netdev - Re: [PATCH v2 03/10] e1000e: Support RXFCS feature flag.

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Date:	Fri, 10 Feb 2012 14:57:49 -0800
From:	Ben Greear <greearb@...delatech.com>
To:	Michał Mirosław <mirqus@...il.com>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH v2 03/10] e1000e: Support RXFCS feature flag.

On 02/10/2012 02:46 PM, Michał Mirosław wrote:
> 2012/2/8<greearb@...delatech.com>:
>> From: Ben Greear<greearb@...delatech.com>
>>
>> This enables enabling/disabling reception of the Ethernet
>> FCS.  This can be useful when sniffing packets.
>>
>> For e1000e, enabling RXFCS can change the default
>> behaviour for how the NIC handles CRC.  Disabling RXFCS
>> will take the NIC back to defaults, which can be configured
>> as part of the module options.
> [...]
>
> This is not how I would expect the features to behave. Default value
> should be set on probe() time, and when you disable RXFCS it should
> just get disabled.

The NIC itself may still receive the FCS, but it will be removed
before the pkt is sent up the stack once you disable the 'rx-fcs' flag.

My goal was to make sure that if you enabled and then disabled the
new rx-fcs flag, then you would be back at the original behaviour.

I think that if the "rx-fcs off" logic is to change the default
behaviour, then the Intel folks probably need to make those changes:
It seems that there are some tricky work-arounds regarding fcs and
segmented packets for at least some versions of the e1000e chipsets.

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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