RE: [PATCH 05/14] net: axienet: Factor out TX descriptor chain cleanup

-----Original Message-----
From: Andre Przywara <andre.przywara@arm.com>
Sent: Friday, January 10, 2020 5:24 PM
To: David S . Miller <davem@davemloft.net>; Radhey Shyam Pandey
[off-list ref]
Cc: Michal Simek <redacted>; Robert Hancock
[off-list ref]; netdev@vger.kernel.org; linux-arm-
kernel@lists.infradead.org; linux-kernel@vger.kernel.org
Subject: [PATCH 05/14] net: axienet: Factor out TX descriptor chain cleanup

Factor out the code that cleans up a number of connected TX descriptors,
as we will need it to properly roll back a failed _xmit() call.
There are subtle differences between cleaning up a successfully sent
chain (unknown number of involved descriptors, total data size needed)
and a chain that was about to set up (number of descriptors known), so
cater for those variations with some extra parameters.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 .../net/ethernet/xilinx/xilinx_axienet_main.c | 75 ++++++++++++-------
 1 file changed, 50 insertions(+), 25 deletions(-)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c

b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index ec5d01adc1d5..82abe2b0f16a 100644

--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c

@@ -543,33 +543,37 @@ static int axienet_device_reset(struct net_device

*ndev)
 	return 0;
 }

-/**
- * axienet_start_xmit_done - Invoked once a transmit is completed by the
- * Axi DMA Tx channel.
- * @ndev:	Pointer to the net_device structure
- *
- * This function is invoked from the Axi DMA Tx isr to notify the completion
- * of transmit operation. It clears fields in the corresponding Tx BDs and
- * unmaps the corresponding buffer so that CPU can regain ownership of
the
- * buffer. It finally invokes "netif_wake_queue" to restart transmission if
- * required.
+/* Clean up a series of linked TX descriptors. Would either be called
+ * after a successful transmit operation, or after there was an error
+ * when setting up the chain.
+ * Returns the number of descriptors handled.
  */
-static void axienet_start_xmit_done(struct net_device *ndev)

+static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
+				 int nr_bds, u32 *sizep)
 {
-	u32 size = 0;
-	u32 packets = 0;
 	struct axienet_local *lp = netdev_priv(ndev);
+	int max_bds = (nr_bds != -1) ? nr_bds : lp->tx_bd_num;
 	struct axidma_bd *cur_p;
-	unsigned int status = 0;
+	unsigned int status;
+	int i;
+
+	for (i = 0; i < max_bds; i++) {
+		cur_p = &lp->tx_bd_v[(first_bd + i) % lp->tx_bd_num];
+		status = cur_p->status;
+
+		/* If no number is given, clean up *all* descriptors that have
+		 * been completed by the MAC.
+		 */
+		if (nr_bds == -1 && !(status &
XAXIDMA_BD_STS_COMPLETE_MASK))
+			break;

-	cur_p = &lp->tx_bd_v[lp->tx_bd_ci];
-	status = cur_p->status;
-	while (status & XAXIDMA_BD_STS_COMPLETE_MASK) {
 		dma_unmap_single(ndev->dev.parent, cur_p->phys,
 				(cur_p->cntrl &
XAXIDMA_BD_CTRL_LENGTH_MASK),
 				DMA_TO_DEVICE);
-		if (cur_p->skb)
+
+		if (cur_p->skb && (status &
XAXIDMA_BD_STS_COMPLETE_MASK))
 			dev_consume_skb_irq(cur_p->skb);
+
 		cur_p->cntrl = 0;
 		cur_p->app0 = 0;
 		cur_p->app1 = 0;

@@ -578,15 +582,36 @@ static void axienet_start_xmit_done(struct

net_device *ndev)
 		cur_p->status = 0;
 		cur_p->skb = NULL;

-		size += status & XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
-		packets++;
-
-		if (++lp->tx_bd_ci >= lp->tx_bd_num)
-			lp->tx_bd_ci = 0;
-		cur_p = &lp->tx_bd_v[lp->tx_bd_ci];
-		status = cur_p->status;
+		if (sizep)
+			*sizep += status &
XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
 	}

+	return i;
+}
+
+/**
+ * axienet_start_xmit_done - Invoked once a transmit is completed by the
+ * Axi DMA Tx channel.
+ * @ndev:	Pointer to the net_device structure
+ *
+ * This function is invoked from the Axi DMA Tx isr to notify the completion
+ * of transmit operation. It clears fields in the corresponding Tx BDs and
+ * unmaps the corresponding buffer so that CPU can regain ownership of
the
+ * buffer. It finally invokes "netif_wake_queue" to restart transmission if
+ * required.
+ */
+static void axienet_start_xmit_done(struct net_device *ndev)
+{
+	u32 size = 0;
+	u32 packets = 0;
+	struct axienet_local *lp = netdev_priv(ndev);
+
+	packets = axienet_free_tx_chain(ndev, lp->tx_bd_ci, -1, &size);
+
+	lp->tx_bd_ci += packets;
+	if (lp->tx_bd_ci >= lp->tx_bd_num)
+		lp->tx_bd_ci -= lp->tx_bd_num;
+
 	ndev->stats.tx_packets += packets;
 	ndev->stats.tx_bytes += size;

--
2.17.1