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Date: Tue, 07 Aug 2007 18:16:34 -0400
From: Jeff Garzik <jeff@garzik.org>
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To: brking@linux.vnet.ibm.com
Subject: Re: [PATCH 2/6] ibmveth: Implement ethtool hooks to enable/disable
	checksum offload
References: <11864293333377-patch-mail.ibm.com>
	<200708061942.l76JgLrU009242@d01av04.pok.ibm.com>
	<46B8E891.80403@garzik.org> <46B8ED10.1060701@linux.vnet.ibm.com>
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Cc: linuxppc-dev@ozlabs.org, rcjenn@linux.vnet.ibm.com,
	santil@linux.vnet.ibm.com, netdev@vger.kernel.org
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Brian King wrote:
> Jeff Garzik wrote:
>> Brian King wrote:
>>> This patch adds the appropriate ethtool hooks to allow for enabling/disabling
>>> of hypervisor assisted checksum offload for TCP.
>>>
>>> Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
>>> ---
>>>
>>>  linux-2.6-bjking1/drivers/net/ibmveth.c |  118 +++++++++++++++++++++++++++++++-
>>>  linux-2.6-bjking1/drivers/net/ibmveth.h |    1 
>>>  2 files changed, 117 insertions(+), 2 deletions(-)
>>>
>>> diff -puN drivers/net/ibmveth.c~ibmveth_csum_offload_ethtool drivers/net/ibmveth.c
>>> --- linux-2.6/drivers/net/ibmveth.c~ibmveth_csum_offload_ethtool	2007-08-01 14:55:14.000000000 -0500
>>> +++ linux-2.6-bjking1/drivers/net/ibmveth.c	2007-08-01 14:55:14.000000000 -0500
>>> @@ -641,12 +641,125 @@ static u32 netdev_get_link(struct net_de
>>>  	return 1;
>>>  }
>>>  
>>> +static void ibmveth_set_rx_csum_flags(struct net_device *dev, u32 data)
>>> +{
>>> +	struct ibmveth_adapter *adapter = dev->priv;
>>> +
>>> +	if (data)
>>> +		adapter->rx_csum = 1;
>>> +	else {
>>> +		adapter->rx_csum = 0;
>>> +		dev->features &= ~NETIF_F_IP_CSUM;
>> why does this RX-related code clear a TX-related flag?
> 
> Its related to how the pSeries firmware works. The firmware provides an interface
> to enable "checksum offload", which means both tx and rx checksum offload from
> the firmware's point of view. The firmware does not support enabling checksum
> offload for only rx. If I disable it for rx I have to disable it for tx as
> well, otherwise the firmware will reject all future tx buffers I throw at it
> that are not checksummed.

ACK once you add a comment describing this :)