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

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Message-ID: <CAHXqBF+=zps_sqe8pETcZ7GR_Sk2_Je_nBT_YqdHCyOkuiU-0A@mail.gmail.com>
Date:	Sat, 11 Feb 2012 00:09:07 +0100
From:	Michał Mirosław <mirqus@...il.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v2 03/10] e1000e: Support RXFCS feature flag.

W dniu 10 lutego 2012 23:57 użytkownik Ben Greear
<greearb@...delatech.com> napisał:
> 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.

That makes sense. The flag FLAG2_DFLT_CRC_STRIPPING should be called
FLAG2_FORCE_CRC_STRIPPING_OFF or something if that's the case.
"Default" doesn't tell if that's a strong preference or just because.

Best Regards,
Michał Mirosław
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