Re: [PATCH v4 01/10] net: eth: altera: tse_start_xmit ignores tx_buffer call response

From: Dalon Westergreen <redacted>

The return from tx_buffer call in tse_start_xmit is
inapropriately ignored.  tse_buffer calls should return
0 for success or NETDEV_TX_BUSY.  tse_start_xmit should
return not report a successful transmit when the tse_buffer
call returns an error condition.

In addition to the above, the msgdma and sgdma do not return
the same value on success or failure.  The sgdma_tx_buffer
returned 0 on failure and a positive number of transmitted
packets on success.  Given that it only ever sends 1 packet,
this made no sense.  The msgdma implementation msgdma_tx_buffer
returns 0 on success.

   -> Don't ignore the return from tse_buffer calls
   -> Fix sgdma tse_buffer call to return 0 on success
      and NETDEV_TX_BUSY on failure.

Signed-off-by: Dalon Westergreen <redacted>
Signed-off-by: Joyce Ooi <redacted>
---
v2: no change
v3: queue is stopped before returning NETDEV_TX_BUSY
v4: no change
---
  drivers/net/ethernet/altera/altera_sgdma.c    | 19 ++++++++++++-------
  drivers/net/ethernet/altera/altera_tse_main.c |  4 +++-
  2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/altera/altera_sgdma.c b/drivers/net/ethernet/altera/altera_sgdma.c
index db97170da8c7..fe6276c7e4a3 100644
--- a/drivers/net/ethernet/altera/altera_sgdma.c
+++ b/drivers/net/ethernet/altera/altera_sgdma.c

@@ -4,6 +4,7 @@
   */
  
  #include <linux/list.h>
+#include <linux/netdevice.h>
  #include "altera_utils.h"
  #include "altera_tse.h"
  #include "altera_sgdmahw.h"

@@ -159,10 +160,11 @@ void sgdma_clear_txirq(struct altera_tse_private *priv)
  		    SGDMA_CTRLREG_CLRINT);
  }
  
-/* transmits buffer through SGDMA. Returns number of buffers
- * transmitted, 0 if not possible.
- *
- * tx_lock is held by the caller
+/* transmits buffer through SGDMA.
+ *   original behavior returned the number of transmitted packets (always 1) &
+ *   returned 0 on error.  This differs from the msgdma.  the calling function
+ *   will now actually look at the code, so from now, 0 is good and return
+ *   NETDEV_TX_BUSY when busy.
   */
  int sgdma_tx_buffer(struct altera_tse_private *priv, struct tse_buffer *buffer)
  {

@@ -173,8 +175,11 @@ int sgdma_tx_buffer(struct altera_tse_private *priv, struct tse_buffer *buffer)
  	struct sgdma_descrip __iomem *ndesc = &descbase[1];
  
  	/* wait 'til the tx sgdma is ready for the next transmit request */
-	if (sgdma_txbusy(priv))
-		return 0;
+	if (sgdma_txbusy(priv)) {
+		if (!netif_queue_stopped(priv->dev))
+			netif_stop_queue(priv->dev);
+		return NETDEV_TX_BUSY;
+	}
  
  	sgdma_setup_descrip(cdesc,			/* current descriptor */
  			    ndesc,			/* next descriptor */

@@ -191,7 +196,7 @@ int sgdma_tx_buffer(struct altera_tse_private *priv, struct tse_buffer *buffer)
  	/* enqueue the request to the pending transmit queue */
  	queue_tx(priv, buffer);
  
-	return 1;
+	return 0;
  }
  
  

diff --git a/drivers/net/ethernet/altera/altera_tse_main.c b/drivers/net/ethernet/altera/altera_tse_main.c
index 907125abef2c..ec2b36e05c3f 100644
--- a/drivers/net/ethernet/altera/altera_tse_main.c
+++ b/drivers/net/ethernet/altera/altera_tse_main.c

@@ -595,7 +595,9 @@ static netdev_tx_t tse_start_xmit(struct sk_buff *skb, struct net_device *dev)
  	buffer->dma_addr = dma_addr;
  	buffer->len = nopaged_len;
  
-	priv->dmaops->tx_buffer(priv, buffer);
+	ret = priv->dmaops->tx_buffer(priv, buffer);
+	if (ret)
+		goto out;
  
  	skb_tx_timestamp(skb);