Re: [PATCH net-next V2 07/16] net: fec: set cbd_sc without relying on previous value

On 3/4/2016 2:29 AM, Fugang Duan wrote:

From: Troy Kisky <redacted> Sent: Thursday, February 25, 2016 8:37 AM

quoted

To: netdev@vger.kernel.org; davem@davemloft.net; b38611@freescale.com
Cc: fabio.estevam@freescale.com; l.stach@pengutronix.de; andrew@lunn.ch;
tremyfr@gmail.com; linux@arm.linux.org.uk; linux-arm-
kernel@lists.infradead.org; laci@boundarydevices.com; shawnguo@kernel.org;
johannes@sipsolutions.net; stillcompiling@gmail.com;
sergei.shtylyov@cogentembedded.com; arnd@arndb.de; Troy Kisky
[off-list ref]
Subject: [PATCH net-next V2 07/16] net: fec: set cbd_sc without relying on
previous value

Relying on the wrap bit to stay valid once initialized when the controller also
writes to this byte seems undesirable since we can easily know what the value
should be.

Signed-off-by: Troy Kisky <redacted>
---
 drivers/net/ethernet/freescale/fec_main.c | 38 +++++++++----------------------
 1 file changed, 11 insertions(+), 27 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c

b/drivers/net/ethernet/freescale/fec_main.c
index 791f385..6ceb5f9 100644

--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c

@@ -340,9 +340,8 @@ fec_enet_txq_submit_frag_skb(struct

fec_enet_priv_tx_q *txq,
 		bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
 		ebdp = (struct bufdesc_ex *)bdp;

-		status = fec16_to_cpu(bdp->cbd_sc);
-		status &= ~BD_ENET_TX_STATS;
-		status |= (BD_ENET_TX_TC | BD_ENET_TX_READY);
+		status = BD_ENET_TX_TC | BD_ENET_TX_READY |
+				((bdp == txq->bd.last) ? BD_SC_WRAP : 0);
 		frag_len = skb_shinfo(skb)->frags[frag].size;

 		/* Handle the last BD specially */

@@ -436,8 +435,6 @@ static int fec_enet_txq_submit_skb(struct

fec_enet_priv_tx_q *txq,
 	/* Fill in a Tx ring entry */
 	bdp = txq->bd.cur;
 	last_bdp = bdp;
-	status = fec16_to_cpu(bdp->cbd_sc);
-	status &= ~BD_ENET_TX_STATS;

 	/* Set buffer length and buffer pointer */
 	bufaddr = skb->data;

@@ -462,6 +459,8 @@ static int fec_enet_txq_submit_skb(struct

fec_enet_priv_tx_q *txq,
 		return NETDEV_TX_OK;
 	}

+	status = BD_ENET_TX_TC | BD_ENET_TX_READY |
+			((bdp == txq->bd.last) ? BD_SC_WRAP : 0);
 	if (nr_frags) {
 		last_bdp = fec_enet_txq_submit_frag_skb(txq, skb, ndev);
 		if (IS_ERR(last_bdp)) {

@@ -512,7 +511,6 @@ static int fec_enet_txq_submit_skb(struct

fec_enet_priv_tx_q *txq,
 	/* Send it on its way.  Tell FEC it's ready, interrupt when done,
 	 * it's the last BD of the frame, and to put the CRC on the end.
 	 */
-	status |= (BD_ENET_TX_READY | BD_ENET_TX_TC);

This is completely error.  We have to prepare all BDs for frag skb, and then enable "READY" and "TC" bit for the first BD, otherwise uDMA copy un-correct data to fifo.

I don't follow. Please read patch again.


Thanks
Troy