[PATCH v2] NTB: Address out of DMA descriptor issue with NTB

[Dave Jiang <dave.jiang@intel.com>]

The transport right now does not handle the case where we run out of DMA
descriptors. We just fail when we do not succeed. Adding code to retry for
a bit attempting to use the DMA engine instead of instantly fail to CPU
copy.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---
 drivers/ntb/ntb_transport.c |   48 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 41 insertions(+), 7 deletions(-)

diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index 60654d5..8da0e6c 100644
--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -171,12 +171,14 @@ struct ntb_transport_qp {
 	u64 rx_err_ver;
 	u64 rx_memcpy;
 	u64 rx_async;
+	u64 dma_rx_prep_err;
 	u64 tx_bytes;
 	u64 tx_pkts;
 	u64 tx_ring_full;
 	u64 tx_err_no_buf;
 	u64 tx_memcpy;
 	u64 tx_async;
+	u64 dma_tx_prep_err;
 };
 
 struct ntb_transport_mw {
@@ -249,6 +251,8 @@ enum {
 #define QP_TO_MW(nt, qp)	((qp) % nt->mw_count)
 #define NTB_QP_DEF_NUM_ENTRIES	100
 #define NTB_LINK_DOWN_TIMEOUT	10
+#define DMA_RETRIES		20
+#define DMA_OUT_RESOURCE_TO	50
 
 static void ntb_transport_rxc_db(unsigned long data);
 static const struct ntb_ctx_ops ntb_transport_ops;
@@ -501,6 +505,12 @@ static ssize_t debugfs_read(struct file *filp, char __user *ubuf, size_t count,
 	out_offset += snprintf(buf + out_offset, out_count - out_offset,
 			       "free tx - \t%u\n",
 			       ntb_transport_tx_free_entry(qp));
+	out_offset += snprintf(buf + out_offset, out_count - out_offset,
+			       "DMA tx prep err - \t%llu\n",
+			       qp->dma_tx_prep_err);
+	out_offset += snprintf(buf + out_offset, out_count - out_offset,
+			       "DMA rx prep err - \t%llu\n",
+			       qp->dma_rx_prep_err);
 
 	out_offset += snprintf(buf + out_offset, out_count - out_offset,
 			       "\n");
@@ -726,6 +736,8 @@ static void ntb_qp_link_down_reset(struct ntb_transport_qp *qp)
 	qp->tx_err_no_buf = 0;
 	qp->tx_memcpy = 0;
 	qp->tx_async = 0;
+	qp->dma_tx_prep_err = 0;
+	qp->dma_rx_prep_err = 0;
 }
 
 static void ntb_qp_link_cleanup(struct ntb_transport_qp *qp)
@@ -1228,6 +1240,7 @@ static void ntb_async_rx(struct ntb_queue_entry *entry, void *offset)
 	struct dmaengine_unmap_data *unmap;
 	dma_cookie_t cookie;
 	void *buf = entry->buf;
+	int retries = 0;
 
 	len = entry->len;
 
@@ -1263,11 +1276,21 @@ static void ntb_async_rx(struct ntb_queue_entry *entry, void *offset)
 
 	unmap->from_cnt = 1;
 
-	txd = device->device_prep_dma_memcpy(chan, unmap->addr[1],
-					     unmap->addr[0], len,
-					     DMA_PREP_INTERRUPT);
-	if (!txd)
+	for (retries = 0; retries < DMA_RETRIES; retries++) {
+		txd = device->device_prep_dma_memcpy(chan, unmap->addr[1],
+						     unmap->addr[0], len,
+						     DMA_PREP_INTERRUPT);
+		if (txd)
+			break;
+
+		set_current_state(TASK_INTERRUPTIBLE);
+		schedule_timeout(DMA_OUT_RESOURCE_TO);
+	}
+
+	if (!txd) {
+		qp->dma_rx_prep_err++;
 		goto err_get_unmap;
+	}
 
 	txd->callback = ntb_rx_copy_callback;
 	txd->callback_param = entry;
@@ -1460,6 +1483,7 @@ static void ntb_async_tx(struct ntb_transport_qp *qp,
 	void __iomem *offset;
 	size_t len = entry->len;
 	void *buf = entry->buf;
+	int retries = 0;
 
 	offset = qp->tx_mw + qp->tx_max_frame * qp->tx_index;
 	hdr = offset + qp->tx_max_frame - sizeof(struct ntb_payload_header);
@@ -1494,10 +1518,20 @@ static void ntb_async_tx(struct ntb_transport_qp *qp,
 
 	unmap->to_cnt = 1;
 
-	txd = device->device_prep_dma_memcpy(chan, dest, unmap->addr[0], len,
-					     DMA_PREP_INTERRUPT);
-	if (!txd)
+	for (retries = 0; retries < DMA_RETRIES; retries++) {
+		txd = device->device_prep_dma_memcpy(chan, dest, unmap->addr[0],
+						     len, DMA_PREP_INTERRUPT);
+		if (txd)
+			break;
+
+		set_current_state(TASK_INTERRUPTIBLE);
+		schedule_timeout(DMA_OUT_RESOURCE_TO);
+	}
+
+	if (!txd) {
+		qp->dma_tx_prep_err++;
 		goto err_get_unmap;
+	}
 
 	txd->callback = ntb_tx_copy_callback;
 	txd->callback_param = entry;