netdev - Re: [PATCH 2/6] ibmveth: Implement ethtool hooks to enable/disable checksum offload

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Date:	Tue, 07 Aug 2007 17:07:12 -0500
From:	Brian King <brking@...ux.vnet.ibm.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	santil@...ux.vnet.ibm.com, rcjenn@...ux.vnet.ibm.com,
	netdev@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: [PATCH 2/6] ibmveth: Implement ethtool hooks to enable/disable
 checksum offload

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@...ux.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.

-Brian

-- 
Brian King
Linux on Power Virtualization
IBM Linux Technology Center
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