Re: [PATCH net-next V2 7/8] net: fec: don't transfer ownership until descriptor write is complete

[Sergei Shtylyov]

Hello.

On 2/6/2016 12:52 AM, Troy Kisky wrote:

If you don't own it, you shouldn't write to it.

Signed-off-by: Troy Kisky <troy.ki...@boundarydevices.com>
---
  drivers/net/ethernet/freescale/fec_main.c | 14 +++++++++++++-
  1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c 
b/drivers/net/ethernet/freescale/fec_main.c
index ca2708d..97ca72a 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -390,6 +390,10 @@ fec_enet_txq_submit_frag_skb(struct fec_enet_priv_tx_q 
*txq,

                bdp->cbd_bufaddr = cpu_to_fec32(addr);
                bdp->cbd_datlen = cpu_to_fec16(frag_len);
+               /* Make sure the updates to rest of the descriptor are
+                * performed before transferring ownership.
+                */
+               wmb();
                bdp->cbd_sc = cpu_to_fec16(status);
        }

@@ -499,6 +503,10 @@ static int fec_enet_txq_submit_skb(struct 
fec_enet_priv_tx_q *txq,

        bdp->cbd_datlen = cpu_to_fec16(buflen);
        bdp->cbd_bufaddr = cpu_to_fec32(addr);
+       /* Make sure the updates to rest of the descriptor are performed before
+        * transferring ownership.
+        */
+       wmb();

        /* 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.

[...]

@@ -1484,6 +1491,11 @@ rx_processing_done:
                        ebdp->cbd_prot = 0;
                        ebdp->cbd_bdu = 0;
                }
+               /* Make sure the updates to rest of the descriptor are
+                * performed before transferring ownership.
+                */
+               wmb();
+               bdp->cbd_sc = cpu_to_fec16(status);

   I think you can use "ligter" dma_wmb() in this case.

[...]

MBR, Sergei