netdev - Re: [PATCH net-next V2 07/16] net: fec: set cbd

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Date:	Fri, 4 Mar 2016 09:08:07 -0700
From:	Troy Kisky <troy.kisky@...ndarydevices.com>
To:	Fugang Duan <fugang.duan@....com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"b38611@...escale.com" <b38611@...escale.com>
Cc:	"fabio.estevam@...escale.com" <fabio.estevam@...escale.com>,
	"l.stach@...gutronix.de" <l.stach@...gutronix.de>,
	"andrew@...n.ch" <andrew@...n.ch>,
	"tremyfr@...il.com" <tremyfr@...il.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"laci@...ndarydevices.com" <laci@...ndarydevices.com>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>,
	"johannes@...solutions.net" <johannes@...solutions.net>,
	"stillcompiling@...il.com" <stillcompiling@...il.com>,
	"sergei.shtylyov@...entembedded.com" 
	<sergei.shtylyov@...entembedded.com>,
	"arnd@...db.de" <arnd@...db.de>
Subject: 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 <troy.kisky@...ndarydevices.com> Sent: Thursday, February 25, 2016 8:37 AM
>> To: 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; stillcompiling@...il.com;
>> sergei.shtylyov@...entembedded.com; arnd@...db.de; Troy Kisky
>> <troy.kisky@...ndarydevices.com>
>> 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 <troy.kisky@...ndarydevices.com>
>> ---
>>  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