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

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Date:	Wed, 24 Feb 2016 13:39:14 -0700
From:	Troy Kisky <troy.kisky@...ndarydevices.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	netdev@...r.kernel.org, davem@...emloft.net, B38611@...escale.com
Cc:	fabio.estevam@...escale.com, l.stach@...gutronix.de,
	andrew@...n.ch, tremyfr@...il.com, linux@....linux.org.uk,
	linux-arm-kernel@...ts.infradead.org, laci@...ndarydevices.com,
	shawnguo@...nel.org, johannes@...solutions.net, arnd@...db.de
Subject: Re: [PATCH net-next V2 7/8] net: fec: don't transfer ownership until
 descriptor write is complete

On 2/6/2016 4:52 AM, Sergei Shtylyov wrote:
> 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.kisky@...ndarydevices.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.
> 


Thanks for the review, I added a patch to the end of the series to address this.

Troy