netdev - Re: [RFC] r8169 : why SG / TX checksum are default disabled

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Message-Id: <20120718.092346.1263036873056516097.davem@davemloft.net>
Date:	Wed, 18 Jul 2012 09:23:46 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	hayeswang@...ltek.com
Cc:	romieu@...zoreil.com, eric.dumazet@...il.com,
	netdev@...r.kernel.org
Subject: Re: [RFC] r8169 : why SG / TX checksum are default disabled

From: hayeswang <hayeswang@...ltek.com>
Date: Wed, 18 Jul 2012 14:45:55 +0800

> Francois Romieu [mailto:romieu@...zoreil.com] 
> [...]
> 
>> Hayes, should we not add into the kernel driver something similar to
>> the rtl8168_start_xmit::skb_checksum_help stuff in Realtek's 
>> 8168 driver ?
>> There seems to be a bug for (skb->len < 60 && RTL_GIGA_MAC_VER_34.
> 
> For RTL8168E-VL (RTL_GIGA_MAC_VER_34), the hardware wouldn't send the packet
> with the length less than 60 bytes. The hardware should pad this kind of packet
> to 60 bytes, but it wouldn't. Therefore, the software has to pad the packet to
> 60 bytes. However, the hw checksum would be incorrect for the modified packet,
> so the software checksum is necessary.

I wonder how the hardware checksum can be incorrectly calculated if the padding
is done with zeros?

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