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 13:38:32 -0700
From:	Troy Kisky <troy.kisky@...ndarydevices.com>
To:	Joshua Clayton <stillcompiling@...il.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, B38611@...escale.com,
	fabio.estevam@...escale.com, andrew@...n.ch,
	linux@....linux.org.uk, arnd@...db.de, laci@...ndarydevices.com,
	johannes@...solutions.net, l.stach@...gutronix.de,
	shawnguo@...nel.org, linux-arm-kernel@...ts.infradead.org,
	tremyfr@...il.com
Subject: Re: [PATCH net-next V2 7/8] net: fec: don't transfer ownership until
 descriptor write is complete

On 2/5/2016 6:03 PM, Joshua Clayton wrote:
> On Fri,  5 Feb 2016 14:52:49 -0700
> Troy Kisky <troy.kisky@...ndarydevices.com> 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);
> You use almost exactly the same code in each place.
> I'd prefer to have wmb(); bdp->cbd_sc = cpu_to_fec16(status) wrapped in
> a function or function like macro, and put the comment in one place.
> 

Thanks for the review. I added a patch to the end of the series to create a common
"trigger_tx" subroutine which should address this.