netdev - RE: [net] e1000: Small packets may get corrupted during padding by HW

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Date:	Sun, 16 Sep 2012 01:25:45 +0000
From:	"Dave, Tushar N" <tushar.n.dave@...el.com>
To:	Michal Miroslaw <mirqus@...il.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>
Subject: RE: [net] e1000: Small packets may get corrupted during padding by
 HW

>-----Original Message-----
>From: Michał Mirosław [mailto:mirqus@...il.com]
>Sent: Saturday, September 15, 2012 1:45 PM
>To: Kirsher, Jeffrey T
>Cc: davem@...emloft.net; Dave, Tushar N; netdev@...r.kernel.org;
>gospo@...hat.com; sassmann@...hat.com
>Subject: Re: [net] e1000: Small packets may get corrupted during padding
>by HW
>
>2012/9/15 Jeff Kirsher <jeffrey.t.kirsher@...el.com>:
>> From: Tushar Dave <tushar.n.dave@...el.com>
>>
>> On PCI/PCI-X HW, if packet size is less than ETH_ZLEN, packets may get
>> corrupted during padding by HW.
>> To WA this issue, pad all small packets manually.
>>
>> Signed-off-by: Tushar Dave <tushar.n.dave@...el.com>
>> Tested-by: Aaron Brown <aaron.f.brown@...el.com>
>> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
>> ---
>>  drivers/net/ethernet/intel/e1000/e1000_main.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c
>> b/drivers/net/ethernet/intel/e1000/e1000_main.c
>> index 3bfbb8d..bde337e 100644
>> --- a/drivers/net/ethernet/intel/e1000/e1000_main.c
>> +++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
>> @@ -3149,6 +3149,17 @@ static netdev_tx_t e1000_xmit_frame(struct
>sk_buff *skb,
>>                 return NETDEV_TX_OK;
>>         }
>>
>> +       /* On PCI/PCI-X HW, if packet size is less than ETH_ZLEN,
>> +        * packets may get corrupted during padding by HW.
>> +        * To WA this issue, pad all small packets manually.
>> +        */
>> +       if (skb->len < ETH_ZLEN) {
>> +               if (skb_pad(skb, ETH_ZLEN - skb->len))
>> +                       return NETDEV_TX_OK;
>> +               skb->len = ETH_ZLEN;
>> +               skb_set_tail_pointer(skb, ETH_ZLEN);
>> +       }
>> +
>
>Isn't there a skb_padto() that does just this?

Skb_padto calls skb_pad(). Calling skb_pad directly saves some cycles.

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