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Subject: Re: [PATCH 2/3] net:ethernet:rmnet:Support for downlink MAPv5 csum
 offload
To:     Jakub Kicinski <kuba@kernel.org>
Cc:     Sharath Chandra Vurukala <sharathv@codeaurora.org>,
        davem@davemloft.net, elder@kernel.org, cpratapa@codeaurora.org,
        subashab@codeaurora.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
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From:   Alex Elder <elder@ieee.org>
Message-ID: <dfa87271-0ade-f8b5-b41f-1128353b3248@ieee.org>
Date:   Fri, 12 Feb 2021 13:06:56 -0600
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On 2/12/21 12:51 PM, Jakub Kicinski wrote:
> On Fri, 12 Feb 2021 08:01:15 -0600 Alex Elder wrote:
>> On 2/11/21 8:04 PM, Jakub Kicinski wrote:
>>> On Fri, 12 Feb 2021 03:05:23 +0530 Sharath Chandra Vurukala wrote:
>>>> +/* MAP CSUM headers */
>>>> +struct rmnet_map_v5_csum_header {
>>>> +	u8  next_hdr:1;
>>>> +	u8  header_type:7;
>>>> +	u8  hw_reserved:5;
>>>> +	u8  priority:1;
>>>> +	u8  hw_reserved_bit:1;
>>>> +	u8  csum_valid_required:1;
>>>> +	__be16 reserved;
>>>> +} __aligned(1);
>>>
>>> Will this work on big endian?
>>
>> Sort of related to this point...
>>
>> I'm sure the response to this will be to add two versions
>> of the definition, surrounded __LITTLE_ENDIAN_BITFIELD
>> and __BIG_ENDIAN_BITFIELD tests.
>>
>> I really find this non-intuitive, and every time I
>> look at it I have to think about it a bit to figure
>> out where the bits actually lie in the word.
>>
>> I know this pattern is used elsewhere in the networking
>> code, but that doesn't make it any easier for me to
>> understand...
>>
>> Can we used mask, defined in host byte order, to
>> specify the positions of these fields?
>>
>> I proposed a change at one time that did this and
>> this *_ENDIAN_BITFIELD thing was used instead.
>>
>> I will gladly implement this change (completely
>> separate from what's being done here), but thought
>> it might be best to see what people think about it
>> before doing that work.
> 
> Most definitely agree, please convert.

KS, would you like me to do this to the existing code
first?

I don't think it will take me very long.  If it were
a priority I could probably get it done by the end of
today, but I'd want to ensure the result worked for
the testing you do.

					-Alex