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

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Message-ID: <4F35B111.4010904@candelatech.com>
Date:	Fri, 10 Feb 2012 16:06:41 -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 03:09 PM, Michał Mirosław wrote:
> 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.

The new flag is just to store the original crc-stripping preference
configured by the module options.  It's not really forcing anything,
it is just the 'default' value.

So, I don't think it should be changed.  However, I will defer to the
driver maintainers...if they think I should change it, then I will,
otherwise, I'm going to leave it as is.

Thanks,
Ben

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

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