[PATCH net v2] net: ftgmac100: Disable hardware checksum on AST2600

[Dylan Hung]

> -----Original Message-----
> From: joel.stan at gmail.com [mailto:joel.stan at gmail.com] On Behalf Of Joel
> Stanley
> Sent: Friday, May 13, 2022 7:20 AM
> To: David S . Miller <davem at davemloft.net>; Jakub Kicinski
> <kuba at kernel.org>; Paolo Abeni <pabeni at redhat.com>; Benjamin
> Herrenschmidt <benh at kernel.crashing.org>; Dylan Hung
> <dylan_hung at aspeedtech.com>; David Wilder <dwilder at us.ibm.com>
> Cc: openbmc at lists.ozlabs.org; netdev at vger.kernel.org;
> linux-kernel at vger.kernel.org; David Wilder <wilder at us.ibm.com>
> Subject: [PATCH net v2] net: ftgmac100: Disable hardware checksum on
> AST2600
> 
> The AST2600 when using the i210 NIC over NC-SI has been observed to
> produce incorrect checksum results with specific MTU values. This was first
> observed when sending data across a long distance set of networks.
> 
> On a local network, the following test was performed using a 1MB file of
> random data.
> 
> On the receiver run this script:
> 
>  #!/bin/bash
>  while [ 1 ]; do
>         # Zero the stats
>         nstat -r  > /dev/null
>         nc -l 9899 > test-file
>         # Check for checksum errors
>         TcpInCsumErrors=$(nstat | grep TcpInCsumErrors)
>         if [ -z "$TcpInCsumErrors" ]; then
>                 echo No TcpInCsumErrors
>         else
>                 echo TcpInCsumErrors = $TcpInCsumErrors
>         fi
>  done
> 
> On an AST2600 system:
> 
>  # nc <IP of  receiver host> 9899 < test-file
> 
> The test was repeated with various MTU values:
> 
>  # ip link set mtu 1410 dev eth0
> 
> The observed results:
> 
>  1500 - good
>  1434 - bad
>  1400 - good
>  1410 - bad
>  1420 - good
> 
> The test was repeated after disabling tx checksumming:
> 
>  # ethtool -K eth0 tx-checksumming off
> 
> And all MTU values tested resulted in transfers without error.
> 
> An issue with the driver cannot be ruled out, however there has been no bug
> discovered so far.
> 
> David has done the work to take the original bug report of slow data transfer
> between long distance connections and triaged it down to this test case.
> 
> The vendor suspects this this is a hardware issue when using NC-SI. The fixes
> line refers to the patch that introduced AST2600 support.
> 
> Fixes: 39bfab8844a0 ("net: ftgmac100: Add support for DT phy-handle
> property")
> Reported-by: David Wilder <wilder at us.ibm.com>
> Signed-off-by: Joel Stanley <joel at jms.id.au>
> ---
> v2 updates the commit message with confirmation form the vendor that this is
> a hardware issue, and clarifes why the commit used in the fixes tag was
> chosen.
> 
>  drivers/net/ethernet/faraday/ftgmac100.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/ethernet/faraday/ftgmac100.c
> b/drivers/net/ethernet/faraday/ftgmac100.c
> index caf48023f8ea..5231818943c6 100644
> --- a/drivers/net/ethernet/faraday/ftgmac100.c
> +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> @@ -1928,6 +1928,11 @@ static int ftgmac100_probe(struct platform_device
> *pdev)
>  	/* AST2400  doesn't have working HW checksum generation */
>  	if (np && (of_device_is_compatible(np, "aspeed,ast2400-mac")))
>  		netdev->hw_features &= ~NETIF_F_HW_CSUM;
> +
> +	/* AST2600 tx checksum with NC-SI is broken */
> +	if (priv->use_ncsi && of_device_is_compatible(np,
> "aspeed,ast2600-mac"))
> +		netdev->hw_features &= ~NETIF_F_HW_CSUM;
> +
>  	if (np && of_get_property(np, "no-hw-checksum", NULL))
>  		netdev->hw_features &= ~(NETIF_F_HW_CSUM |
> NETIF_F_RXCSUM);
>  	netdev->features |= netdev->hw_features;
> --
> 2.35.1
Reviewed-by: Dylan Hung <dylan_hung at aspeedtech.com>