_unlock_bh(&depend_tx->lock);
 
-                /* schedule an interrupt to trigger the channel switch */
-                async_trigger_callback(ASYNC_TX_ACK, depend_tx, NULL, NULL);
+                switch (s) {
+                case ASYNC_TX_SUBMITTED:
+                        break;
+                case ASYNC_TX_CHANNEL_SWITCH:
+                        async_tx_channel_switch(depend_tx, tx);
+                        break;
+                case ASYNC_TX_DIRECT_SUBMIT:
+                        tx->parent = NULL;
+                        tx->tx_submit(tx);
+                        break;
+                }
         } else {
                 tx->parent = NULL;
                 tx->tx_submit(tx);
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 8db0e7f9d3f4..9cb898a76bb3 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -600,8 +600,6 @@ void dma_async_tx_descriptor_init(struct dma_async_tx_descriptor *tx,
 {
         tx->chan = chan;
         spin_lock_init(&tx->lock);
-        INIT_LIST_HEAD(&tx->depend_node);
-        INIT_LIST_HEAD(&tx->depend_list);
 }
 EXPORT_SYMBOL(dma_async_tx_descriptor_init);
 
diff --git a/drivers/dma/iop-adma.c b/drivers/dma/iop-adma.c
index f82b0906d466..21854cd7190f 100644
--- a/drivers/dma/iop-adma.c
+++ b/drivers/dma/iop-adma.c
@@ -63,7 +63,6 @@ iop_adma_run_tx_complete_actions(struct iop_adma_desc_slot *desc,
         struct iop_adma_chan *iop_chan, dma_cookie_t cookie)
 {
         BUG_ON(desc->async_tx.cookie < 0);
-        spin_lock_bh(&desc->async_tx.lock);
         if (desc->async_tx.cookie > 0) {
                 cookie = desc->async_tx.cookie;
                 desc->async_tx.cookie = 0;
@@ -101,7 +100,6 @@ iop_adma_run_tx_complete_actions(struct iop_adma_desc_slot *desc,
 
         /* run dependent operations */
         async_tx_run_dependencies(&desc->async_tx);
-        spin_unlock_bh(&desc->async_tx.lock);
 
         return cookie;
 }
@@ -275,8 +273,11 @@ iop_adma_slot_cleanup(struct iop_adma_chan *iop_chan)
 
 static void iop_adma_tasklet(unsigned long data)
 {
-        struct iop_adma_chan *chan = (struct iop_adma_chan *) data;
-        __iop_adma_slot_cleanup(chan);
+        struct iop_adma_chan *iop_chan = (struct iop_adma_chan *) data;
+
+        spin_lock(&iop_chan->lock);
+        __iop_adma_slot_cleanup(iop_chan);
+        spin_unlock(&iop_chan->lock);
 }
 
 static struct iop_adma_desc_slot *
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 34d440698293..91252a7e4d03 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -221,11 +221,9 @@ typedef void (*dma_async_tx_callback)(void *dma_async_param);
  * @callback: routine to call after this operation is complete
  * @callback_param: general parameter to pass to the callback routine
  * ---async_tx api specific fields---
- * @depend_list: at completion this list of transactions are submitted
- * @depend_node: allow this transaction to be executed after another
- *      transaction has completed, possibly on another channel
+ * @next: at completion submit this descriptor
  * @parent: pointer to the next level up in the dependency chain
- * @lock: protect the dependency list
+ * @lock: protect the parent and next pointers
  */
 struct dma_async_tx_descriptor {
         dma_cookie_t cookie;
@@ -236,8 +234,7 @@ struct dma_async_tx_descriptor {
         dma_cookie_t (*tx_submit)(struct dma_async_tx_descriptor *tx);
         dma_async_tx_callback callback;
         void *callback_param;
-        struct list_head depend_list;
-        struct list_head depend_node;
+        struct dma_async_tx_descriptor *next;
         struct dma_async_tx_descriptor *parent;
         spinlock_t lock;
 };