netdev - Re: [net-next 07/11] e1000e: cleanup Rx checksum offload code

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Date:	Tue, 03 Jan 2012 17:02:13 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	bhutchings@...arflare.com
Cc:	jeffrey.t.kirsher@...el.com, bruce.w.allan@...el.com,
	netdev@...r.kernel.org, gospo@...hat.com, sassmann@...hat.com
Subject: Re: [net-next 07/11] e1000e: cleanup Rx checksum offload code

From: Ben Hutchings <bhutchings@...arflare.com>
Date: Tue, 3 Jan 2012 21:24:02 +0000

> On Tue, 2012-01-03 at 16:15 -0500, David Miller wrote:
>> From: Ben Hutchings <bhutchings@...arflare.com>
>> Date: Tue, 3 Jan 2012 21:00:12 +0000
>> 
>> > On Tue, 2012-01-03 at 15:08 -0500, David Miller wrote:
>> >> From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
>> >> Date: Tue,  3 Jan 2012 11:19:12 -0800
>> >> 
>> >> > -		__sum16 sum = (__force __sum16)htons(csum);
>> >> > +		__sum16 sum = (__force __sum16)htons(le16_to_cpu(csum));
>> >> 
>> >> Looks like a NOP.  It's essentially "cpu_to_le16(le16_to_cpu(csum)" as
>> >> far as I can tell.
>> > 
>> > Looks like a swab() to me...
>> 
>> I don't see how it can be.  It's effectively doing a 16-bit swap and
>> then a 16-bit swap again, which is a NOP.
>> 
>> It's the same as "(__force __sum16) csum" and I bet if the code above
>> works, then this expression I'm suggesting will work too.
> 
> In this part of the universe, network order is big-endian.

Indeed, you're right, therefore this is something like swab().
:-)
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